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Java Programming Course

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Chapter 1 of 13

Creating Java Programs

1.1 Learning Programming Terminology

Before we dive into writing code, it's crucial to understand some key terms that form the language of programming.

Source Code: The programming statements you write in a high-level language like Java are known as source code. You will write your source code using a plain text editor or a development environment like Eclipse or NetBeans.

Java Virtual Machine (JVM): Java programs don't execute instructions directly on a computer's hardware. Instead, they run on a hypothetical computer called the Java Virtual Machine (JVM), which is a software entity. This feature makes Java "architecturally neutral," allowing a single program to run on any operating system (e.g., Windows, macOS, Linux) or device. The slogan "write once, run anywhere" (WORA) was developed by Sun Microsystems to describe this ability. The JVM also enhances security by isolating the Java program from your computer's operating system.

Bytecode: After you write your Java source code, a Java compiler converts it into a binary program called bytecode. This bytecode is then checked by a Java interpreter, which communicates with the operating system to execute the instructions line by line within the JVM.

Syntax Errors: These are programming errors that violate the rules of the language. A program with syntax errors cannot be compiled.

Logic Errors: These occur when a program's statements are grammatically correct but produce unexpected or incorrect results.

Objects: Objects are central to object-oriented programming. They are created instances of a class. A well-written program allows a user to interact with an object's methods without needing to know the low-level details of how those methods are executed.

Methods: Methods are a feature of a class.

Polymorphism: This term literally means "many forms" and describes the feature of a language that allows the same word or symbol to be interpreted correctly in different situations based on context. For example, the + symbol performs addition with numbers but can also be used to concatenate strings.

1.2 Comparing Procedural and Object-Oriented Programming

Programming paradigms are different ways of organizing and structuring code. Two of the most common are procedural and object-oriented programming.

Procedural Programming: In this approach, a program is a series of steps or procedures that accomplish a task. It focuses on the process a program follows to complete a task. You can think of it as a recipe—a step-by-step list of instructions.

Object-Oriented Programming (OOP): OOP is a way of thinking about programs as collections of interacting objects. It focuses on the objects and their attributes (data) and methods (actions). This approach models the real world, where objects possess both characteristics and abilities.

Encapsulation: In OOP, encapsulation is the principle of containing an object's data and methods within a single unit. It protects data by "hiding" it within an object.

Inheritance: A key feature of OOP, inheritance is the ability to create classes that share the attributes and methods of existing classes, but with more specialized features. For example, a Convertible class can inherit from an Automobile class, gaining all its traits while adding its own unique characteristics.

1.3 Creating and Running Your First Java Program

Now let's get hands-on and write our first Java application. We will create a program that produces console output.

Step 1: Write the Source Code

Every Java program must contain a class with a name, and that name must match the name of the file you save it as. It is a convention to use a public class, and if a class is public, it must be saved in a file with the same name and a .java extension.

Let's look at a simple Hello class:

public class Hello {
  public static void main(String[] args) {
    System.out.println("Hello, world!");
  }
}

• public class Hello: This line declares a class named Hello.
• public static void main(String[] args): This is the main() method header. Every Java application that can be run from the command line must have a main() method. It's the starting point of the program.
• System.out.println("Hello, world!");: This statement prints the phrase "Hello, world!" to the console and moves the cursor to the next line. The System.out object represents the standard output device, which is usually the monitor.

Step 2: Save the File

Save the code in a file named Hello.java. Remember, the file name must exactly match the public class name.

Step 3: Compile the Class

To compile the class from the command line, you will use the javac command followed by the filename.

javac Hello.java

This command invokes the Java compiler. If there are no syntax errors, a file named Hello.class (containing the bytecode) will be created.

Correcting Syntax Errors: If the compiler finds a syntax error, it will provide an error message. A single syntax error can sometimes lead to multiple error messages. You must fix all syntax errors before the program can be compiled successfully.

Step 4: Run the Application

To run the compiled program, use the java command followed by the class name (without the .class extension).

java Hello

The Java interpreter (JVM) will execute the bytecode, and you will see "Hello, world!" printed on the console.

Correcting Logic Errors: If the program runs but produces incorrect output, you have a logic error. These errors are not caught by the compiler and must be fixed by the programmer.

1.4 Adding Comments to Your Code

Comments are non-executing statements that you add to a program for documentation. They are for people reading the source code, not for the computer. Using comments is a best practice, as they help you and others remember why you wrote certain lines of code.

• Line Comments: Start with two forward slashes (//) and continue to the end of the line. They do not require an ending symbol.
• Block Comments: Start with a forward slash and an asterisk (/*) and end with an asterisk and a forward slash (*/). They can extend across multiple lines.
• Javadoc Comments: A special type of block comment that begins with a forward slash and two asterisks (/**) and ends with an asterisk and a forward slash (*/). They are used to automatically generate documentation.

1.5 Important Considerations

"Don't Do It": It's easy to make mistakes when starting out. Avoid common pitfalls like using the assignment operator (=) instead of the equivalency operator (==) when comparing values in decision-making statements. Always remember to use the correct operator for the task at hand.

Getting Help: Programmers must know how to find information on their own. The Java website is a great resource for investigating classes and methods. This course encourages you to be an independent researcher, as computer languages are constantly evolving.

Chapter 1 Summary

• Java is an object-oriented, architecturally neutral language that runs on the Java Virtual Machine (JVM).
• Source code is compiled into bytecode before being executed by the Java interpreter.
• Classes are blueprints for objects, which are instances of a class.
• Programming errors can be either syntax errors (prevent compilation) or logic errors (produce incorrect results).
• Comments are crucial for documenting your code and come in three types: line, block, and Javadoc.

Chapter Notes

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Chapter 2 of 13

Using Data Within a Program

2.1 Declaring Variables

A variable is a named memory location that stores a value. Before you can use a variable, you must declare it. This process involves giving the variable a name and specifying its data type.

Syntax: dataType variableName;

Example: int myNumber;

A variable declaration tells the compiler three things:

• The variable's name (e.g., myNumber).
• The data type of the information it can hold (e.g., int for integer).
• The amount of memory to reserve for the variable.

A primitive data type is a simple, fundamental data type built into the language, such as int, char, or double.

You can also initialize a variable with a value at the time of its declaration.

Syntax: dataType variableName = value;

Example: int myNumber = 500;

The assignment operator (=) is used to assign a value to a variable.

2.2 Understanding Data Types

Java has several primitive data types to store different kinds of values:

• byte: Stores a small integer (8 bits, -128 to 127).
• short: Stores a short integer (16 bits).
• int: Stores a standard integer (32 bits).
• long: Stores a large integer (64 bits). Use this for very large numbers like a population count.
• float: Stores a single-precision floating-point number (32 bits, for values with decimal places).
• double: Stores a double-precision floating-point number (64 bits, the default for decimal numbers in Java).
• char: Stores a single character (16 bits, using Unicode).
• boolean: Stores a true or false value.

A literal constant is a value that is taken literally, such as the number 15 or the character 'A'.

A Note on Unicode: Java uses Unicode, a 16-bit encoding scheme, to represent characters. This allows it to handle characters from a wide range of languages.

2.3 Using Arithmetic Operators

Arithmetic operators are used to perform mathematical calculations.

Operator	Action	Example
+	Addition	3 + 5
-	Subtraction	8 - 2
*	Multiplication	4 * 6
/	Division	10 / 2
%	Remainder	10 % 3

The order of precedence for arithmetic operations is similar to algebra:

• Multiplication, Division, Remainder (*, /, %)
• Addition, Subtraction (+, -)

Expressions inside parentheses are evaluated first.

You can also use combined assignment operators for more concise code:

• x += 5; is equivalent to x = x + 5;
• x -= 5; is equivalent to x = x - 5;

2.4 Working with Input and Output

To create interactive programs, you need to be able to accept input from the user. The Scanner class is an excellent tool for this.

Using the Scanner Class:

• Import: Add import java.util.Scanner; at the top of your program.
• Create an Object: Scanner input = new Scanner(System.in);
• Read Input: Use methods like input.nextInt(), input.nextDouble(), or input.nextLine() to read different data types.

Example Program with Scanner:

import java.util.Scanner;

public class BasicInput {
  // Create a Scanner object to read user input
    Scanner input = new Scanner(System.in);

    System.out.print("Enter your name: ");
    String name = input.nextLine();

    System.out.print("Enter your age: ");
    int age = input.nextInt();

    System.out.println("Hello, " + name + "! You are " + age + " years old.");
  }
}

System.out.print() vs. System.out.println(): The print() method displays output without moving the cursor to the next line, allowing subsequent output to appear on the same line.

2.5 Understanding Scope

The scope of a variable refers to the part of a program where it is accessible. In Java, a variable's scope is defined by the code block in which it is declared, typically indicated by a pair of curly braces {}.

• A variable declared within a method is a local variable. It is only accessible within that method.
• Once a variable goes out of scope (e.g., the method finishes executing), it is no longer available.

2.6 Working with Constants

A constant is an identifier whose value cannot be changed during the program's execution. It is declared using the final keyword.

Syntax: final dataType CONSTANT_NAME = value;

Example: final double PI = 3.14159;

It's a convention to name constants using all uppercase letters to distinguish them from variables. Constants are useful for storing values that should not change, such as mathematical constants or tax rates.

Chapter 2 Summary

• Variables are named memory locations used to store data, and they must be declared with a data type.
• Java has eight primitive data types: byte, short, int, long, float, double, char, and boolean.
• Arithmetic operators (+, -, *, /, %) are used for calculations, and their order of precedence is crucial.
• The Scanner class, part of the java.util package, is used to get user input.
• The scope of a variable determines where in the program it can be used.
• Constants, declared with the final keyword, are values that do not change during program execution.

Chapter Notes

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Chapter 3 of 13

Making Decisions

Welcome back to your Java Programming Course! We've covered the basics of creating programs and using data. Now, in Chapter 3, we'll learn about making decisions in our code, which is a core concept in programming.

3.1 Understanding Boolean Expressions

A Boolean expression is an expression that evaluates to either true or false. These expressions are the foundation of decision-making in programming. You will use them within control structures like if statements to control the flow of your program.

3.2 Using the if Statement

The if statement is the most basic control structure for making decisions. It allows a statement or a block of statements to be executed only if a specific condition is met.

Syntax:

if (BooleanExpression)
{
   // statements to execute if the expression is true
}

Example:

int score = 90;
if (score >= 60)
{
   System.out.println("You passed the exam.");
}

In this example, the message "You passed the exam." will only be printed if the score is greater than or equal to 60.

3.3 Comparison Operators

Comparison operators are used within Boolean expressions to compare two values.

Operator	Meaning
==	Equal to
!=	Not equal to
>	Greater than
<	Less than
>=	Greater than or equal to
<=	Less than or equal to

A very important note: Do not confuse the equality operator (==) with the assignment operator (=). Using = in an if statement will cause a syntax error, as it attempts to assign a value instead of comparing.

3.4 Using the if-else Statement

The if-else statement provides an alternative path to execute when the condition in the if statement is false.

Syntax:

if (BooleanExpression)
{
   // statements for the true case
}
else
{
   // statements for the false case
}

Example:

int age = 17;
if (age >= 18)
{
   System.out.println("You are eligible to vote.");
}
else
{
   System.out.println("You are not yet eligible to vote.");
}

This program will print "You are not yet eligible to vote." because the condition age >= 18 is false.

3.5 Nested if Statements

A nested if statement is an if statement that is placed within another if statement. This is useful for making a series of dependent decisions.

Example:

int examScore = 85;
boolean isHonorsStudent = true;

if (examScore > 80)
{
   if (isHonorsStudent)
   {
      System.out.println("Congratulations! You made the honor roll!");
   }
}

In this case, the inner message will only be printed if both the examScore is greater than 80 AND the student is an isHonorsStudent.

3.6 Logical Operators

Logical operators are used to combine multiple Boolean expressions into a single expression.

Operator	Meaning
&&	AND
||	OR
!	NOT

• && (AND): The combined expression is true only if all of the individual expressions are true.
• || (OR): The combined expression is true if at least one of the individual expressions is true.
• ! (NOT): This operator reverses the value of a Boolean expression. If the expression is true, ! makes it false, and vice versa.

3.7 The Conditional Operator

The conditional operator (? :) is a concise way to write a simple if-else statement. It is a ternary operator because it requires three operands.

Syntax: booleanExpression ? valueIfTrue : valueIfFalse;

Example:

int age = 20;
String status = (age >= 18) ? "Adult" : "Minor";
System.out.println("Status: " + status);

This will assign the string "Adult" to the status variable because age >= 18 is true.

Chapter 3 Summary

• Boolean expressions are the core of decision-making, evaluating to true or false.
• The if statement executes a block of code only if its condition is true.
• The if-else statement provides two paths: one for a true condition and one for a false condition.
• Comparison operators (==, !=, >, <, >=, <=) are used to compare values.
• Logical operators (&&, ||, !) are used to combine or negate Boolean expressions.
• The conditional operator (? :) offers a shorthand for simple if-else logic.

Chapter Notes

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Chapter 4

More Object Concepts

Welcome to Chapter 4 of your Java Programming course! Having mastered the basics of classes, methods, and objects, we will now expand on these concepts. In this chapter, we will delve into more advanced object-oriented features that will allow you to write more efficient, organized, and robust code.

4.1 Understanding Blocks and Scope

In programming, a block is a segment of code that is contained within a pair of curly braces {}. The scope of a variable or method refers to the portion of a program where that variable or method is accessible. A variable's scope is determined by the block in which it is declared.

• A variable that is declared within a block is a local variable, and it can only be used within that block.
• Once a variable goes out of scope (for example, when the block it was declared in finishes executing), it can no longer be accessed.

Understanding scope is critical for preventing errors and writing clean, predictable code.

4.2 Overloading a Method

Overloading a method is the practice of writing multiple methods within the same class that share the same name but have different parameter lists. This allows you to use a single, meaningful identifier to perform similar, yet distinct, tasks.

To successfully overload a method, the parameter lists must satisfy at least one of these two conditions:

• The lists must have a different number of parameters.
• The lists must have parameters of different data types or the data types must be in a different order.

Overloading makes your code more readable and intuitive. For example, a computeArea() method could handle calculations for both a rectangle (two parameters) and a circle (one parameter).

4.3 Automatic Type Promotion in Method Calls

When you call an overloaded method, Java automatically promotes a data type to a larger, more inclusive data type if it's necessary to match a parameter in the method's parameter list. For example, a method call that passes a byte, short, or int to a method that expects a double parameter will work, because Java promotes the value to a double. This can save you from having to write an overloaded method for every possible numeric data type.

4.4 Learning About the this Reference

The this reference is a powerful tool in Java. Within any instance method or constructor, this is a keyword that refers to the object currently being created or used.

• You can use the this reference to pass an entire object to a method.
• More commonly, you can use this to make calls to overloaded constructors from within another constructor. This can make your code more efficient and reduce duplication.

4.5 Using static Fields

Some fields and methods can be shared by all objects of a class. These are declared using the static keyword.

• A static field, also known as a class-wide field, means that only a single copy of the variable exists in memory, no matter how many objects are created from the class. This is useful for data that is the same for all instances of a class, such as a constant value or a cumulative counter.
• A static method is also shared by all objects of a class and can be called without creating an object.

For example, a DogTriathlonParticipant class could have a static field named totalCumulativeScore to track the combined score of all participants, which is a single value that belongs to the class itself, not to any individual dog object.

4.6 Working with Prewritten Constants and Methods

The creators of Java have provided hundreds of prewritten classes that you can use in your programs. These are organized into packages.

• The java.lang package is automatically imported into every program you write. It contains fundamental classes, such as the System and Math classes.
• Other packages, such as java.util.Scanner or java.time.LocalDate, must be explicitly imported using an import statement.

The `Math` class, for example, is part of the `java.lang` package and provides useful methods for mathematical operations like finding the square root of a number or generating a random value. Similarly, the **`LocalDate` class** from the `java.time` package can be used to work with dates in your programs.

4.7 Understanding Composition

Composition is the principle of creating a class that contains objects of other classes as data fields. This models a "has-a" relationship. For instance, a Patient class might have a BloodData object as one of its fields. Composition is a powerful way to build complex programs by assembling smaller, more specialized objects.

Chapter 4 Summary

• Scope and Blocks: A variable's scope is limited to the block of code where it is declared.
• Method Overloading: Allows you to create multiple methods with the same name but different parameter lists, improving code readability.
• The this Reference: A keyword that refers to the current object, useful for passing the object itself or for efficient constructor chaining.
• static Members: Fields and methods declared with the static keyword belong to the class rather than to any specific object instance, and a single copy exists for all objects.
• Prewritten Classes: Java provides extensive libraries of prewritten classes in packages. The `java.lang` package is always available, while others must be explicitly imported.
• Composition: A method of building classes that contain objects of other classes as data fields, representing a "has-a" relationship.

Chapter Notes

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Chapter 5

Repetitive Tasks

Welcome to Chapter 5 of your Java Programming course! Having mastered the basics of classes, methods, and objects, we will now expand on these concepts. In this chapter, we will delve into more advanced object-oriented features that will allow you to write more efficient, organized, and robust code.

5.1 Understanding the Need for Loops

Imagine you need to print a message ten times, or process the scores of 100 students. You could write the same line of code over and over, but this is inefficient and prone to errors. A loop is a control structure that allows you to execute a statement or a block of statements repeatedly.

5.2 The while Loop

The while loop is a pretest loop, meaning its condition is checked before each iteration. The loop continues to execute as long as its Boolean expression evaluates to true.

Syntax:

while (BooleanExpression)
{
   // statements to repeat
}

Example:

int count = 0;
while (count < 5)
{
   System.out.println("Loop iteration: " + count);
   count++; // Increment the counter
}

This loop will print the message five times. The count++ statement is essential; without it, the loop would be an infinite loop because the condition count < 5 would never become false. An infinite loop is a common logical error that causes a program to run forever.

5.3 The for Loop

The for loop is a more compact way to write a loop, especially when you know exactly how many times you want the loop to iterate. It is also a pretest loop.

Syntax:

for (initialization; BooleanExpression; update)
{
   // statements to repeat
}

Example:

for (int i = 0; i < 5; i++)
{
   System.out.println("Loop iteration: " + i);
}

This for loop produces the exact same output as the previous while loop example.

5.4 The do-while Loop

The do-while loop is a posttest loop, meaning its condition is checked after the statements inside the loop have been executed. This guarantees that the loop will run at least once.

Syntax:

do
{
   // statements to repeat
} while (BooleanExpression);

Example:

int userChoice;
do
{
   System.out.println("Choose an option (1-3): ");
   userChoice = scanner.nextInt(); // Assume 'scanner' is a Scanner object
} while (userChoice < 1 || userChoice > 3);

This loop will always execute at least once, prompting the user for input, and will continue to loop until a valid choice is entered.

5.5 Nested Loops

Just like if statements, loops can be nested. A nested loop is a loop that is contained within another loop. This is useful for tasks like printing rows and columns or processing two-dimensional data.

Example:

for (int i = 0; i < 3; i++) // Outer loop
{
   for (int j = 0; j < 2; j++) // Inner loop
   {
      System.out.println("Outer loop: " + i + ", Inner loop: " + j);
   }
}

The inner loop will complete all its iterations for each single iteration of the outer loop.

5.6 Avoiding Common Pitfalls with Loops

• Infinite Loops: Always make sure that the condition that controls your loop will eventually become false.
• Off-by-One Errors: Be careful with your loop's start and end conditions (< vs. <= or starting at 0 vs. 1). An off-by-one error can cause a loop to execute one time too many or too few.

Chapter 5 Summary

• Loops are control structures that allow a block of code to be executed repeatedly.
• The while loop is a pretest loop that continues as long as its condition is true.
• The for loop is ideal for situations where the number of repetitions is known in advance.
• The do-while loop is a posttest loop that always executes at least once.
• Nested loops are used when you need to repeat a loop structure multiple times.
• Remember to avoid infinite loops and off-by-one errors to ensure your loops function correctly.

Chapter Notes

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Chapter 6

Handling Arrays

Welcome back, future Java developers! In our last chapter, we mastered the power of loops to handle repetitive tasks. Now, in Chapter 6, we'll learn about one of the most fundamental data structures in programming: arrays. Arrays allow you to store and manage multiple values of the same type in a single, organized structure.

6.1 Understanding What an Array Is

An array is a list of data items that all have the same type, such as a list of integers, characters, or even objects. Each element in the array is a variable, and all elements are referenced by a single name. You use an integer subscript or index to access an individual element within the array.

Key characteristics of an array:

• They are objects in Java.
• They are of a fixed size once they are created. You must specify the size when you create the array.
• The first element's index is 0, and the last element's index is size - 1.

6.2 Declaring and Initializing Arrays

There are a few ways to declare and initialize an array.

1. Declaring an array reference:

dataType[] arrayName;

Example: int[] studentScores;

2. Creating an array object and assigning it to the reference:

arrayName = new dataType[size];

Example: studentScores = new int[5];
This creates an array that can hold 5 integers, with each element initialized to its default value (e.g., 0 for int).

3. Declaring and creating in a single statement:

dataType[] arrayName = new dataType[size];

Example: double[] salesFigures = new double[10];

4. Initializing with a list of values:
You can also declare, create, and initialize an array all at once using an initializer list.

dataType[] arrayName = {value1, value2, value3, ...};

Example: String[] studentNames = {"Alice", "Bob", "Charlie"};
In this case, Java automatically determines the size of the array based on the number of values in the list.

6.3 Accessing Array Elements

To access an individual element in an array, you use its index inside square brackets [].

• Writing to an element:
  Example: studentScores[0] = 95;
• Reading from an element:
  Example: int firstScore = studentScores[0];

ArrayIndexOutOfBoundsException: If you try to access an element using an index that is outside the valid range (from 0 to array.length - 1), your program will crash with an ArrayIndexOutOfBoundsException. This is a common runtime error.

6.4 Using Loops with Arrays

Loops are almost always used to process arrays. They provide a simple and efficient way to iterate through every element.

Using a for loop to process all elements:

int[] numbers = {10, 20, 30, 40, 50};
int sum = 0;
for (int i = 0; i < numbers.length; i++)
{
   sum += numbers[i];
}
System.out.println("The sum is: " + sum);

The array.length property is a very useful tool that provides the number of elements in the array. It is a read-only field and is crucial for avoiding off-by-one errors.

Using the Enhanced for Loop:
The enhanced for loop (also known as the "for each" loop) is designed specifically to process every element in an array or collection. It is more concise but cannot be used to modify the elements of the array.

String[] names = {"Alice", "Bob", "Charlie"};
for (String name : names)
{
   System.out.println(name);
}

The loop reads, "For each String named name in the names array, do the following."

6.5 Handling Arrays of Objects

You can also create arrays that hold objects. For example, you can have an array of BankAccount objects or Student objects.

Example:

BankAccount[] accounts = new BankAccount[3];
accounts[0] = new BankAccount(1234, 500.0);
accounts[1] = new BankAccount(5678, 1200.0);

Notice that creating an array of objects only creates an array of references. You must then use new to create each individual object and assign it to an element in the array.

6.6 Parallel Arrays

Parallel arrays are two or more arrays with the same number of elements, where the elements in corresponding positions are logically related. For example, one array might hold student IDs, and a parallel array might hold their corresponding grades. This is a common way to organize related data.

Chapter 6 Summary

• An array is a fixed-size, ordered list of elements of the same data type.
• Array elements are accessed using an integer index starting from 0.
• You can declare, create, and initialize arrays using different syntaxes.
• The array.length property provides the number of elements in an array and is vital for controlling loops.
• Loops (especially the for loop) are the primary way to process all elements in an array. The enhanced for loop is a simpler way to read all elements.
• You can create arrays of objects, but each object must be instantiated individually.
• Parallel arrays are used to link related data across multiple arrays using corresponding indexes.

Chapter Notes

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Chapter 7

Characters, Strings, and the StringBuilder

Welcome to Chapter 7! In this chapter, we will dive into one of the most common and powerful data types in Java: the String. Strings are used everywhere in programming, from user input to file names, and mastering how to manipulate them is essential for any developer. We will also explore the different classes Java provides for working with character-based data efficiently.

7.1 Understanding String Data Problems

Handling text data can be more complex than working with primitive data types like integers or doubles. Strings are objects in Java, which means they come with their own set of rules for declaration, comparison, and manipulation. A common pitfall is forgetting that two string objects with the same content are not necessarily equal unless you use the correct comparison methods.

7.2 Using Character Class Methods

Java provides a useful wrapper class called Character that contains a number of static methods for working with individual characters. These methods are great for validating user input or performing checks on text. Some common methods include:

• isDigit(char ch): Checks if a character is a digit (0-9).
• isLetter(char ch): Checks if a character is a letter (a-z, A-Z).
• isUpperCase(char ch): Checks if a character is an uppercase letter.
• isLowerCase(char ch): Checks if a character is a lowercase letter.
• isWhitespace(char ch): Checks if a character is a whitespace character.

7.3 Declaring and Comparing String Objects

You can declare a String object in a few ways. The most common is a simple declaration and assignment, often using a string literal.

String name = "John Doe";

When comparing strings, you must use the equals() method, not the == operator. The == operator compares the memory addresses of the objects, not their content. The equals() method, however, compares the actual sequence of characters in the strings.

String name1 = "Alice";
String name2 = "Alice";
System.out.println(name1.equals(name2)); // This will be true
System.out.println(name1 == name2); // This might be false!

It's also important to be aware of empty strings and null strings. An empty string has a length of zero (""), while a null string has no value at all (null). Attempting to use a method on a null string will result in a NullPointerException.

7.4 Using a Variety of String Methods

The String class provides a rich set of methods for manipulating strings.

• charAt(int index): Returns the character at a specific index in the string. For example, "Hello".charAt(1) returns the character 'e'.
• length(): Returns the number of characters in the string.
• substring(int beginIndex, int endIndex): Returns a new string that is a substring of the original.
• indexOf(String str): Returns the index of the first occurrence of a specified substring.
• toLowerCase() and toUpperCase(): Returns a new string with all characters converted to lowercase or uppercase.
• startsWith(String prefix) and endsWith(String suffix): Checks if the string begins or ends with a specified prefix or suffix.

7.5 Converting String Objects to Numbers

Often, you will need to convert a string that contains digits into a numeric data type, such as an int or a double. Java's wrapper classes for primitive types (Integer, Double, etc.) contain static methods for this purpose. For example, Integer.parseInt(someString) will convert a string to an integer.

7.6 Learning About the StringBuilder and StringBuffer Classes

Strings in Java are immutable, meaning they cannot be changed after they are created. Every time you modify a string (e.g., by concatenating two strings), a new string object is created in memory. This can be inefficient when performing many modifications. The StringBuilder and StringBuffer classes were created to solve this problem by providing a mutable sequence of characters. For most common applications, StringBuilder is a good choice as it is not synchronized and therefore faster than StringBuffer.

Chapter 7 Summary

• Strings are Objects: Remember that in Java, strings are objects and should be compared using the equals() method, not the == operator.
• Character Class: The Character class provides helpful static methods for checking the properties of individual characters.
• String Methods: The String class has many methods for tasks like getting a character by index (charAt()), finding the length (length()), and converting case.
• Type Conversion: You can convert a string to a number using methods like Integer.parseInt().
• Mutable Strings: For situations involving frequent string modifications, use the more efficient StringBuilder or StringBuffer classes.

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Chapter 8

Arrays

Welcome to Chapter 8! In our last chapter, we learned about loops. Now, we will learn about one of the most fundamental data structures in programming: arrays. Arrays allow you to store and manage multiple values of the same type in a single, organized structure.

8.1 Declaring an Array

An array is a list of data items that all have the same type, such as a list of integers or objects. Each element in the array is referenced by an integer subscript or index. Arrays are objects in Java and are of a fixed size once they are created.

To declare an array reference, you use the following syntax:

dataType[] arrayName;

Example: int[] studentScores;

8.2 Initializing an Array

You can create an array object and assign it to the reference using the new keyword and specifying its size. The elements are initialized to their default values (e.g., 0 for int).

arrayName = new dataType[size];

You can also declare, create, and initialize an array all at once using an initializer list.

dataType[] arrayName = {value1, value2, value3, ...};

Example: String[] studentNames = {"Alice", "Bob", "Charlie"};

8.3 Using Variable Subscripts with an Array

To access an individual element in an array, you use its index inside square brackets [].

• Writing to an element:
  Example: studentScores[0] = 95;
• Reading from an element:
  Example: int firstScore = studentScores[0];

Attempting to access an element with an index outside the valid range (from 0 to array.length - 1) will result in an ArrayIndexOutOfBoundsException.

8.4 Using the Enhanced for Loop

Java's enhanced for loop provides a simpler way to cycle through all elements in an array without explicitly managing a loop control variable. It is also known as a "for each" loop.

for (String name : names)
{
   System.out.println(name);
}

8.5 Declaring and Using Arrays of Objects

You can also create arrays that hold objects. When you create an array of objects, you are creating an array of references. You must then use new to create each individual object and assign it to an element in the array.

8.6 Manipulating Arrays of Strings

Arrays of Strings are a common use case. For example, a program might prompt a user for a team name and then loop to accept a member's name for each position in the array.

8.7 Searching an Array and Using Parallel Arrays

Parallel arrays are two or more arrays with the same number of elements, where the elements in corresponding positions are logically related. For example, one array can hold discount range limits, and a parallel array can hold the corresponding discount rates.

int[] discountRangeLimits = {1, 13, 50, 100, 200};
double[] discountRates = {0, 0.10, 0.14, 0.18, 0.20};

You can then search for a value's appropriate category by performing a range match, comparing the value to the endpoints of numerical ranges to find where it belongs.

8.8 Passing Arrays to and Returning Arrays from Methods

Arrays can be passed as arguments to methods and can also be returned from methods. When an array is passed to a method, it is passed by reference, meaning the method can modify the original array.

Chapter 8 Summary

• An array is a fixed-size, ordered list of elements of the same data type, accessed using an integer index starting from 0.
• The array.length property provides the number of elements in an array.
• Loops (especially the for loop) are the primary way to process all elements in an array. The enhanced for loop is a simpler way to read all elements.
• You can create arrays of objects, but each object must be instantiated individually.
• Parallel arrays are used to link related data across multiple arrays using corresponding indexes.

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Chapter 9

Exception Handling

Welcome to Chapter 9 of your Java Programming course! So far, we've focused on writing code that works under ideal conditions. But what happens when something goes wrong? In this chapter, we will learn how to anticipate and handle errors gracefully using exception handling.

9.1 Understanding Exceptions

An exception is an object that is created when a method is unable to complete its task. Exceptions are not logical errors that you can fix with a change to your program's logic; they are events that disrupt the normal flow of a program's instructions. When a method encounters an exception, it throws the exception, and the program's normal execution halts. If the exception is not handled, the program terminates.

• Example: A file that your program is trying to read from is missing.

9.2 The try-catch Block

The fundamental way to handle an exception is by using a try-catch block.

• try block: A block of code that might throw an exception.
• catch block: A block of code that handles a specific type of exception. It is executed only if an exception is thrown in the try block.

Syntax:

try
{
   // Code that might throw an exception
}
catch (ExceptionType e)
{
   // Code to handle the exception
}

Example:

import java.util.Scanner;
public class Division
{
   public static void main(String[] args)
   {
      Scanner input = new Scanner(System.in);
      try
      {
         System.out.print("Enter a numerator: ");
         int numerator = input.nextInt();
         System.out.print("Enter a denominator: ");
         int denominator = input.nextInt();
         int result = numerator / denominator;
         System.out.println("Result: " + result);
      }
      catch (ArithmeticException e)
      {
         System.out.println("Cannot divide by zero.");
      }
   }
}

In this example, if the user enters 0 for the denominator, an ArithmeticException is thrown, and the catch block's code is executed instead of the program crashing.

9.3 Multiple catch Blocks

You can have multiple catch blocks to handle different types of exceptions that might be thrown in the try block. You should list catch blocks from most specific to most general.

Example:

try
{
   // Code that might throw an exception
}
catch (InputMismatchException e)
{
   System.out.println("Invalid input. Please enter a number.");
}
catch (ArithmeticException e)
{
   System.out.println("Cannot divide by zero.");
}
catch (Exception e)
{
   System.out.println("An unexpected error occurred.");
}

9.4 The finally Block

The finally block is an optional block that is always executed, regardless of whether an exception was thrown in the try block. It is typically used for cleanup tasks, such as closing files or database connections.

Syntax:

try
{
   // ...
}
catch (Exception e)
{
   // ...
}
finally
{
   // This code always runs
}

9.5 Throwing an Exception

You can manually throw an exception using the throw keyword. This is useful when you want to signal an error from your own code.

Syntax: throw new ExceptionType("Error message");

9.6 Creating Your Own Exception Class

You can create your own custom exception class by extending an existing exception class, such as Exception or RuntimeException. This allows you to create more specific and meaningful exceptions for your own applications.

Example:

public class MyCustomException extends Exception
{
   public MyCustomException(String message)
   {
      super(message);
   }
}

Chapter 9 Summary

• An exception is an object that signals an error or unusual event during program execution.
• The try-catch block is used to handle exceptions gracefully.
• You can have multiple catch blocks to handle different types of exceptions.
• The finally block always executes and is used for cleanup code.
• The throw keyword is used to manually throw an exception.
• You can create your own custom exception classes by extending a standard exception class.

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Chapter 10

Introduction to Inheritance

Welcome to Chapter 10! In this chapter, you will be introduced to one of the most important concepts in object-oriented programming: inheritance. Inheritance is a mechanism that allows you to create a new class by acquiring the behaviors and attributes of an existing class. This allows you to build new classes based on existing, tested ones, which saves time and reduces errors.

10.1 Learning About the Concept of Inheritance

Inheritance is a concept you are already familiar with from non-programming situations, such as genetics or family traits. Similarly, in object-oriented programming, classes can inherit data and methods from existing classes. When a class is created by inheriting from another, the new class automatically contains the data fields and methods of the original class.

Programmers use a graphical language called the Unified Modeling Language (UML) to describe classes and their relationships. In a UML diagram, an inheritance relationship is shown with an arrow that points from the descendant class to the original class.

The class that is used as a basis for inheritance is called a **base class**, **superclass**, or **parent class**. The class that inherits from a base class is called a **derived class**, **subclass**, or **child class**. A derived class always "is a(n)" case or example of the more general base class.

10.2 Extending Classes

In Java, you use the keyword extends to achieve inheritance. A derived class automatically receives the data fields and methods of its superclass, and you can then add new fields and methods to the subclass.

Inheritance is a one-way street: a child inherits from a parent, but not the other way around. A superclass object does not have access to its child’s data and methods because subclasses are more specific than the superclass they extend.

10.3 Overriding Superclass Methods

A subclass can override methods that it inherits from its superclass. This allows a subclass to provide a specific implementation of a method that is already defined in its superclass. When overriding a method, you can use the @Override tag to indicate that the method is intended to override a superclass method.

10.4 Calling Constructors During Inheritance

When you create a subclass object, the superclass's constructor is always called first. This ensures that the superclass is properly initialized before the subclass. You can use the super() keyword to explicitly call a superclass constructor, including those that require arguments.

10.5 Accessing Superclass Methods

You can use the super keyword to access methods and fields in the superclass from within the subclass. This is useful when you want to call the superclass's version of a method that you have overridden in the subclass.

10.6 Employing Information Hiding

Information hiding, or encapsulation, is a key principle in object-oriented programming. While a subclass inherits all fields and methods from its superclass, it can only directly access the public and protected members of the superclass. Private members are not directly accessible, but can be accessed through public methods provided by the superclass (e.g., `get` and `set` methods).

10.7 Methods You Cannot Override

There are certain methods that a subclass cannot override:

• static methods: A subclass cannot override a static method in its superclass.
• final methods: A subclass cannot override a method that is declared as final.
• Methods in a final superclass: A subclass cannot override any methods if the superclass itself is declared as final.

Chapter 10 Summary

• Inheritance: A mechanism for creating a new class from an existing one, saving development time and reducing errors.
• Terminology: A class that is inherited from is a superclass, while the new class is a subclass. The `is-a` relationship is key to understanding inheritance.
• Extending Classes: The `extends` keyword is used in Java to create an inheritance relationship.
• Overriding Methods: A subclass can provide its own implementation of a superclass method.
• Constructors: The superclass constructor is always called when a subclass object is created.
• Access: The `super` keyword provides access to superclass members.
• Restrictions: `static` and `final` methods cannot be overridden.

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Chapter 11

Recursion

Welcome to Chapter 11 of your Java Programming course! So far, we've used loops to handle repetitive tasks. Now, we'll explore an elegant and often more intuitive alternative for certain types of problems: recursion.

11.1 Understanding Recursion

A recursive method is one that calls itself, either directly or indirectly. The key to successful recursion is to have a defined base case, which is a condition that stops the recursion from running infinitely. Every recursive solution has two key components:

1. Base Case: A condition that causes the method to stop calling itself.
2. Recursive Call: The part of the method that calls itself, but with a different set of arguments that move the problem closer to the base case.

11.2 The Classic Example: Factorials

A classic example used to illustrate recursion is the calculation of a factorial. The factorial of a number n (written as n!) is the product of all positive integers less than or equal to n.

Recursive solution:

public static int factorial(int n)
{
   if (n <= 1)
   {
      return 1; // Base case
   }
   else
   {
      return n * factorial(n - 1); // Recursive call
   }
}

11.3 The Call Stack and Recursion

When a method is called, the computer places it on a data structure called the call stack. With recursion, each time a method calls itself, a new instance of that method is placed on top of the stack. An infinite recursion occurs when a recursive method never reaches its base case. This will eventually lead to a StackOverflowError.

11.4 The Fibonacci Sequence

The Fibonacci sequence is another great example for understanding recursion. Each number in the sequence is the sum of the two preceding ones.

Recursive solution:

public static int fibonacci(int n)
{
   if (n <= 1)
   {
      return n; // Base cases
   }
   else
   {
      return fibonacci(n - 1) + fibonacci(n - 2); // Recursive calls
   }
}

11.5 Advantages and Disadvantages of Recursion

Advantages:

• Elegance and Simplicity: For certain problems, a recursive solution can be much cleaner and easier to read than an iterative one.

Disadvantages:

• Performance Overhead: Each recursive call adds a new stack frame to the call stack, which can be slower and use more memory than a loop.
• Risk of StackOverflowError: Without a properly defined base case, you risk causing an infinite recursion and crashing your program.

Chapter 11 Summary

• Recursion is a technique where a method calls itself to solve a problem.
• Every recursive method must have a base case to prevent infinite recursion.
• The recursive call must move the problem closer to the base case.
• The call stack is used to manage the sequence of method calls.
• Failure to include a base case can lead to a StackOverflowError.

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Chapter 12

Advanced Arrays and ArrayLists

Welcome to Chapter 12 of your Java Programming course! We've already learned the fundamentals of arrays, which are a powerful tool for storing lists of data. In this chapter, we will take our understanding a step further by exploring more complex array structures and introducing a dynamic and flexible alternative: the ArrayList.

12.1 Understanding Multidimensional Arrays

A multidimensional array is an array of arrays. The most common type is a two-dimensional array, which can be thought of as a grid or a table with rows and columns.

• Declaration:

dataType[][] arrayName;

• Instantiation:

int[][] matrix = new int[3][4]; // 3 rows, 4 columns

You can use nested loops to process all elements in a multidimensional array.

Example:

for (int row = 0; row < matrix.length; row++)
{
   for (int col = 0; col < matrix[row].length; col++)
   {
      System.out.print(matrix[row][col] + " ");
   }
   System.out.println(); // Newline for the next row
}

12.2 Introducing ArrayList

The biggest limitation of a standard array is its fixed size. The ArrayList class, which is part of the java.util package, solves this problem by providing a resizable array implementation.

• Declaration and Creation:

import java.util.ArrayList;

ArrayList<String> names = new ArrayList<String>();

The <String> inside the angle brackets is a type parameter that specifies the type of objects the ArrayList will hold.

12.3 Key ArrayList Methods

You interact with an ArrayList using its methods.

• add(element): Adds an element to the end.
• get(index): Retrieves the element at a specific index.
• set(index, newElement): Replaces an element.
• remove(index): Removes an element.
• size(): Returns the number of elements.

12.4 Iterating Through an ArrayList

You can use a for loop or an enhanced for loop to process an ArrayList.

Enhanced for loop example:

for (String name : names)
{
   System.out.println(name);
}

12.5 ArrayList vs. Array

Feature	ArrayList	Array
Size	Dynamic (resizable)	Fixed
Access	Method calls (get, set)	Index operator ([])
Data Type	Can only hold objects	Can hold primitives and objects

Chapter 12 Summary

• Multidimensional arrays are arrays of arrays, useful for representing grids or tables.
• The ArrayList class provides a dynamic, resizable array for storing objects.
• You interact with an ArrayList using methods like add(), get(), set(), and remove().
• The size() method returns the number of elements in an ArrayList.
• ArrayLists are an excellent alternative to standard arrays when you need a list of a variable size.

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Chapter 13

File Input and Output

Welcome to the final chapter of your Java Programming course! In this chapter, you will learn how to handle file input and output, which allows your programs to store and retrieve data on a permanent basis. This is a crucial skill for any application that needs to save data between program runs.

13.1 Understanding Computer Files

A computer file is a collection of data stored on a nonvolatile device, such as a hard disk or a USB drive. Unlike data stored in variables (which use volatile storage like RAM), data in files is not lost when the computer loses power.

Files can be categorized as either:

• Text files: Contain data encoded using schemes like ASCII or Unicode, which can be read in a text editor. They can be data files (containing facts and figures) or program files (containing software instructions).
• Binary files: Contain data in binary format that cannot be understood by viewing them in a text editor. Examples include images, music, and compiled Java class files.

Each file has a path, which is a complete list of the disk drive and the hierarchy of directories where the file resides.

13.2 Using the Path and Files Classes

Java provides the java.nio.file package, which includes the Path and Files classes for working with files and directories.

• The Path class is used to create objects that contain information about files, such as their location and size.
• The Files class is used to perform operations on files and directories, such as deleting them or determining their attributes.

You can create a Path object using the Paths.get() method, which is a helper class that eliminates the need to create a FileSystem object first.

import java.nio.file.Paths;

Path path = Paths.get("C:\\Java\\Chapter.13\\SampleFile.txt");

A Path can be either absolute (a complete path that doesn't need any other information to locate a file) or relative (dependent on other path information).

13.3 File Organization, Streams, and Buffers

When you work with files, you use streams, which are objects that provide a connection to a file and allow you to perform input and output operations. Input streams are used to read data from a file, and output streams are used to write data to a file.

13.4 Using Java's IO Classes

The java.io package contains classes for performing file input and output. Some of the key classes include:

• FileWriter: Used to write character-based data to a file.
• FileReader: Used to read character-based data from a file.
• PrintWriter: Provides a convenient way to write formatted output to a text file.

13.5 Creating and Using Sequential Data Files

A sequential access file is a file where data is written and read from the beginning to the end, in a specific order. To access data, you must read all the records that precede it.

13.6 Learning About Random Access Files

In contrast to a sequential file, a random access file allows you to jump directly to any record in the file without reading the preceding records. This is useful for applications that need to quickly retrieve or update specific data records.

Chapter 13 Summary

• A computer file is a collection of data stored on a nonvolatile device.
• Files can be either text files or binary files.
• The Path and Files classes are used to work with files and directories.
• A stream is a flow of data, and buffers are used to temporarily hold data during input/output operations.
• Java provides classes in the java.io package for reading from and writing to files.
• Sequential access files are read from beginning to end.
• Random access files allow you to jump directly to any record.

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Final Chapter

Course Review and Final Test

Welcome to the final chapter of your Java Programming course! This chapter is designed as a comprehensive review to solidify all the concepts you've learned. Think of it as a final test that brings everything together, preparing you to apply your skills to real-world projects. You've come a long way, and this is your chance to see just how much you've learned.

Course Final Test

Select the correct answer for each question below. When you're finished, click "Submit Answers" to see your score.

1. What is a key advantage of the "write once, run anywhere" (WORA) capability in Java?

It allows Java code to be written and compiled for a specific operating system. It eliminates the need for a compiler, as the code is interpreted directly. It allows Java bytecode to run on any machine with a JVM, regardless of the operating system. It ensures that all Java programs are free of syntax errors.

2. Which of the following is an example of a primitive data type?

String Array int Object

3. How should you compare the content of two String objects?

Using the == operator Using the equals() method Using the compareTo() method Strings cannot be compared

4. What is a key feature of the do-while loop?

It is a pretest loop. It is ideal for iterating a known number of times. Its condition is checked after the loop's body executes, guaranteeing at least one run. It can only be used with arrays.

5. In Java, what is the first index of an array?

1 The size of the array 0 The value of the first element

6. What is the purpose of the try-catch block?

To create a new method. To handle exceptions and prevent a program from crashing. To define a loop that executes at least once. To ensure a block of code is always executed, regardless of errors.

7. What is the key characteristic of inheritance in OOP?

A class can have multiple methods with the same name. A class can acquire the attributes and behaviors of another class. A class's data and methods are contained within a single unit. An object's methods can be used without knowing the low-level details of how they are executed.

8. What is the purpose of the static keyword?

To make a variable a constant. To declare a variable that is shared by all objects of a class. To make a method private. To make a method non-overridable.

9. What is a base case in a recursive method?

The first line of code in the method. The last line of code in the method. A condition that prevents the method from calling itself again, stopping the recursion. The part of the method that calls itself.

10. What is the primary advantage of using an ArrayList over a standard array?

It can store primitive data types. Its size is dynamic and can be changed after creation. It can be accessed using a single index. It can only store String objects.

11. A single copy of a variable that exists no matter how many objects of a class are created is known as a...

Local variable Instance variable Static field Constant

12. What does a NullPointerException indicate?

An attempt to divide by zero. A failure to convert a String to a number. An attempt to use a method on a null string. Accessing an array element that is out of bounds.

13. Which loop is a posttest loop, guaranteeing its code block will execute at least once?

for loop while loop do-while loop Nested loop

14. The practice of writing multiple methods within the same class that share the same name but have different parameter lists is called...

Method overriding Method encapsulation Method overloading Method recursion

15. What does the final keyword do when applied to a method?

It prevents the method from being called. It means the method's return type cannot be changed. It prevents a subclass from overriding the method. It ensures the method can only be accessed by its own class.

16. What is the role of the super keyword?

To call the constructor of the current class. To refer to the superclass of the current object. To prevent a method from being overridden. To declare a variable as a constant.

17. What is an `ArrayIndexOutOfBoundsException`?

An exception that is thrown when a program tries to divide by zero. An exception that is thrown when you try to access an element using an index that is outside the valid range of the array. An exception that is thrown when a file is not found. An exception that is thrown when a string cannot be converted to a number.

18. Which of the following is an immutable class?

ArrayList StringBuilder String Array

19. What is the key to preventing an infinite recursion?

Using a for loop. Using a try-catch block. Having a well-defined base case. Declaring all variables as final.

20. In an inheritance relationship, which class is more specific?

The superclass The parent class The base class The subclass

21. What is the purpose of the finally block in exception handling?

It is executed only if an exception is thrown. It is executed only if no exception is thrown. It is a block that always executes, regardless of whether an exception was thrown. It is used to declare a custom exception.

22. What is a "stream" in the context of file I/O?

A type of variable that stores file data. An object that provides a connection to a file for input or output. A method for closing a file after it's used. A way to permanently store data in RAM.

23. What is the primary function of the Path class?

To delete files. To create a file stream. To contain information about a file, such as its location. To write data to a file.

24. When is a method's scope limited to a block of code?

When it's a static method. When it's a local variable. When it's a final method. A method's scope is never limited to a block of code.

25. What is the purpose of the @Override tag?

To indicate a new method. To indicate that a method is intended to override a superclass method. To prevent a method from being overridden. To create a static method.

26. What does composition model in object-oriented programming?

A "has-a" relationship. An "is-a" relationship. An "is-like-a" relationship. A "uses-a" relationship.

27. Which class is commonly used for converting a String object to a number?

String Number Scanner A wrapper class, like Integer or Double.

28. What is a multidimensional array?

An array that can hold different data types. An array that can change its size. An array of arrays, useful for representing grids or tables. An array that holds only primitive data types.

29. Which of the following is an example of a logical error?

Forgetting a semicolon at the end of a statement. Using a variable that was not declared. Creating an infinite loop. A misspelling of a keyword.

30. What is a nonvolatile storage device?

A device where data is lost when the power is turned off, like RAM. A device where data is saved permanently, like a hard disk. A device that requires a continuous electrical charge to maintain its data. A device that processes data streams in a sequential order.

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