Default methods in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a default method in an interface.

Java

public interface MyInterface {
    default void [1]() {
        System.out.println("Default method");
    }
}

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

Avoid

Bdefault

CdefaultMethod

Dmethod

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'default' as the method name causes a syntax error.

Omitting the method name entirely.

The method name should be defaultMethod. The keyword default is already used before the return type.

2fill in blank

medium

Complete the code to call the default method from an interface inside a class.

Java

public class MyClass implements MyInterface {
    public void callDefault() {
        [1].super.defaultMethod();
    }
}

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

Ainterface

BMyInterface

Cthis

Dsuper

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'super' alone causes a compile error.

Using 'this' does not call the interface default method.

To call a default method from an interface, use InterfaceName.super.methodName(). Here, MyInterface.defaultMethod() is incorrect; it should be MyInterface.super.defaultMethod(), but since the blank is before the dot, the correct choice is MyInterface to complete the call.

3fill in blank

hard

Fix the error in the code to correctly override a default method in a class.

Java

public class MyClass implements MyInterface {
    @Override
    public void [1]() {
        System.out.println("Overridden method");
    }
}

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

Adefaultmethod

Bdefault_method

CDefaultMethod

DdefaultMethod

Attempts:

3 left

💡 Hint

Common Mistakes

Changing the case of the method name causes it not to override.

Adding underscores or other characters changes the method signature.

The method name must exactly match the default method name in the interface, which is defaultMethod with correct case.

4fill in blank

hard

Fill both blanks to define a default method with a return type and a return statement.

Java

public interface Calculator {
    default int [1](int a, int b) {
        return a [2] b;
    }
}

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

Aadd

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using subtraction or multiplication operator instead of addition.

Using a method name that does not match the operation.

The method name is add and the operator to add two numbers is +.

5fill in blank

hard

Fill all three blanks to implement a default method that checks if a number is even.

Java

public interface NumberCheck {
    default boolean [1](int num) {
        return num [2] 2 [3] 0;
    }
}

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

AisEven

B%

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' causes incorrect logic.

Using wrong method names or operators.

The method name is isEven. The modulo operator % checks the remainder, and == compares it to zero to determine evenness.