The following Java exercise(s) are designed for beginner level programmers. If the level is too hard, then I recommend reading my article about this topic, which offers a theoretical explanation including more exercises. Read More: Java Abstract Classes

Article: Java abstract classes
Quizzes: Beginner Intermediate Advanced

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Quiz 1: Extending an abstract class

What happens when the following program is compiled and run?

public abstract class MyAbstract {

	abstract int getSum();
	abstract int getSum(int x);
	abstract int getSum(int x, int y);
}

public abstract class Sub extends MyAbstract {

	int x = 4;

	int getSum(){
		return x + x;
	}
	int getSum(int x){
		return x + x;
	}
	int getSum(int x, int y){
		int z = x + y;
		System.out.print(z);
		return z;
	}
	public static void main(String[] args){
		Sub sub = new Sub();
		sub.getSum(4,2);
	}
}

Quiz 2: Abstract classes in Java

What happens when the following program is compiled and run?

public abstract class AbstractClass {

	int b = 6;

	abstract int getNumber(int c, int d);
}

public class Sub extends AbstractClass {

	int b = 2;

	Sub() {
		b = super.b;
	}
	int getNumber(int x, int y){
		int i = x - y + b;
		System.out.print(i);
		return i;
	}
	public static void main(String[] args){
		Sub sub = new Sub();
		sub.getNumber(7,3);
	}
}

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Article: Java abstract classes
Quizzes: Beginner Intermediate Advanced

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Sar Maroof is graduated from HBO Amsterdam "higher professional education". He is a professional computer programming teacher, gives master classes and publishes technical articles. His experience with developing software started from 2001 and he has worked as a software developer for several big as well as small companies and later as a freelancer. He is the author of Java quizmaster and Build a Java application in 7 days.