Java动作侦听器和JButton

Question

I have a gui class which has three different JButtons linked to one ActionListener .

In the ActionListener class I want an interaction between these three JButtons in a way that allows the program to "remember" which button was clicked previously.

For example:

1. If button1 is clicked --> remember this,
2. Then when button2 gets clicked next: do a action relative to button1 being clicked.

In other words if button1 click, now inside the if clause check for button2 click.

Right now getActionCommand() does not allow me to use nested if statements because it only checks the current button clicked and has no "memory".

public void actionPerformed(ActionEvent e){
  if (Integer.parseInt(e.getActionCommand()) == 0){
    System.out.println("This is Jug 0");
    // wont be able to print the following
    if (Integer.parseInt(e.getActionCommand()) == 1){
      System.out.println("This is Jug 1 AFTER jug 0"); //I will never be able to print this
    }
  }
}

Answer 1

From my understanding of what you are looking todo...

So one way of achieving this is to create a instance variable that is a Boolean, so will be set true is the button has been previously clicked and then you could check inside your method if that flag has been set true. Drawback of that approach would be that the flag will always be true once it has been clicked once. You'll have to implement a way to reset this flag.

private boolean hasButtonOneBeenPressed = false; //set this to true when the button has been clicked

public void actionPerformed(ActionEvent e){
  if (Integer.parseInt(e.getActionCommand()) == 0 && !hasButtonOneBeenPressed){
    System.out.println("This is Jug 0");
    // wont be able to print the following
  } else if(Integer.parseInt(e.getActionCommand()) == 1 && hasButtonOneBeenPressed){
      System.out.println("This is Jug 1 AFTER jug 0");
    } else {
      //do something else
   }
}

Answer 2

You've given the ActionListener behavior -- it has an actionPerformed method, but you've yet to give it state -- fields that allow it to remember where it is and what it's done. A boolean field or two is likely all you need here. Either that or a JButton field where you place the last button pressed -- all depending on what you want to do with this information.

For instance, if you were coding a memory game, then you could have a JButton field that holds the last button pressed. If the field is null on actionPerformed, you know that the user is pressing the first button, and so you assign it to the field. If the field holds a button when actionPerformed is pressed, then you know the 2nd button is pressed. If it's not the same as the first, you compare image icons and behave accordingly, and then set the JButton field to null.

Answer 3

I just assume that u want just the last button pressed, so you just need a variable to store your last button. In case u want the full button pressed history, just use an array where you add your pressed buttons.

PS: This uses java 8 lambdas for the ActionListeners.

private void initComponents() {
    JButton b1 = new JButton();
    JButton b2 = new JButton();
    JButton b3 = new JButton();
    b1.addActionListener((e)-> onButton1Pressed());
    b2.addActionListener((e)-> onButton2Pressed());
    b3.addActionListener((e)-> onButton3Pressed());
}

int lastButton = -1;
private void onButton1Pressed() {
    switch (lastButton) {
        case 1:
            break;
        case 2:
            break;
        case 3:
            break;
        default:
            break;
    }
    lastButton = 1;
}    

private void onButton2Pressed() {
    switch (lastButton) {
        case 1:
            break;
        case 2:
            break;
        case 3:
            break;
        default:
            break;
    }
    lastButton = 2;
}