Develop Reference

Member Object Calling Class Method

I hope this question is not really a repetition of an existing one! I searched and found no good answer to my question. Here it is:
I have a class MyGame that contains a Button member object. Whenever that button is clicked, MyGame should do something.
class MyGame extends Application {
MyBoard board = new MyBoard();
MyButton btn = new MyButton();
public MyGame() {
board.add(btn);
}
// this method should be called whenever the button is clicked!
public void doSomething() {
doingSomething();
}
}
class MyButton extends Button {
int someData;
// some code here
public MyButton() {
this.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent arg0) {
MyGame.doSomething(); // ==> NOT POSSIBLE!!!
}
});
}
}
Would an interface be the best way to make the communication between the MyButton and MyGame go? If so, how would you do it?
I don't want to hand over a reference of MyGame object to the MyButton object! I think this is not a good way to resolve this problem.
I appreciate any suggestions and help!
Cheers

In the constructor of MyGame you can add an ActionListener to btn that will be called when an action is performed on the button.
btn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
// Insert thing to do within MyGame here
}
});

One way is to do it the other way around (game should be a member of button). I know that you think "it is not a good way to resolve this problem", but you think wrong, there is really nothing wrong with it.
Alternatively, move the registering of the listener out of the button's constructor into the game itself:
public MyGame() {
btn.setOnAction(new EventHandler<ActionEvent>() {
public void handle(ActionEvent arg0) { doSomething(); }
});
}

Make the "button action" an interface that can be passed to the constructor when creating MyButton. Example:
public MyButton(final Runnable action) {
this.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent arg0) {
action.run(); // POSSIBLE!!!
}
});
}
or save the action in a MyButton instance field:
public MyButton(Runnable action) {
buttonAction = action; // make buttonAction an instance field
this.setOnAction(new EventHandler<ActionEvent>() {
#Override
public void handle(ActionEvent arg0) {
buttonAction.run();
}
});
}
Then when MyGame creates a new MyButton, the MyGame gets to tell the button what to do when the button is clicked:
MyButton btn = new MyButton(new Runnable() {
#Override
public void run() {
MyGame.this.doSomething();
}
}
or in Java 8:
MyButton btn = new MyButton(this::doSomething);
NOTE: I haven't yet tested this. I think I got the syntax right, but I may have made a mistake. You may need to assign btn in the MyGame constructor rather than in an initializer expression.
This is a generalized approach (dependency injection?) that works in lots of situations. There may be other solutions specific to Button (or other Swing components for which a listener mechanism is already defined). But this mechanism reduces coupling, because the MyButton doesn't really need to know anything about who created it, and the MyGame doesn't need to know what the MyButton plans to do with the Runnable action. Some other possible solutions involve having MyGame doing some of MyButton's work, which increases coupling.

Calling actionlistener of a disabled JButton

I was working on something in which I need to call the actionlistner of a disabled jbutton from another function. How it can be done?

Make a new method which will be called by the disabled jbutton, write all the code there which will be executed when you click the button. You can not call the actionlistiner in other way.
...
JButton disButton = new JButton("Disabled");
disButton.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
//do not write any statement here
doSomething();
}
});
...
private void doSomething() {
//all action event execution code here
System.out.println("I am in the action listener");
}
....
//in the other method or another button click event call doSomething()
//even button is disables like
JButton Button = new JButton("Submit");
Button.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent arg0) {
doSomething();
}
});
//or from another method
public void method() {
doSomething();
}

You cannot call/do actions on disabled GUI controls.That is what actually disable means
What you can do is create a separate common method like doClick() and call where ever you need.

Changing a variable in another class without a static variable?

in the program that I am writing at the moment, I have 2 JFrames (each in a different class, each has a different purpose, however you could consider the widget frame to be a slave of some sort), one is a main window, and the other is a 'widget' that pops up upon hitting a button in the main window.
I only want one copy of the widget open at one time. I am currently doing this through boolean variables under an actionPerformed action listener. Below is the action listener for the main window.
public void actionPerformed(ActionEvent e) {
if(getOpenWidget() == false){
System.out.println(getOpenWidget()); //test line
widget.initialize(); // please note that the instance "widget" is declared just after "public class MainWindow{" :)
widget.frame.setVisible(true);
setOpenWidget(true);
System.out.println(getOpenWidget() ); // test line
}else{
System.out.println(getOpenWidget());
JOptionPane.showMessageDialog(frame, "There is already an instance of the Booking Widget open.");
}
}
Now the booking widget is open, on the booking widget there is a cancel button. Below here is the action listener for the widget's 'cancel' button.
btnCancel.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
MainWindow ui = new MainWindow();
frame.dispose();
ui.setOpenWidget(false);
}
}
Now, upon hitting my button in the main window again, in theory, the openWidget bool should be false, and allow me to open another window, however in the cancel button action listener, my variable isnt changed. So, am I going about my problem in the right way without making openWidget a static variable?(I should be using getters and setters right?)
What am I doing wrong and what don't I understand about instantiating a new instance of the main window every time I click that button?
Also, my getters and setters are stock standard as follows.
void setOpenWidget(boolean val){
this.openWidget = val;
}
boolean getOpenWidget(){
return this.openWidget;
}

Just pass the reference of MainWindow to the Widget class so that it can update its flag on cancel button.

You are calling setOpenWidget(false) on some other new instance you have created using this line MainWindow ui = new MainWindow();
You should call setOpenWidget(false) using same instance from which you have initialised widget. Pass the reference of MainWindow to widget while creating widget and invoke setOpenWidget(false) using that reference

When you are creating the object of widget within MainWindow you can call it like this:
widget = new Widget(this);
And change the Widget Window Constructor as follows:
MainWindow ui;
public Widget(MainWindow mw)
{
this.ui = mw;
//...initialize btnCancel...
btnCancel.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent arg0) {
frame.dispose();
ui.setOpenWidget(false);
}
});
//..do all other stuffs here...
}

Simple memory game with replay button

I want to build a simple memory game. I want to put a replay button, which is play again the memory game.
I have built a class named MemoryGame and a main class.
Here is the part of the ButtonListener code.
public void actionPerformed(ActionEvent e) {
if (exitButton == e.getSource()) {
System.exit(0);
}
else if (replayButton == e.getSource()) {
//How can I declare it?
}
}
If I declare the replay button as :
new MemoryGame();
It's work fine, but it pops up another windows.
I want to clear the current display and return to the beginning, without a new windows. How can I do that?
EDIT :
I think I need to rewrite the code of my program, because my program does not have the init() method as suggested which is the initial state of the program.
My Java knowledge is very limited and usually I create less method and dump most into a method.
I will try to redo my program.
Thanks for the suggestions.

Show us what is inside the MemoryGame how you create its initial state. Effectively what folks are suggesting here is for you is to have an initial method which will set-up the game state which the MemeoryGame constructor will call. Then on replay-button of the game you call this method.
Something along these lines:
void init(){
this.x = 10;
this.y = 10;
}
public MemoryGame(){
init();
}
public void actionPerformed(ActionEvent e) {
if (exitButton == e.getSource()) {
System.exit(0);
}
else if (replayButton == e.getSource()) {
init();
}
}

one way you can do it although it might be dirty, is to grab your MemoryGame constructor, and put the stuff inside it inside another method, and call that method in your constructor and inside the button event.
as an example i have made the following class and it resets itself with the use of the previous technique:
public class App extends JFrame{
public static void main(String[] args){
new App();
}
public App(){
init();
}
private JButton changeColorButton;
private JButton resetAppButton;
private JPanel panel;
private void init() {
changeColorButton=null;
resetAppButton=null;
panel=null;
this.setSize(200,400);
this.setVisible(true);
this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
panel = new JPanel();
panel.setBackground(Color.white);
panel.setPreferredSize(new Dimension(200,400));
changeColorButton = new JButton("Change");
changeColorButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
panel.setBackground(Color.black);
panel.repaint();
}
});
changeColorButton.setPreferredSize(new Dimension(100,100));
resetAppButton = new JButton("Reset");
resetAppButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
init();
}
});
resetAppButton.setPreferredSize(new Dimension(100,100));
panel.add(changeColorButton);
panel.add(resetAppButton);
this.add(panel);
this.validate();
}
}
what this app does is it has two buttons. one changes the color and the other resets the app itself.

You should think about re-factoring your code so that the MemoryGame class does not create the GUI, then you wont be recreating it whenever you initialise a new Game.
It's a good idea to keep program logic separate to UI code.

What you could do is you could call dispose() on your JFrame. This will get rid of it and go to your title screen like this:
Here's the button code
public void actionPerformed(ActionEvent event)
{
if (closeButton = event.getSource())
{
System.exit(0);
}
if (playAgainButton = event.getSource())
{
Game.frame.dispose(); // Your class name, then the JFrame variable and call dispose
}
}
This will work but you may have a few problems reseting your program. If so then create a reset method where you can reset all your variables and call when playAgainButton is clicked. For example:
public void reset()
{
// Right here you'd reset all your variables
// Perhaps you have a gameOver variable to see if it's game over or not reset it
gameOver = false;
}

Programmatically Generating Actionevent in Java

I'm making an App. in java , in which there is a Button to which I have added an actionlistener. The ActionEvent it(the button) generates executes some code. Now I want this piece of code to run whenever the app. starts and without pressing the button. I mean, I want to generate the Actionevent (without pressing the button) so that the piece of code the ActionPerformed contains gets executed as the app. start. After that, it may run whenever I press the button.

You can create ActionEvents like any other Java Object by just using the constructor. And then you can send them directly to the component with Component.processEvent(..)
However, in this case I think you are better making your code into a separate function which is called both:
By the ActionListener when the button is pressed
Directly by your application startup code (possibility using SwingUtilities.invokeLater() or SwingUtilities.invokeAndWait() if you need it to happen on the event-handling thread)
This way you don't mix up presentation logic with the business logic of whatever the code does....

Yes it can be done, but it doesn't really make sense, since your goal isn't to press a button or to call an ActionListener's code, but rather to have a common behavior on button press and on program start up. To me the best way to achieve this is to have a method that is called by both the actionPerformed method of the ActionListener and by the class at start up.
Here's a simple example. In the code below, a method disables a button, turns the JPanel green, and starts a Timer that in 2 seconds enables the button and resets the JPanel's background color to its default. The method that causes this behavior is called both in the main class's constructor and in the JButton's ActionListener's actionPerformed method:
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
public class ActionOnStartUp extends JPanel {
private static final int PANEL_W = 400;
private static final int PANEL_H = 300;
private static final int TIMER_DELAY = 2000;
private JButton turnGreenBtn = new JButton("Turn Panel Green for 2 seconds");;
public ActionOnStartUp() {
turnPanelGreen();
turnGreenBtn.addActionListener(new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
turnPanelGreen();
}
});
add(turnGreenBtn);
}
public void turnPanelGreen() {
setBackground(Color.green);
turnGreenBtn.setEnabled(false);
new Timer(TIMER_DELAY, new ActionListener() {
public void actionPerformed(ActionEvent ae) {
setBackground(null);
turnGreenBtn.setEnabled(true);
((Timer) ae.getSource()).stop(); // stop the Timer
}
}).start();
}
#Override
public Dimension getPreferredSize() {
return new Dimension(PANEL_W, PANEL_H);
}
public static void createAndShowGui() {
JFrame frame = new JFrame("Foo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().add(new ActionOnStartUp());
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGui();
}
});
}
}

Usually, the button action event responds to an external event, to notify the application that the user (or rather something or someone) interacted with the application. If your button executes some code that you want to also execute at application start, why not just place everything at it's proper place?
Example:
public class SomeSharedObject {
public void executeSomeCode() { /*....*/ }
}
Set the button with something like
public void setButtonAction(final SOmeSharedObject obj) {
button.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
obj.executeSomeCode();
}
});
}
And run at application start with something like
public void initApplication(SomeSharedObject obj) {
obj.executeSomeCode();
}
And, if the code you need to execute takes a while to complete, you might want to use a separate thread inside your actionPerformed button event so your application UI does not freeze up.

Just Call JButton.doClick() it should fire the ActionEvent associated with the JButton.