Why interfaces are used in Java - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare an interface named Vehicle.

Java

public interface [1] {
    void move();
}

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AVehicle

BCar

CDrive

DMoveable

Attempts:

3 left

💡 Hint

Common Mistakes

Using a class name instead of an interface name.

Forgetting to use the 'interface' keyword.

The keyword interface is used to declare an interface, and Vehicle is the interface name.

2fill in blank

medium

Complete the code to make class Car implement the Vehicle interface.

Java

public class Car [1] Vehicle {
    public void move() {
        System.out.println("Car is moving");
    }
}

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Ainherits

Bextends

Cimplements

Duses

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'extends' instead of 'implements' for interfaces.

Omitting the 'implements' keyword.

In Java, a class uses the implements keyword to adopt an interface.

3fill in blank

hard

Fix the error in the code by completing the interface method declaration.

Java

public interface Animal {
    [1] sound();
}

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Avoid

Bpublic

Cint

DString

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'void' when a return value is expected.

Omitting the return type.

Interface methods must declare a return type. Here, sound() returns a String describing the sound.

4fill in blank

hard

Fill both blanks to create a map that maps words to their lengths only if length is greater than 3.

Java

Map<String, Integer> wordLengths = words.stream()
    .filter(word -> word.length() [1] 3)
    .collect(Collectors.toMap(word -> word, word -> word.[2]()));

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A>

Blength

C<

Dsize

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the filter.

Using 'size()' instead of 'length()' for strings.

The filter keeps words with length greater than 3 using >. The method length() gets the length of the word.

5fill in blank

hard

Fill all three blanks to create a map of uppercase keys to values only if value is negative.

Java

Map<String, Integer> filteredMap = data.entrySet().stream()
    .filter(entry -> entry.getValue() [1] 0)
    .collect(Collectors.toMap(entry -> entry.getKey().[2](), entry -> entry.[3]()));

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A<

BgetValue

CgetKey

DtoUpperCase

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'getKey()' instead of 'getValue()' for values.

Using '>' instead of '<' in the filter.

The filter keeps entries with value less than 0 using '<'. The key is converted to uppercase with toUpperCase(). The value is accessed with getValue().