Why create "new Object()"

Question

Why would anyone want to create a Object?
Object obj = new Object();
I've seen people use it during synchronization locks but why create a new object instead of any other alternatives?
synchronized(obj) {
Are there any other uses for Object?

Answer 1

This is one of the most usual use for new Object() that I've come across - it's used to provide something to lock against that can be shared between various instances. An Object instance is considered lightweight (ie, the minimal thing you can lock against) and it doesn't imply that it will be used in your code for anything else (since it doesn't do much else).
You're right that there are other alternatives (often overlooked), such as synchronising on a Class instance (this.getClass() or MyClass.class) - this is at least guaranteed to exist and therefore its being lightweight doesn't really matter. But it's not always appropriate, especially if you've got various levels of locking going on. As usual, you've got to choose what best suits your own situation and your own personal style.
Another use for an Object instance is to provide an enumeration of constants whose value isn't important:
public class MyLayoutManager implements LayoutManager
  public static final Object NORTH = new Object();
  public static final Object SOUTH = new Object();
}I'm not suggesting that my example is ideal (personally I'd choose a constant whose toString at least made sense for debugging) but it does demonstrate how you can use an Object to provide constants for use by other bits of code (or even internally, say as keys into a Map) - they simply do something like MyLayoutManager.NORTH to indicate something to my code.
Clearly there are other uses for Object (such as being the base class for everything) and providing default implementations of hashCode, equals and all the locking stuff. But I can't think of any other uses of an Object instance that I've had before. No doubt other people have come across some...
Hope this helps.