Sorting Objects

Making some good progress with bubbleSort. And now I am on the last assignment, that is bubbleSorting objects. And this leaves me to a question that always leaves me dumbfounded, how do we compare objects? I know that Strings are objects, and for Strings we compare them by their unicode value for their character, but what about an object? It's like saying how to compare two people. Is there a standardized way of doing this? Well, it's just my paradigm of thinking, which I should ditch because it's doing no good.