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Thread: Can someone help me out

  1. #1
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    Default Can someone help me out

    hey, I am fairly new to Java and I have to write a program that uses the mvc design pattern. It calculates the maximum data rate when the user changes the signal to noise and bandwidth. I need to create an action listener for when the user changes the values but I am not sure how to do that.

    private JPanel createBandwidthPanel(){
    	JPanel bandwidthPanel = new JPanel();
    	bandwidthPanel.setLayout(new BoxLayout(bandwidthPanel, BoxLayout.LINE_AXIS));
    	JLabel bandwidthLBL = new JLabel("Bandwidth(in hertz):");
    	JTextField bandwidthTXTFLD = new JTextField();
     
    	bandwidthTXTFLD.addActionListener(new ActionListener(){
     
     
    	public void actionPerformed(ActionEvent e) {
    		Double.parseDouble(bandwidthTXTFLD.getText());
     
     
    	}
    	});
     
    	bandwidthPanel.add(bandwidthLBL);
    	bandwidthPanel.add(bandwidthTXTFLD);
     
    	return bandwidthPanel;
    }

  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Can someone help me out

    You've already written an ActionListener. I'm not sure what your question is? I'd start by adding a print statement in there at least.
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  3. #3
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    Default Re: Can someone help me out

    it's complaining that the txtfield should be final and I don't think it's supposed to be.

  4. #4
    Super Moderator Norm's Avatar
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    Default Re: Can someone help me out

    variables defined/declared inside of a method go away when the method exits. Use of final tells the jvm to keep their value around so code like in a listener can access them.
    Or move their definition out of the method and it should work.
    If you don't understand my answer, don't ignore it, ask a question.

  5. #5
    Super Moderator curmudgeon's Avatar
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    Default Re: Can someone help me out

    Quote Originally Posted by Norm View Post
    variables defined/declared inside of a method go away when the method exits. Use of final tells the jvm to keep their value around so code like in a listener can access them.
    Or move their definition out of the method and it should work.
    Actually, I believe that it's because an inner class will make copies of the local variables that they use, and if the variable is not final, there's a chance that one version will change and not match the other.