Dear Aaron,
The
java contract for hashCode() says that if equals() method returns true for comparison on two objects then the hashCode() for both should return the same value. However it does not ensure that for different runs of the same program the hascode returned should be same.
For example suppose hascode returned x on Monday and equals returns true. Then on Tuesday if the same program runs then if the equals method returns true then they both objects will should return the same hashcode but not necessarily x.
This is from javadoc of java.lang.Object
The general contract of hashCode is:
--Whenever it is invoked on the same object more than once during an execution of a Java application, the hashCode method must consistently return the same integer, provided no information used in equals comparisons on the object is modified. This integer need not remain consistent from one execution of an application to another execution of the same application.
--If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.
--It is not required that if two objects are unequal according to the equals(java.lang.Object) method, then calling the hashCode method on each of the two objects must produce distinct integer results. However, the programmer should be aware that producing distinct integer results for unequal objects may improve the performance of hashtables.
For more information please go through the javadoc of Object class
enjoy!!!
rahul
