From the JavaDocs
public void setEnabled(boolean enabled)
Sets whether or not this component is enabled. A component that is enabled may respond
to user input, while a component that is not enabled cannot respond to user input.
Some components may alter their visual representation when they are disabled in order
to provide feedback to the user that they cannot take input.
For more info
http://docs.oracle.com/javase/7/docs/api/javax/swing/JComponent.html#setEnabled%28boolean%29
INFO : JButton extends AbstractButton which extends JComponent