Intermediate quizzes – Java casting object

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 Object Casting

Quiz 1: Casting objects in Java

What will happen if you try to compile and execute the main method?

public class MySuper {

	protected int i = 3;

	public MySuper() {
		i ++ ;
		System.out.print("-x" + method(5));
	}
	public int method(){
		return i + i;
	}
	public int method(int i){
		return method() + i;
	}
}

public class MySub extends MySuper {

	int i = 4;

	public int method(){
		return i * i + super.i;
	}
	public static void main(String[] args){
		MySuper mySuper = new MySuper();
		MySuper Mysub = new MySub();
	}
}

Select the correct answer.

a. Illegal at compile time.

b. Illegal at run time

c. This code writes "-x13-x9" to the standard output.

d. This code writes "-x13-x13" to the standard output.

e. This code writes "-x11-x11" to the standard output.

f. This code writes "-x13-x24" to the standard output.

g. This code writes "-x13-x25" to the standard output.

h. This code writes "null" to the standard output.

i. This code writes nothing to the standard output.

Quiz 2: Upcasting and downcasting objects in Java

What happens when the following program is compiled and run?

public class Super {

	protected int x = 3;

	public int method(){
		return x + 5;
	}
	public int method(int x){
		return method() + x;
	}
}

public class Sub extends Super {

	int x = 7;

	public int method(){
		return x * 4 + super.x;
	}
	public static void main(String[] args){
		Super s = new Sub();
		Sub su = (Sub) s;
		Super sup = new Super();
		System.out.print("-" + s.x + "-" + s.method(3) 
                                 + "-" + su.x + "-" + sup.method(3));
	}
}

Select the correct answer.

a. Illegal at compile time.

b. Illegal at run time

c. This code writes "-3-11-7-11" to the standard output.

d. This code writes "-7-34-7-11" to the standard output.

e. This code writes "-3-34-3-11" to the standard output.

f. This code writes "-3-34-7-11" to the standard output.

g. This code writes "-7-34-3-11" to the standard output.

h. This code writes "null" to the standard output.

i. This code writes nothing to the standard output.

Article: Java casting object Quizzes: Beginner  Intermediate  Advanced

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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.

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