Inheritence -Java Programming MCQ Questions and Answers

31

Which is true?

A) "X extends Y" is correct if and only if X is a class and Y is an interface B) "X extends Y" is correct if and only if X is an interface and Y is a class C) "X extends Y" is correct if X and Y are either both classes or both interfaces D) "X extends Y" is correct for all combinations of X and Y being classes and/or interfaces

Discuss

Answer & Solution

Answer: Option C

Solution:

A is incorrect because classes implement interfaces, they don't extend them. B is incorrect because interfaces only "inherit from" other interfaces. D is incorrect based on the preceding rules.

32

Which of the following is true?
1. A class can extend more than one class.
2. A class can extend only one class but many interfaces.
3. An interface can extend many interfaces.
4. An interface can implement many interfaces.
5. A class can extend one class and implement many interfaces.

A) 1 and 2 B) 2 and 4 C) 3 and 5 D) 3 and 4 E) 2 and 5

Discuss

Answer & Solution

Answer: Option C

No explanation is given for this question. Let's Discuss on Board

33

What is the result of compiling and running the following code?

class Base{
        public Base(){
                System.out.print("Base");
        }
}
public class Derived extends Base{
        public Derived(){
                this("Examveda");
                System.out.print("Derived");
        }
        public Derived(String s){
                System.out.print(s);
        }
        public static void main(String[] args){
                new Derived();
        }
}

A) ExamvedaDerived B) ExamvedaBaseDerived C) BaseExamvedaDerived D) ExamvedaDerivedBase E) Compilation Error

Discuss

Answer & Solution

Answer: Option C

Solution:

1. new Derived(); statement executes and invoke the non-parametrized constructor of derived class i.e.
public Derived();
2. As Derived class is a subclass of class Base so super(); executes and calls the super class constructor and prints "Base".
3. After that
this("Examveda"); executes and call the parametrized constructor
public Derived(String s); of Derived class as this always refer to the current object. So, it prints "Examveda".
4. Lastly the print statement executes and prints "Derived"
Hence output is BaseExamvedaDerived.

34

What is the output of the following program code?

abstract class C1{
	public C1(){ 
		System.out.print(1); 
	} 
} 
class C2 extends C1{ 
	public C2(){ 
		System.out.print(2); 
	} 
} 
class C3 extends C2{ 
	public C3(){ 
		System.out.println(3); 
	} 
} 
public class Test{ 
	public static void main(String[] a){ 
		new C3(); 
	} 
}

A) 12 B) 23 C) 123 D) 321

Discuss

Answer & Solution

Answer: Option C

No explanation is given for this question. Let's Discuss on Board

35

The concept of multiple inheritance is implemented in Java by
I. Extending two or more classes.
II. Extending one class and implementing one or more interfaces.
III. Implementing two or more interfaces.

A) Only (II) B) (I) and (II) C) (II) and (III) D) Only (I) E) Only (III)

Discuss

Answer & Solution

Answer: Option C

No explanation is given for this question. Let's Discuss on Board

36

What will be the output?

interface A{
	public void method1();
}
class One implements A{
	public void method1(){
		System.out.println("Class One method1");
	}
}
class Two extends One{
	public void method1(){
		System.out.println("Class Two method1");
	}
}
public class Test extends Two{
	public static void main(String[] args){
		A a = new Two();
		a.method1();
	}
}

A) Compilation Error B) Class One method1 C) Class Two method1 D) Throws a NoSuchMethodException at runtime. E) None of these

Discuss

Answer & Solution

Answer: Option C

No explanation is given for this question. Let's Discuss on Board

37

What is the result of compiling and running this program?

class Mammal{
      void eat(Mammal m){
            System.out.println("Mammal eats food");
      }
}
class Cattle extends Mammal{
      void eat(Cattle c){
            System.out.println("Cattle eats hay");
      }
}
class Horse extends Cattle{
      void eat(Horse h){
            System.out.println("Horse eats hay");
      }
}
public class Test{
      public static void main(String[] args){
            Mammal h = new Horse();
            Cattle c = new Horse();
            c.eat(h);
      }
}

A) prints "Mammal eats food" B) prints "Cattle eats hay" C) prints "Horse eats hay" D) Class cast Exception at runtime. E) None of these

Discuss

Answer & Solution

Answer: Option A

No explanation is given for this question. Let's Discuss on Board

38

Determine output:

class A{
	public void method1(){
		System.out.print("Class A method1");
	}
}
class B extends A{
	public void method2(){
		System.out.print("Class B method2");
	}
}
class C extends B{
	public void method2(){
		System.out.print("Class C method2");
	}	
	public void method3(){
		System.out.print("Class C method3");
	}
}
public class Test{
	public static void main(String args[]){
		A a = new A();
		C c = new C();		
		c.method2();
		a = c;
		a.method3();
	}
}

A) Class B method2 Class C method3 B) Class C method2 Class C method3 C) Compilation Error D) Runtime exception E) None of these

Discuss

Answer & Solution

Answer: Option C

Solution:

It is important to understand that it is the type of reference variable - not the type of the object that it refers to - that which determines what members can be accessed. That is, when a reference to a subclass object is assigned to a super class reference variable, we will have access only to those parts of the object defined by the superclass.
In the above program method method3() is defined in the class C which is a subclass of B and so A. Even the reference variable a refers to c, a can't access method3() as this method is unknown to class A.

39

What will be printed after executing following program code?

class Base{
	int value = 0;
        Base(){
        	addValue();
        }
        void addValue(){
        	value += 10;
        }
        int getValue(){
        	return value;
        }
}
class Derived extends Base{
	Derived(){
		addValue();
	}
	void addValue(){
		value +=  20;
	}
}
public class Test{
	public static void main(String[] args){
		Base b = new Derived();
		System.out.println(b.getValue());
	}
}

A) 30 B) 10 C) 40 D) 20 E) None of these

Discuss

Answer & Solution

Answer: Option C

Solution:

When object of new derived is called, the flow goes to Derived() first, by default super(); is present in Derived() as the first statement, so the flow now goes to Base. Here value is initialised to 0 and then addValue() is called. The addValue has been overridden in Derived() hence The Base's addValue() will perform value+20(0+20) .After this control flows back to Derived()'s addValue() where again value+20 is done (20+20). Hence Answer is 40

40

What will be the output?

class Parent{
      public void method(){
            System.out.println("Hi i am parent");
      }
}
public class Child extends Parent{
      protected void method(){
            System.out.println("Hi i am Child");
      }
      public static void main(String args[]){
            Child child = new Child();
            child.method();
      }
}

A) Compiles successfully and print B) Run Time error C) Compile time error D) None of These

Discuss

Answer & Solution

Answer: Option C

Solution:

We cannot reduce the visibility of the inherited method from super class. If the overridden or hidden method is public, then the overriding or hiding method must be public; otherwise, a compile-time error occurs. If the overridden or hidden method is protected, then the overriding or hiding method must be protected or public; otherwise, a compile-time error occurs. If the overridden or hidden method has default (package) access, then the overriding or hiding method must not be private; otherwise, a compile-time error occurs.