I want to make a JButton object on a JFrame to be the default button for the form. That means the button should be always selected by default and when the user hits 'enter' the button should be activated (pressed).
Any idea how to achieve this?
The concept you need to use is Focus. Check the following tutorial for details:
Focus on Swing - Java World
And check the following tip for a quick solution:
Setting the Initial Focused Component in a Window - Java Almanac - jug.ORG.ua Wiki
JRootPane rootPane = topLevelContainer.getRootPane();