hashCode() contract

[jomypgeorge]

Hi friends

i have a confusion regarding hashCode() contract
the rule says if equals() return true then hashCode() comparison should also return true

but i violate this but no problem in compiling and running

class HashCodeTest1
{
int x;
int y;
HashCodeTest1(int x, int y)
	{
	this.x = x;
	this.y = y;
	}
public boolean equals(Object o)
	{
	if (this.x == ((HashCodeTest1)o).x)
		return true;
	return false;
	}
public int hashCode()
	{
	return y;
	}
public static void main(String ... args)
	{
	HashCodeTest1 obj1 = new HashCodeTest1(10,10);
	HashCodeTest1 obj2 = new HashCodeTest1(10,20);
	System.out.println(obj1.equals(obj2));
	System.out.println(obj1.hashCode() == obj2.hashCode());
	}
}

why this code works fine?
is hashCode() contract is just a specification which is not mandatory?

thanks in advance......

[Fubarable]

why this code works fine?
is hashCode() contract is just a specification which is not mandatory?

Correct. Disobeying this "rule" will not cause a compiler error (indeed there is no way that the compiler could possibly check for all possible infarctions of this rule), but will create a program that can potentially misbehave in pernicious and difficult to detect ways. Disobey this rule at your own peril.

[Tolls]

If you had a HashMap that used one of those objects as a key you might see problems.
For example:

Map<HashCodeTest1, String> map = new HashMap<HashCodeTest1, String>();
HashCodeTest1 myKey = new HashCodeTest1(1,0);
HashCodeTest1 myEqualKey = new HashCodeTest1(1,1);
map.put(myKey, "Something or other");
if (myKey.equals(myEqualKey)) {
    // Should be able to use myEqualKey to get the value in the map since they're equal
    System.out.println(map.get(myEqualKey));  // Uh oh, this is null
}

[jomypgeorge]

thanks to all for quick replys