Can somebody let me know what is the difference between setSelectionInterval and addSelectionInterval with example?

How to change default background color in Swing?

suppose i have 4 JFrames in my project and i want to use single JDialog for all the JFrames, in such situation i have to pass the current JFrame class ie "this" keyword , the problem to receive different reference in the same class in different JFrames.
I have already tried by using Object class ,but it was not acceptedmy be through abstract classes or interfaces

A) B) C) D)

A) line 1, 2, 3B) line 8, 9C) line 3, 4, 5D) line 8, 9, 10