Here I would like to demonstrate a simple use of JMenuItems being used with Single Listener for the entire system.
A simple sample of use would probably be SingleInstance Desktop Application.
Lets see how that is done here.
- First lets create a OneListener class that should be able to listen to ActionEvents and also be able to add Commands to itself. Please refer to my previous post on Command,Singleton if you would like to see more about this patterns and there usage.
package com.shaafshah.jmenus;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import javax.swing.AbstractButton;
// Implements the ActionListener and is a Singleton also.
public class OneListener implements ActionListener{
private static OneListener oneListener = null;
// Holds the list of all commands registered to this listener
private ArrayList<Command> commandList = null;
// A private constructor
private OneListener(){
commandList = new ArrayList<Command>();
}
// Ensuring one instance.
public static OneListener getInstance(){
if(oneListener != null)
return oneListener;
else return oneListener = new OneListener();
}
// Add the command and add myself as the listener
public void addCommand(Command command){
commandList.add(command);
((AbstractButton)command).addActionListener(this);
}
// All Events hit here.
@Override
public void actionPerformed(ActionEvent e) {
((Command)e.getSource()).execute();
}
}
In the above code, the addCommand method adds the command Object and adds a listener to it.
Now how is that possible.
Basically because I am categorizing my UI objects as Commands with in the system having some UI. And I am also assuming that these commands are Currently AbstractButton i.e. JMenuItem, JButton. Lets have a look at the Command Interface and its Implementation.
