Interfaces and Abstract Classes MCQs with Answers 2027

Q21

Open question

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

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Q22

Open question

In Java, can an abstract class have constructors?

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Q23

Open question

What is the result of the following code snippet?

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

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Q24

Open question

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

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Q25

Open question

What is the result of the following code snippet?

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

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Q26

Open question

In Java, can an abstract class have private methods with implementations?

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Q27

Open question

What is the result of the following code snippet?

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

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Q28

Open question

In Java, can an abstract class have static methods with implementations?

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Q29

Open question

What is the result of the following code snippet?

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

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Q30

Open question

In Java, can an abstract class have default methods with implementations?

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Q31

Open question

Given the following piece of code:

public class School{
        public abstract double numberOfStudent();
}

which of the following statements is true?

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Q32

Open question

Which of the following class definitions defines a legal abstract class?

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Q33

Open question

Which of the following declares an abstract method in an abstract Java class?

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Q34

Open question

Which of the following statements regarding abstract classes are true?

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Q35

Open question

Suppose A is an abstract class, B is a concrete subclass of A, and both A and B have a default constructor. Which of the following is correct?
1. A a = new A();
2. A a = new B();
3. B b = new A();
4. B b = new B();

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Q36

Open question

Which of the following is a correct interface?

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Q37

Open question

Determine output of the following code.

interface A { }

class C { }

class D extends C { }

class B extends D implements A { }

public class Test extends Thread{
        public static void main(String[] args){
                B b = new B();
                if (b instanceof A)
                        System.out.println("b is an instance of A");
                if (b instanceof C)
                        System.out.println("b is an instance of C");
        }
}

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Q38

Open question

Given the following piece of code:

public interface Guard{
        void doYourJob();
}
abstract public class Dog implements Guard{ }

which of the following statements is correct?

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Q39

Open question

In Java, declaring a class abstract is useful

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Q40

Open question

What will be the output?

interface A{
	public void method();
}
class One{
	public void method(){
		System.out.println("Class One method");
	}
}
class Two extends One implements A{
	public void method(){
		System.out.println("Class Two method");
	}
}
public class Test extends Two{
	public static void main(String[] args){
		A a = new Two();
		a.method();		
	}
}

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