Java Solutions: ActionListener

Showing posts with label ActionListener. Show all posts

Friday, December 22, 2017

Use MethodHandle to dynamically invoke method

MethodHandle is introduced in Java 7. For dynamic method invoking, it is faster than reflection.

In the code below, class MethodHandleTest2 has three JTextField fields and an objModified method. When any of the JTextField fields is modified, the objModified method will be called to handle the modification accordingly.

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.lang.invoke.MethodHandle;
import java.lang.invoke.MethodHandles;
import java.lang.invoke.MethodType;
import java.lang.reflect.InvocationTargetException;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class MethodHandleTest2 extends JFrame{
public MethodHandleTest2() {
JTextField[] data = {new JTextField("Peach", 20),
new JTextField("Papaya", 20),
new JTextField("Mango", 20)};
JPanel panel = new JPanel(new GridLayout(3, 1));

for (int i=0; i<data.length; i++){
try {
data[i].addActionListener(new ObjectActionListener("objModified",
new Object[]{this, data[i], "Field "+(i+1)+" Modified"}
));
panel.add(data[i]);
} catch (NoSuchMethodException e){
System.out.println(e.getMessage());
}
}
this.add(panel);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
this.setSize(700, 300);
this.pack();
}

public static void main(String[] args){
javax.swing.SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
(new MethodHandleTest2()).setVisible(true);
}
});
}

public class ObjectActionListener implements ActionListener {
private Object[] parameters = null;
private String methodName = null;

public ObjectActionListener(String methodName, Object[] parameters)
throws NoSuchMethodException, SecurityException {
this.methodName = methodName;
this.parameters = parameters;
}

private MethodHandle getMethod() throws NoSuchMethodException,
IllegalAccessException {

//For the objModified method, its return type is void, and it takes
// a JTextField argument and a String argument.
MethodType mt = MethodType.methodType(void.class, JTextField.class, String.class);

//Get the MethodHandle: argument1 is the class where the method is located;
// argument2 is the method name;
//argument3 is the method type of the method signature
MethodHandle mh = MethodHandles.lookup()
.findVirtual(MethodHandleTest2.class,
methodName,
mt);
return mh;
}

@Override
public void actionPerformed(ActionEvent event) {
try {
MethodHandle method = getMethod();
//The invoke method is supposed to be able to take an array argument.
//Somehow, it does not work for me in my test code.
//So, I have to put each component of the array in the arguments.
method.invoke(parameters[0], parameters[1], parameters[2]);
} catch (IllegalAccessException e) {
System.out.println(e.getMessage());
} catch (InvocationTargetException e) {
System.out.println(e.getMessage());
} catch (Throwable e) {
System.out.println(e.getMessage());
}
}
}

public void objModified(JTextField obj, String message){
String text = obj.getText();
System.out.println(message+": "+text);
}
}

The code using reflection to do the same job can be found here

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Thursday, December 14, 2017

Set up a Timer to repeatedly execute a piece of code or a task or to repeatedly update the state of your objects

Lets say, you have an integer field and you want to increment it by 5 every minute.

public class TimerTest {
private int theValue = 0;
private javax.swing.Timer timer1 = null;

public TimerTest() {
//Set up the timer to perform the action repeatedly
//after a delay of 1 minute which is 60000 milliseconds.
timer1 = new javax.swing.Timer(60000, new TimerAction());
timer1.start();

}

private class TimerAction implements ActionListener {
@Override
public void actionPerformed(ActionEvent e) {
theValue += 5;
System.out.println("The value currently is "+theValue);
}
}
}

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Wednesday, November 30, 2016

Create a popup menu

In the case you want to display a set of options once you have clicked a component, you may use a popup menu to show the options.

Lets say you have a JButton, when it is clicked, a menu will popup.

JButton popMenuButton = new JButton("Your Choices');
popMenuButton.addActionListener(new PopupListener());

JPopupMenu popMenu = new JPopupMenu();
JMenuItem choice1 = new JMenuItem();
JMenuItem choice2 = new JMenuItem();

private class PopupListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
buildPopupMenu();
}
}

private void buildPopupMenu() {
popMenu.setLabel("Options");

choice1.setText("Choice 1");
choice1.setActionCommand("Choice 1");
choice1.setMnemonic(1);
choice1.addActionListener(new ChoiceListener());
popMenu.add(choice1);

choice2.setText("Choice 2");
choice2.setActionCommand("Choice 2");
choice2.setMnemonic(2);
choice2.addActionListener(new ChoiceListener());
popMenu.add(choice2);

popMenu.setRequestFocusEnabled(true);
popMenu.setBorderPainted(true);
popMenu.show(popMenuButton, 5, -60);
}

private class ChoiceListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
popMenu.setVisible(false);
Object obj = e.getSource();
if (obj == choice1) {
//Display result of choice 1
} else if (obj == choice2) {
//Display result of choice 2
}
}
}

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