Take a look at the inheritance hierarchy of the javax.swing.JFrame class in the standard runtime API documentation. This hierarchy indicates that JFrame is a Frame and Frame is a Window and Window is a Container and Container is a Component and finally Component is an Object (just like all the other classes are in Java since the Object class is the root class from which they all descend). A more general way to look at this is to say a child class can be used any place any of its ancestor classes can be used. This means that JFrame is a Frame and a Window and a Container and a Component and an Object.
If we take a look at the inheritance hierarchy of the javax.swing.JFrame class, it says that a JFrame is a Frame, a Frame is a Window, a Window is a Container, a Container is a Component, and a Component is an Object. By applying the definition of inheritance given at the top, we can say that:
A JFrame is a frame, window, container, component, and an object all in one. We can compare inheritance to this:
We make our own Jframe, called MyJFrame
public class MyJFrame extends JFrame
{
MyJFrame (String title){� title, size�
addWindowListener(new WindowCloser());
setDefaultCloseOperation(DO_NOTHING_ON_CLOSE);
}
class WindowCloser extends WindowAdapter {
public void windowClosing (WindowEvenet event) {
int choice = JOptionPane.showConfirmDialog (MyJFrame.this,�Do you really want to quit:, �Confirm quit�,JOptionPane.YES_NO_OPTION);
if (choice == JOptionPane.YES_NO_OPTION)
System.exit(0); }
}
}
Result