An Adapter is simply a concrete class which implements all the methods of a Listener interface as empty functions. They are convenience classes made because of the tendency to implement Listeners as anonymous classes.
For example, let's say we want to add a Listener to a JFrame to detect a mouse click:
// implementing a Listener
JFrame frame = new JFrame();
frame.addMouseListener(new MouseListener() {
void mouseClicked(MouseEvent e) {
// do something here
}
void mouseEntered(MouseEvent e) {
}
void mouseExited(MouseEvent e) {
}
void mousePressed(MouseEvent e) {
}
void mouseReleased(MouseEvent e) {
}
});
Note how this has a lot of extra code that does nothing.
// implementing an Adapter
JFrame frame = new JFrame();
frame.addMouseListener(new MouseAdapter() {
void mouseClicked(MouseEvent e) {
// do something here
}
});
Note now how we only need to implement one method. This is much cleaner and easier to read.
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