This week's book giveaway is in the Performance forum. We're giving away four copies of The Java Performance Companion and have Charlie Hunt, Monica Beckwith, Poonam Parhar, & Bengt Rutisson on-line! See this thread for details.
Using JFrame I have opened a new window, used obj.setVisible(true) to bring to the top. Later minimized the opened window manually and after sometimes, I tried to bring to the top(visible) again through code using obj.setVisible(true), Now it opens another window instead of opening the minimized window.
You code is wrong. You are creating a new Window and the setVisible(true) method is showing the new window. Don't create a new window, instead you need to keep a reference to the existing window. I know nothing about the structure of your code so I can't suggest how you do this.