hash codes for classes that do not implement the hashCode() method

[Rachel Glenn]

Suppose I have a class called Dog, as follows:

class Dog{
    public Dog();
public int a;
public int b;

}

This class does not implement the hashCode() method.

Is it guaranteed then that all instances of Dog will produce unique hash codes (that I assume are generated by the java run time) ?

[Matthew Brown]

There's no guarantee they'll be unique. Thing about this: you can create more objects than there are int values, in which case you'd have to have duplicate hash codes. But there's a good chance that they will be distinct.