Gang Liu

To better understand what an inner class is, I'd suggest reading Sun's Java Tutorial Trail on Inner Classes.

Thanks for the reminding and answer!
I have read this tutorial before. The answer of my question can not be found directly from the tutorial.
Actually I want to ask why in this if statement the outter class name Test4 can be used to refer to the flag. How can you know you can use this format to refer to a outter class's field variable? In which book or in which part of the sun tutorial can you find similar usage like Test4.this.flag(I can not find a example like this in Sun's inner class tutorial)?

I am not sure about the meaning of "Test4" in the if statement: Test4.this.flag.
Could anybody give some hint?