[haridharna]

Hello,
I am hari a resident of india.
I have been to this form many times. but this is my first posting.

I have a little confusion with the remove method of Set and HashSet.
Can any one tell me how does this method work exactly.
See the code and the result given below. I am confused aboud when the hashcode and the equals methods will be called.

Code:

import java.util.*;

class KeyMaster {
	public int i;

	public KeyMaster(int i) {
		this.i = i;
	}

	public boolean equals(Object o) {
		System.out.println("equal:"+ (i == ((KeyMaster) o).i));
		return i == ((KeyMaster) o).i;
	}

	public int hashCode() {
		System.out.println("Hashcode:"+i);
		return i;
	}
	
	public String toString() {
		return ""+i;
	}
}

public class MapIt {
	public static void main(String[] args) {
		Set<KeyMaster> set = new HashSet<KeyMaster>();
		KeyMaster k1 = new KeyMaster(1);
		KeyMaster k2 = new KeyMaster(2);
		set.add(k1);
		set.add(k2);
		
		k1.i=2;
		set.remove(k1);
		System.out.println(set.contains(k2));
		System.out.println(set);
	}
}

The ouput for the above code is :
Hashcode:1
Hashcode:2
Hashcode:2
equal:true
Hashcode:2
false
[2]

Code:

public class MapIt {
	public static void main(String[] args) {
		Set<KeyMaster> set = new HashSet<KeyMaster>();
		KeyMaster k1 = new KeyMaster(1);
		KeyMaster k2 = new KeyMaster(2);
		set.add(k1);
		set.add(k2);
		
	//	k1.i=2;
		set.remove(k1);
		System.out.println(set.contains(k2));
		System.out.println(set);
	}
}

if we comment the k1.i=2 the following is the output.
Hashcode:1
Hashcode:2
Hashcode:1
Hashcode:2
true
[2]
---------------

Code:

public class MapIt {
	public static void main(String[] args) {
		Set<KeyMaster> set = new HashSet<KeyMaster>();
		KeyMaster k1 = new KeyMaster(1);
		KeyMaster k2 = new KeyMaster(2);
		set.add(k1);
		set.add(k2);
		
		k1.i=2;
		set.remove(k1);
		System.out.println(set.contains(k1));
		System.out.println(set.contains(k2));
		System.out.println(set);
	}
}

for the above code the following is the output:

Hashcode:1
Hashcode:2
Hashcode:2
equal:true
Hashcode:2
false
Hashcode:2
false
[2]

I am confused with when the equals method will be called and why the contains method is giving false.