This keyword usage in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print the current object's name using this keyword.

Java

public class Person {
    String name;
    public Person(String name) {
        this.name = name;
    }
    public void printName() {
        System.out.println([1].name);
    }
}

Drag options to blanks, or click blank then click option'

Aobj

Bsuper

Cself

Dthis

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'super' instead of 'this' to access current object's fields.

Using undefined variable names like 'self' or 'obj'.

The this keyword refers to the current object instance. To access the instance variable name, use this.name.

2fill in blank

medium

Complete the constructor to call another constructor in the same class using this keyword.

Java

public class Box {
    int width, height;
    public Box() {
        this(10, 20);
    }
    public Box(int width, int height) {
        this.width = width;
        this.height = height;
    }
    public void printSize() {
        System.out.println("Width: " + width + ", Height: " + height);
    }
}

Drag options to blanks, or click blank then click option'

Aself

Bsuper

Cthis

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'super' to call constructors in the same class.

Calling constructor after other statements.

The this keyword can be used to call another constructor in the same class. Here, this(10, 20); calls the parameterized constructor.

3fill in blank

hard

Fix the error by completing the code to correctly refer to the instance variable value when parameter name is the same.

Java

public class Counter {
    int value;
    public void setValue(int value) {
        [1].value = value;
    }
}

Drag options to blanks, or click blank then click option'

Athis

Bsuper

CCounter

Dself

Attempts:

3 left

💡 Hint

Common Mistakes

Using parameter name directly causing assignment to itself.

Using 'super' or class name incorrectly.

When parameter name shadows instance variable, use this to refer to the instance variable explicitly.

4fill in blank

hard

Fill both blanks to complete the method that returns the current object's string representation using this keyword.

Java

public class Point {
    int x, y;
    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }
    public String toString() {
        return "Point(" + [1].x + ", " + [2].y + ")";
    }
}

Drag options to blanks, or click blank then click option'

Athis

Bsuper

Cself

Dobj

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'super' which refers to parent class.

Using undefined variables like 'self' or 'obj'.

The this keyword refers to the current object. Use it to access instance variables x and y inside the toString method.

5fill in blank

hard

Fill all three blanks to complete the constructor chaining and instance variable assignment using this keyword.

Java

public class Rectangle {
    int width, height;
    public Rectangle() {
        this([1], [2]);
    }
    public Rectangle(int width, int height) {
        [3].width = width;
        this.height = height;
    }
}

Drag options to blanks, or click blank then click option'

A10

B20

Cthis

Dsuper

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'super' instead of 'this' for constructor chaining.

Assigning instance variables without 'this' when shadowed.

The no-argument constructor calls the parameterized constructor with values 10 and 20 using this(10, 20);. Inside the parameterized constructor, this is used to assign the instance variable width.