Is there a sample project somewhere with simple code that would show me how to put together a very simple IDE kind of thing? For example, I would like to be able to create objects on a screen (Canvas?) and drag them around on the screen.
It may not be quite what you're looking for, but the NetBeans Platform provides a framework for doing this sort of thing. You might like to have a look at the paint program that is one of the supplied code samples.
You could program it from scratch using the standard Java Platform, but it wouldn't be "simple"... it would be long and complicated, and there's no need to re-invent the wheel.
I'm not sure but I think Eclipse has something similar, based around SWT (an alternative to Swing that uses native widgets).