How to determine the hash code value for an object if the hashCode method has not been overridden?

If the hashCode() method is not overridden in a class, the default implementation from the Object class is used. In this implementation, the hash code is usually based on the internal address of the object in memory (or some unique identifier associated with the object), which ensures uniqueness for each instance within a single program run.

That is, without overriding hashCode(), different objects (even with the same fields) will have different hash codes, and the same object will always have the same hash code.

Example:

Object obj = new Object();
int hash = obj.hashCode();
System.out.println(hash); // Will output a number related to the object's address