Advanced quizzes – Java abstract classes

The following Java exercise(s) are designed for intermediate level programmers. If the level is too hard, then I recommend to select an easier one or you might consider reading my article about this topic, which offers a theoretical explanation including more exercises. Read More: Java Abstract Classes

Quiz 1: Overwriting abstract methods

What is written to the standard output as the result of executing the following code?

public abstract class Base {

	int x = 3;

	public Base() {
		x += 2;
		System.out.print("-x" + x);
		x ++ ;
	}
	abstract int calculate();
	abstract int calculate(int i);
}

public class SuperA extends Base {

	int x = 1;

	public SuperA() {
		System.out.print("-x" + calculate(2));
	}
	int calculate(){
		return x;
	}
	int calculate(int i){
		return(calculate() + i);
	}
}

public class Sub extends SuperA {

	Sub() {
		x += 3;
	}
	int calculate(){
		return x + 6;
	}
	public static void main(String[] args){
		Sub sub = new Sub();
		System.out.print("-x" + sub.calculate());
	}
}

Select the correct answer.

a. Illegal at compile time.

b. Illegal at run time

c. This code writes “-x3-x10” to the standard output.

d. This code writes “-x5-x9-x10” to the standard output.

e. This code writes “-x5-x3-x10” to the standard output.

f. This code writes “-x5-x3-x7” to the standard output.

g. This code writes “-x5-x9-x7” to the standard output.

h. This code writes “null” to the standard output.

i. This code writes nothing to the standard output.

Quiz 2: Extending an abstract class in Java

What appears in the standard output when this program is invoked?

public abstract class Base {

	int y = 5;

	public Base() {
		y -= 2;
		System.out.print("-y" + method(4,7));
	}
	abstract int method(int i);
	abstract int method(int i, int i2);
}

public class Super extends Base {

	int y = 2;

	public Super() {
		System.out.print("-y" + method(4));
	}
	int method(int i){
		return(y * i + super.y);
	}
	int method(int i, int i2){
		return(method(i) + i + i2);
	}
}

public class Sub extends Super {

	int method(int i){
		return y * 2 + i;
	}
	public static void main(String[] args){
		Sub sub = new Sub();
	}
}

Select the correct answer.

a. Illegal at compile time

b. Illegal at run time

c. This code writes “-y22-y11” to the standard output.

d. This code writes “-y19-y12” to the standard output.

e. This code writes “-y8” to the standard output.

f. This code writes “-y15-y8” to the standard output.

g. This code writes “-y13” to the standard output.

h. This code writes “null” to the standard output.

i. This code writes nothing to the standard output.

Article: Java abstract classes Quizzes: Beginner  Intermediate  Advanced

    Suggested Articles



• Advanced quizzes – Java nested classes
• Advanced quizzes – Java final classes and variables
• Beginner quizzes – Java abstract classes
• Intermediate quizzes – Java abstract classes exercises
• Advanced quizzes – Java classes and objects
• Java abstract classes using practical exercises

Sar Maroof is a professional software development teacher, gives master classes and publishes technical articles. He is also an expert software developer and worked for several big as well as small companies and later as a freelancer.

Subscribe to Sar Maroof's RSS feeds!  Mail this page to a friend!  Bookmark this page!

Facebook

Twitter

Reddit

Linkedin