Skimpy OOP: Introduction to Object-Oriented Programming Using Java

11. Stuff That’s Tacked on the End

Sample answers to Check Yourself Before You Wreck Yourself (on the assignments) questions

These review questions are intended to be a little open-ended, so your answers will vary. Many of the sample answers in this section are adapted from responses generated by Copilot in early 2025, using the web interface. Unfortunately, I didn’t take careful notes on which responses I used as I was experimenting with Copilot and only expected to use the material as a placeholder until I wrote my own. It turned out that the Copilot responses were pretty good.

Getting Started Chapter

What does JDK stand for?

Java Development Kit
What is an example of an Integrated Development Environment?

Visual Studio Code, eclipse, IntelliJ, and many others.

Computers and Coding

What is the primary role of a programming language in the context of computer programming?

The primary role of a programming language is to act as a bridge between human language and machine language. It allows humans to write instructions in a way that is easier for them to understand and use, which can then be accurately translated into machine language that a computer can execute.
Explain the difference between compiled and interpreted programming languages. Provide an example of each.
- Compiled languages are those where the source code is translated into machine language by a compiler before the program is run. This machine language file can then be executed directly by the computer. An example of a compiled language is C.
- Interpreted languages are those where the source code is translated into machine language on the fly, as the program is running, by an interpreter. An example of an interpreted language is Python.
- Java is a unique case as it is both compiled and interpreted. The source code is first compiled into an intermediate language called bytecode, which is then interpreted by the Java Runtime Environment (JRE) at runtime.
Describe the basic structure of a simple Java program, such as the "Hello World" example provided in the chapter.
- A simple Java program, like the "Hello World" example, consists of:
- Class declaration: This defines the class, which is a blueprint for objects. In the example, the class is named HelloWorld.
- main() method: This is the entry point of the program where execution begins. It is declared as public static void main(String[] args).
- println() statement: This is used to output text to the console. In the example, System.out.println("Hello World!"); prints "Hello World!" to the console.
- Code blocks: These are enclosed in curly braces {} to define the scope of the class and the main method.
What are the key steps in the software development process as outlined in the chapter? Why is it important to follow these steps?
- The key steps in the software development process are:
- Analysis: Identifying the goals and scope of the program. This step ensures that you understand what the program needs to do.
- Testing Plan: Determining how the final program will be tested. This step ensures that you have a clear understanding of how to verify that the program works correctly.
- Implementation: Writing and testing the code iteratively. This step involves developing the program piece by piece, testing each part to ensure it works before moving on to the next.
- Revise or Maintain: Updating the program as needed based on changing requirements or ensuring it continues to perform as expected over time.
- Following these steps is important because it helps keep the development process organized and focused, ensures efficient use of time, and makes complex programming tasks more approachable.

Variables

What is the difference between a constant and a variable in Java? Provide an example of each.
- A constant is a piece of data that cannot change during program execution. It is declared using the final keyword and must be assigned a value when it is declared. For example:
  1 final double SALES_TAX_RATE = 8.7;
- A variable is a piece of data that can change (or "vary") during program execution. It is declared by specifying a data type and an identifier, and can be assigned different values throughout the program. For example:
  1 2 int age = 21; age = 22; // The value of age can be changed

Explain the purpose of the Scanner class in Java and provide an example of how it is used to get user input.

The Scanner class in Java is used to get input from the user through the keyboard. It provides methods to read different types of input, such as strings, integers, and doubles. To use the Scanner class, you need to import it and create an instance of the class. Here is an example:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17 import java.util.Scanner;

public class InputDemo {
  public static void main(String[] args) {
    Scanner input = new Scanner(System.in);
    String name;
    int age;

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

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

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

Describe the difference between integer division and floating-point division in Java. Why is it important to be aware of this distinction?
- Integer division in Java occurs when both operands are integers. The result is also an integer, and any fractional part is truncated (i.e., discarded). For example:
  1 int result = 10 / 3; // result is 3, not 3.33
- Floating-point division occurs when at least one of the operands is a floating-point number (e.g., float or double). The result is a floating-point number, and the fractional part is preserved. For example:
  1 double result = 10.0 / 3; // result is 3.333333...
- It is important to be aware of this distinction because using integer division when you expect a floating-point result can lead to incorrect calculations and unexpected behavior in your programs.

What are compound assignment operators in Java? Provide examples of how they are used in arithmetic operations.

Compound assignment operators in Java are shorthand ways of writing common arithmetic operations that update the value of a variable. They combine an arithmetic operator with the assignment operator (=). Here are some examples:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14 int x = 5;
x += 3; // Equivalent to x = x + 3; x is now 8

int y = 10;
y -= 2; // Equivalent to y = y - 2; y is now 8

int z = 4;
z *= 2; // Equivalent to z = z * 2; z is now 8

int a = 20;
a /= 4; // Equivalent to a = a / 4; a is now 5

int b = 15;
b %= 6; // Equivalent to b = b % 6; b is now 3

Methods

What is the main purpose of using methods in Java, and how do they contribute to code maintainability?

The main purpose of using methods in Java is to organize code into reusable blocks that perform specific tasks. Methods help in breaking down complex programs into smaller, manageable pieces, making the code easier to read, understand, and maintain. By encapsulating functionality within methods, changes can be made in one place without affecting other parts of the program. This improves maintainability because if a bug is found or a change is needed, it can be addressed within the method itself, rather than having to update multiple instances of the same code throughout the program.
Explain the difference between a parameter and an argument in the context of Java methods. Provide an example to illustrate your explanation.

In Java, a parameter is a variable defined in the method declaration that acts as a placeholder for the value that will be passed to the method. An argument, on the other hand, is the actual value that is passed to the method when it is called. For example, in the method definition public static void printArea(double radius), radius is a parameter. When the method is called with printArea(5.0), the value 5.0 is the argument passed to the method.
Why is it generally better to return values from methods rather than printing them directly within the method? How does this practice improve the modularity and reusability of code?

It is generally better to return values from methods rather than printing them directly within the method because returning values allows the method to be more versatile and reusable. When a method returns a value, it can be used in various contexts, such as in calculations, assignments, or further processing, without being tied to a specific output format. This practice improves modularity by keeping the method focused on a single task (e.g., performing a calculation) and leaving the decision of how to use the result to the calling code. It also enhances reusability, as the method can be used in different parts of the program or even in different programs without modification.

Classes and Objects

What is the primary difference between procedural programming and object-oriented programming (OOP)?

Procedural programming organizes programs as a collection of tasks or methods that need to be performed in a specific order. In contrast, OOP organizes programs as a collection of interacting objects, each representing a real-world entity with attributes (data) and behaviors (methods).
Explain the concept of a class and how it relates to objects in OOP.

A class is a blueprint or template for creating objects. It defines the attributes and behaviors that the objects created from the class will have. An object is an instance of a class, meaning it is created with the fields and methods implemented in the class.
What is encapsulation, and why is it important in OOP? Provide an example.

Encapsulation is the concept of hiding the internal state of an object and requiring all interaction to be performed through the object’s methods. This is important because it protects the object’s data from unintended or harmful modifications. For example, in a bank account class, the balance field is private and can only be accessed or modified through a public getter method, and modified through public deposit and withdraw methods.

Decisions

Explain what Boolean expressions are and how they are used to make decisions in Java.

Boolean expressions are statements that evaluate to either true or false. In Java, they are used to make decisions by determining which blocks of code to execute based on the evaluation of these expressions.
Explain the difference between a relational operator and a logical operator.

Relational operators compare two values and determine their relationship, such as equality (==), inequality (!=), less than (<), and greater than (>). Logical operators, on the other hand, combine multiple Boolean expressions to form a single, more complex expression, such as AND (&&), OR (||), and NOT (!).
What is the difference between an if statement and an if-else statement?

An if statement allows you to execute a block of code only if a certain condition is true. An if-else statement extends this by providing an alternative block of code to execute if the condition is false, allowing you to choose between two possible actions.
How can you write code that runs one code block from multiple options?

You can use a switch statement to run one code block from multiple options based on the value of an expression. Alternatively, you can use an if-else if structure to chain multiple if-else statements together, allowing you to handle more than two options.

Loops

Describe the difference between a while loop and a do-while loop.

A while loop checks the condition before executing the block of code, meaning the code might not execute at all if the condition is false initially. A do-while loop, on the other hand, checks the condition after executing the block of code, ensuring that the code is executed at least once.
What is a control variable, and how is it used in loops?

A control variable is a variable used to control the execution of a loop. It is typically initialized before the loop starts, checked in the loop’s condition to determine whether the loop should continue, and updated within the loop to eventually meet the condition that stops the loop.
Give an example of an indefinite loop.

An example of an indefinite loop is a program that asks the user to guess a number and keeps prompting the user until they guess correctly. The loop repeats until the user’s input matches the target number. Another example is a loop that reads user input until a specific sentinel value is entered, indicating the end of input.

Debugging and Generative AI

What is the difference between a compile-time error and a runtime error?

Compile-time errors occur when the compiler cannot translate the source code into machine code due to syntax or semantic issues. These errors must be fixed before the program can run. Runtime errors, on the other hand, occur during the execution of the program and are often due to logic errors, causing the program to behave unexpectedly or crash.
How can using output statements help in debugging a program?

Output statements, such as print() statements, allow you to monitor the values of variables and the flow of execution in your program. This visibility helps you pinpoint where things are going wrong, making it easier to identify and correct errors.
What are some strategies you can use when you’re frustrated by a bug in your code?

When you’re frustrated by a bug in your code, take a break to clear your mind and return with fresh eyes. Use output statements to track variables and execution flow, clean up your code for better readability, and break down the problem into smaller parts. If needed, seek help from others and stay patient, knowing that debugging is a valuable part of the learning process.

Arrays

What is an array and how does it differ from a single variable?

An array is a data structure that allows you to store multiple pieces of data in a single collection. Unlike a single variable, which can only store one piece of data at a time, an array can hold multiple values, each of which is referred to as an element. Each element in an array is accessed using its unique index, which starts at 0 for the first element and increments by 1 for each subsequent element.
What is an ArrayIndexOutOfBoundsException and when does it occur?

An ArrayIndexOutOfBoundsException is a runtime error that occurs when you try to access an element at an index that is outside the bounds of the array. This means you are trying to access an index that is either less than 0 or greater than or equal to the length of the array. For example, if an array has 10 elements, valid indices are 0 through 9. Attempting to access the element at index 10 or higher will result in this exception.

How can loops be used to traverse an array? Provide an example of a for loop that sums the elements of an integer array.

Loops can be used to traverse an array by iterating through each element, performing operations such as reading, modifying, or accumulating values. Here is an example of a for loop that sums the elements of an integer array:

1
2
3
4
5
6 int[] scores = {90, 85, 95, 88, 92};
int sum = 0;
for (int i = 0; i < scores.length; i++) {
    sum += scores[i];
}
System.out.println("The sum of the scores is " + sum);

In this example, the for loop iterates through each element of the scores array, adding each element’s value to the sum variable. After the loop completes, the total sum of the array elements is printed.

Inheritance

What is inheritance in object-oriented programming, and what are its benefits

Inheritance is a feature in object-oriented programming that allows a class (subclass) to inherit attributes and methods from another class (superclass), promoting code reuse and organization by enabling the creation of hierarchical relationships between classes.
How do you override a method in a subclass, and why might you want to do this?

To override a method in a subclass, you define a method in the subclass with the same name, return type, and parameters as the method in the superclass. This allows the subclass to provide a specific implementation of the method, which can be used to customize or extend the behavior of the inherited method.
Explain how to use the super keyword in a constructor.

The super keyword is used in a subclass constructor to call the constructor of its superclass. This must be the first statement in the subclass constructor and is used to ensure that the superclass is properly initialized before the subclass adds its own initialization code. For example: super(parameter1, parameter2);.
Explain how different subclasses can be managed in a single array.

Different subclasses can be managed in a single array by declaring the array to be of the type of their common superclass. This allows the array to hold instances of any subclass, enabling polymorphism. For example, an array of type BankAccount can hold instances of both CheckingAccount and SavingsAccount, and common methods can be called on these instances through the superclass reference.

Swing GUIs

What is a Graphical User Interface (GUI) and why is it important for end users?

A Graphical User Interface (GUI) is a type of user interface that allows users to interact with electronic devices using graphical elements such as windows, icons, and buttons, rather than text-based commands. It is important for end users because it makes software more accessible and easier to use, especially for those who are not familiar with command-line interfaces.
Explain the role of the Swing library in Java and why it is preferred for beginners over JavaFX.

The Swing library in Java provides a set of pre-built GUI components that developers can use to create graphical user interfaces. It is preferred for beginners over JavaFX because it is simpler to use, does not require additional installations, and the concepts learned in Swing can be easily transferred to JavaFX.
Describe the process of creating a simple GUI using Swing, including the main components involved.

To create a simple GUI using Swing, you start by importing the necessary Swing classes, then instantiate a JFrame object to serve as the main window. You can set attributes like the title and size of the window, and add other components such as JLabel, JButton, and JTextField to the frame. Finally, you make the frame visible by calling the setVisible(true) method.
What is event-driven programming in the context of GUIs, and how does it differ from console-based programming?

Event-driven programming in the context of GUIs involves writing code that responds to user actions, such as clicking a button or entering text. This is different from console-based programming, where the program runs sequentially from top to bottom and waits for user input at specific points. In event-driven programming, the program continuously listens for events and executes the corresponding event handlers when an event occurs.