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Previous Year Question (PYQs)

What is the output of the following JAVA program?

public class Good {
private int m;

public Good(int m) {
this.m = m;
}

public Boolean equals(Good n) {
return n.m == m;
}

public static void main(String args[]) {
Good m1 = new Good(22);
Good m2 = new Good(22);
Object s1 = new Good(22);
Object s2 = new Good(22);

System.out.println(m1.equals(m2));
System.out.println(s1.equals(s2));
System.out.println(m1.equals(s2));
System.out.println(s1.equals(m2));
}





Solution

Here, the class has a method

$equals(Good\ n)$

This method does not override the original $equals(Object)$ method of Java because the parameter type is $Good$, not $Object$.

For Line 1:

$m1.equals(m2)$

Here both are objects of class $Good$, so $equals(Good\ n)$ is called.

Both values are $22$, so output is

$True$

For Line 2:

$s1.equals(s2)$

Here $s1$ and $s2$ are declared as $Object$ type.

So, Java calls $Object$ class $equals()$ method, which compares references.

Since both are different objects, output is

$False$

For Line 3:

$m1.equals(s2)$

Here $s2$ is of type $Object$, so $equals(Good\ n)$ is not called.

It calls $equals(Object)$, so reference comparison is done.

Output is

$False$

For Line 4:

$s1.equals(m2)$

Here $s1$ is of type $Object$, so again $Object$ class $equals()$ method is called.

Output is

$False$

Therefore, output is:

$True,\ False,\ False,\ False$


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