Interfaces and Abstract Classes -Java Programming MCQ Questions and Answers

1.

Given the following piece of code:

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

which of the following statements is true?

A. The keywords public and abstract cannot be used together.

B. The method numberOfStudent() in class School must have a body.

C. You must add a return statement in method numberOfStudent().

D. Class School must be defined abstract.

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2.
Which of the following class definitions defines a legal abstract class?

A. class A { abstract void unfinished() { } }

B. class A { abstract void unfinished(); }

C. abstract class A { abstract void unfinished(); }

D. public class abstract A { abstract void unfinished(); }

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3.
Which of the following declares an abstract method in an abstract Java class?

A. public abstract method();

B. public abstract void method();

C. public void abstract Method();

D. public void method() {}

E. public abstract void method() {}

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4.
Which of the following statements regarding abstract classes are true?

A. An abstract class can be extended.

B. A subclass of a non-abstract superclass can be abstract.

C. A subclass can override a concrete method in a superclass to declare it abstract.

D. An abstract class can be used as a data type.

E. All of the above

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5.
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();

A. 1 and 2

B. 2 and 4

C. 3 and 4

D. 1 and 3

E. 2 and 3

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Interfaces and Abstract Classes -Java Programming MCQ Questions and Answers

1. Given the following piece of code: public class School{ public abstract double numberOfStudent(); } which of the following statements is true?

Answer & Solution

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

Answer & Solution

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

Answer & Solution

4. Which of the following statements regarding abstract classes are true?

Answer & Solution

5. 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();

Answer & Solution

1.
Given the following piece of code:

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

which of the following statements is true?

2.
Which of the following class definitions defines a legal abstract class?

3.
Which of the following declares an abstract method in an abstract Java class?

4.
Which of the following statements regarding abstract classes are true?

5.
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();