This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Agree with Mohammed earlier. You want a JDialog, which disappears after use. Much better than trying to create two frames and dispose of the second.
Actually, you can probably use the setDefaultCloseOperation method on the frame, with DISPOSE_ON_CLOSE, so the dispose() call may be unnecessary.