Interfaces and Abstract Classes -Java Programming MCQ Questions and Answers

11

In Java, can an interface have private methods with implementations?

A) Only if the methods are marked as "static" B) Only if the methods are marked as "final" C) Yes, starting from Java 9, interfaces can have private methods D) No, interfaces cannot have private methods

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Answer & Solution

Answer: Option C

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12

What is the result of the following code snippet?

interface MyInterface {
    void myMethod();
}
public class MyClass implements MyInterface {
    public void myMethod() {
        System.out.println("Implementation");
    }
    public static void main(String[] args) {
        MyInterface obj = new MyClass();
        obj.myMethod();
    }
}

A) Compilation error B) Runtime exception C) MyClass D) Implementation

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Answer & Solution

Answer: Option D

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13

In Java, can an abstract class extend another class?

A) No, abstract classes cannot extend other classes B) Yes, abstract classes can extend both abstract and concrete classes C) Only if the superclass is marked as "static" D) Only if the subclass is marked as "final"

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Answer & Solution

Answer: Option B

Solution:

In Java, abstract classes can extend both abstract and concrete classes.

When an abstract class extends another class (whether abstract or concrete), it inherits the properties and methods of that class.

An abstract class is allowed to inherit from a concrete class and can override or use the methods from the superclass.

Option A is incorrect because abstract classes can extend other classes.

Option C is incorrect since there is no requirement for the superclass to be marked as "static."

Option D is incorrect as the subclass does not need to be marked "final" to extend a class.

14

What is the purpose of the "extends" keyword in Java?

A) To mark a class as abstract B) To declare a method C) To implement an interface D) To create a subclass

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Answer & Solution

Answer: Option D

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15

In Java, can an interface extend another interface?

A) No, interfaces cannot extend other interfaces B) Only if both interfaces have the same methods C) Yes, an interface can extend multiple interfaces D) Only if the interface is marked as "private"

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Answer & Solution

Answer: Option C

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16

What is the result of the following code snippet?

abstract class MyAbstract {
    abstract void myMethod();
}
class MyClass extends MyAbstract {
    void myMethod() {
        System.out.println("Implementation");
    }
    public static void main(String[] args) {
        MyAbstract obj = new MyClass();
        obj.myMethod();
    }
}

A) Runtime exception B) Implementation C) MyClass D) None of these

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Answer & Solution

Answer: Option B

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17

In Java, can an abstract class have non-abstract methods?

A) Only if the abstract methods are marked as "static" B) Only if the non-abstract methods are marked as "private" C) Yes, an abstract class can have both abstract and non-abstract methods D) No, abstract classes can only have abstract methods

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Answer & Solution

Answer: Option C

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18

What is the purpose of the "default" keyword in Java interfaces?

A) To mark a method as abstract B) To create a new interface C) To declare a class D) To specify the default implementation of a method

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Answer & Solution

Answer: Option D

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19

What is the result of the following code snippet?

interface MyInterface {
    default void myMethod() {
        System.out.println("Default Implementation");
    }
}
class MyClass implements MyInterface {
    public static void main(String[] args) {
        MyInterface obj = new MyClass();
        obj.myMethod();
    }
}

A) Default Implementation B) Compilation error C) Runtime exception D) MyClass

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Answer & Solution

Answer: Option A

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20

In Java, can a class implement an interface and extend an abstract class simultaneously?

A) Only if the class is marked as "final" B) Only if both the interface and abstract class have the same methods C) No, it is not allowed D) Yes, a class can implement an interface and extend an abstract class

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Answer & Solution

Answer: Option D

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