AP Computer Science A: Constructor Worksheet with Answer Key

📚 Topic Summary

In AP Computer Science A, constructors are special methods used to initialize objects of a class. They have the same name as the class and are invoked when an object is created using the new keyword. Constructors ensure that the object's instance variables are properly set up with initial values. Understanding constructors is crucial for creating well-behaved and predictable objects.

A class can have multiple constructors with different parameter lists (constructor overloading), allowing for flexibility in object initialization. If a class does not define any constructors, a default (no-argument) constructor is automatically provided by the compiler. However, if you define at least one constructor, the default constructor is no longer automatically provided.

🧠 Part A: Vocabulary

Match the term with its definition:

Answer Key:

✏️ Part B: Fill in the Blanks

Complete the following paragraph using the words: new, instance, class, constructor, object.

A ___________ is a template for creating __________. When we create an __________ of a __________, we use the keyword __________ followed by a call to the __________. This special method initializes the __________ variables of the __________.

Answer:

A class is a template for creating objects. When we create an instance of a class, we use the keyword new followed by a call to the constructor. This special method initializes the instance variables of the object.

🤔 Part C: Critical Thinking

Explain the importance of constructors in object-oriented programming and provide an example of a scenario where constructor overloading would be beneficial.

Answer:

Constructors are crucial in object-oriented programming because they ensure that objects are properly initialized when they are created. Without constructors, objects might start in an inconsistent or undefined state, leading to unpredictable behavior. Constructors allow us to set initial values for instance variables, perform necessary setup tasks, and enforce constraints on the object's state.

Constructor overloading is beneficial when we want to provide different ways to initialize an object. For example, consider a Rectangle class. We might want to create a rectangle with a specified width and height, or we might want to create a square by specifying only the side length. Constructor overloading allows us to define multiple constructors, each with a different set of parameters, to handle these different initialization scenarios. For instance:

public class Rectangle {
    private int width;
    private int height;

    // Constructor to create a rectangle with specified width and height
    public Rectangle(int width, int height) {
        this.width = width;
        this.height = height;
    }

    // Constructor to create a square with specified side length
    public Rectangle(int side) {
        this.width = side;
        this.height = side;
    }
}