hashCode and equals

[Sherman Hung]

Why the following statements are false?
1. If the reference x and y denote two different objects, then the expression x.equals(y) is false.
2. If the reference x and y denote two different objects, then the expression (x.hashCoce() == y.hashCode()) is false.

[Brian Glodde]

1. They are 2 different objects, therefore 2 different references. Not equal. From the JavaDocs equals() definition: "Indicates whether some other object is *equal to* this one."
2. It is true the hashCode() values are different.
Code:

public class ReferenceTest
{
public static void main( String args[] )
{
Object o1 = new Object();
Object o2 = new Object();

System.out.println( "Object to object comparisons using equals: " + o1.equals( o2 ) );
System.out.println( "Object comparison using hash code: " + ((o1.hashCode()) == (o2.hashCode())) );
System.out.println( " ---- " );
System.out.println( "Object 1 hashCode(): " + o1.hashCode() );
System.out.println( "Object 2 hashCode(): " + o2.hashCode() );
}

}

[Joshua Kueck]

If reference x and y are of type Object, then x.equals(y) is equivalent to x==y. This will compare the references. However, if reference x and y are of some type that Overrides equals (most do), then it usually compares the actual objects to one another.

[Joshua Kueck]

public class EqualsTest{
Integer x = new Integer(5);
Integer y = new Integer(5);
Object xo = new Object();
Object yo = new Object();
public void testMe ()
{
System.out.println(x.equals(y)); //prints true
System.out.println(x==y); //prints false
System.out.println(xo.equals(yo));//prints false
System.out.println(xo==yo);//prints false
}
public static void main (String[] args)
{
new EqualsTest().testMe();
}
}
  

[andy lau]

does the hashCoce() return an object referance???

[Brian Glodde]

Andy, Try compiling the code example I posted, it'll write out the hashCode(). Also, the JavaDocs are a good source of this type of information. In short, hashCode() does just what it says, returns a hash value for the object for use in data structures such as a hashtable.