Why does every object in Java implicitly extend java.lang.Object class?

Question

I have been programming in Java for quite some time, but when I tried to explain what an java.lang.Object class is to a friend, I could not come up with more than a simple one-liner:

All objects in Java extend java.lang.Object implicitly

I was not quite sure why it should do so.

So, I looked upon the source code on GrepCode, hoping that I can find some clues. Now I know what a java.lang.Object is and what it does, I want to know if there was any specific reason as to why it was designed this way.

My question still prevails: why should every object extend java.lang.Object?

Answer 1

I would say that the reason is to have a common API for all objects in java to supports basic functionality like

• synchronization - wait, notify, notifyAll
• garbage collection - finalize
• collection support - hashCode, equals
• object cloning - clone

And every object

• has a class it belongs to - getClass
• can represent itself as a string, because we are humans and can read strings - toString