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Thread: JButton Auto-changing Reference Variable

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    Default JButton Auto-changing Reference Variable

    I want the reference variable for a JButton (say... b1) to automatically change with each iteration of a for loop. So:
    [CODE]
    for(int i=0;i<12;i++) {
      JButton b1 = mainButtonList.get(b1);
      //Code to edit each button specifically... (if statements)
      mainButtonList.set(i,b1);
      b1 = null;
    [/CODE]

    As you can see, there is only one reference variable right now so I'm not sure how I can really have any action listener figure out which button was pressed.

    getSource will return the reference variable. If they all are the same, how can you differentiate?

    What I am looking for is to change the reference used with each iteration. So maybe add some sort of b(i) statement so that the number next to be changes each time. But, I'm not sure if that would work since Java takes b(i) as the full reference variable if I'm not mistaken.

    Is this possible? If not, do you have any other suggestion?

    Thanks for your time!


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    Super Moderator Norm's Avatar
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    Default Re: JButton Auto-changing Reference Variable

    The value of b1 could be changed every time the assignment statement is executed:
    JButton b1 = mainButtonList.get(b1);
    depending on what the get() method returns.
    For each new value (a reference to a JButton) you can then use that reference to add a listener for the specific button that b1 points to at that time. The button objects referred to by b1 will have their contents changed to reflect the added listener. Then setting b1 to refer to a different button object will NOT change the contents of the button object that b1 pointed to before.

    how I can really have any action listener figure out which button was pressed.
    When an action event is created by a component (eg a JButton) the source field in the event object has a reference to the component that created the event(button pressed). The action listener can use getSource() to get that reference to that component.

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    Default Re: JButton Auto-changing Reference Variable

    Quote Originally Posted by Norm View Post
    When an action event is created by a component (eg a JButton) the source field in the event object has a reference to the component that created the event(button pressed). The action listener can use getSource() to get that reference to that component.
    But the problem there is that if the reference for b1 keeps getting changed, it's value is set to the last assignment before the button gets pressed. So if any of the other buttons are pressed, they will return exceptions because their references are null.

    Do I need to use a button group? I'm having trouble understanding how to use it from the API.

    EDIT: Scratch the button group. They can't be used with JButtons.
    Last edited by bgroenks96; June 19th, 2011 at 01:38 PM.

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    Super Moderator Norm's Avatar
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    Default Re: JButton Auto-changing Reference Variable

    The button objects that were pointed to by b1 (each in turn) still exist. Changing the value of b1 does NOT change the existence of the object that it pointed to. If the buttons are added to a GUI, then the GUI has references to the buttons, no matter what value is in b1. b1 is a temporary reference that can be set to null when the code is done adding the buttons to the GUI and adding listeners to the button.
    When the button is pressed, the button's object has a reference to the listener and will call its method passing a reference to itself in the event object. getSource() will get that reference.

    Write some code and test it. Then you'll know. Either it works or not. If not come back and post the errors.

  5. The Following User Says Thank You to Norm For This Useful Post:

    bgroenks96 (June 19th, 2011)

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    Default Re: JButton Auto-changing Reference Variable

    Quote Originally Posted by Norm View Post
    The button objects that were pointed to by b1 (each in turn) still exist. Changing the value of b1 does NOT change the existence of the object that it pointed to. If the buttons are added to a GUI, then the GUI has references to the buttons, no matter what value is in b1. b1 is a temporary reference that can be set to null when the code is done adding the buttons to the GUI and adding listeners to the button.
    When the button is pressed, the button's object has a reference to the listener and will call its method passing a reference to itself in the event object. getSource() will get that reference.

    Write some code and test it. Then you'll know. Either it works or not. If not come back and post the errors.
    You were right. Thanks for your help.

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    Default Re: JButton Auto-changing Reference Variable

    Many times its faster to write some test code and see what happens.

    But you should always read the API doc so you know what the choices are.

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    Default Re: JButton Auto-changing Reference Variable

    Quote Originally Posted by Norm View Post
    Many times its faster to write some test code and see what happens.

    But you should always read the API doc so you know what the choices are.
    Yeah the API is my second Bible. I could read it all day...

    I just thought that by reassigning the same reference variable you leave the previously assigned object with a reference of null.

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