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Thread: Calculator help

  1. #1
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    Default Calculator help

    I am making a simple program the user enters in a number using JButtons 0-9 and then the user clicks gallons or miles to add the number to one or the other. Here is my code:

    import java.awt.GridLayout;
    import java.awt.event.ActionEvent;
    import java.awt.event.ActionListener;
    import javax.swing.*;
     
     
    public class SouthPanel extends JPanel{
    	JLabel milesTitle, fuelTitle, saveTitle, milesText, fuelText, saveText, topLabel;
    	JButton miles, gallons, save;
     
    	public SouthPanel (JLabel northLabel){
    		topLabel = northLabel;
    		milesTitle = new JLabel("total miles");
    		fuelTitle = new JLabel("fuel consumed");
    		saveTitle = new JLabel("save to file");
     
    		milesText = new JLabel("0.0");
    		fuelText = new JLabel("0.0");
    		saveText = new JLabel("\"statistics.txt\"");
     
    		JButton miles = new JButton("miles");
    		JButton gallons = new JButton("gallons");
    		JButton save = new JButton("Save");
     
    		ButtonListener listener = new ButtonListener();
    		miles.addActionListener(listener);
    		gallons.addActionListener(listener);
    		save.addActionListener(listener);
     
    		setLayout(new GridLayout(3,3));
     
    		add(milesTitle);
    		add(milesText);
    		add(miles);
    		add(fuelTitle);
    		add(fuelText);
    		add(gallons);
    		add(saveTitle);
    		add(saveText);
    		add(save);
    	}
    	private class ButtonListener implements ActionListener{
     
    		public void actionPerformed (ActionEvent event){
    			double temp = 0;
    			double temp2 = 0;
    			double sumit = 0;
     
    			if (event.getSource() == miles){
    				temp = Double.parseDouble(topLabel.getText());
    			    temp2 = Double.parseDouble(milesText.getText());
    				sumit = temp + temp2;
    			    milesText.setText("" + sumit);
    			    topLabel.setText("");
    			}
     
    			if (event.getSource() == gallons){
    				temp = Double.parseDouble(topLabel.getText());
    			    temp2 = Double.parseDouble(fuelText.getText());
    				sumit = temp + temp2;
    			    fuelText.setText("" +sumit);
    			    topLabel.setText("");
    			}
     
    	   }
       }
    }

    It runs and compiles fine, but my two button listeners dont seem to be working. When i click one of them nothing happens. Is there something wrong with-in the code of each button?


  2. #2
    Administrator copeg's Avatar
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    Default Re: Calculator help

    The references to the buttons the ActionListener checks for are never initialized - the constructor creates JButtons which are added to the GUI, but these are out of scope after the constructor is called. Change it so the variables are initialized and used:

    miles = new JButton("miles");//as opposed to JButton miles = new JButton("miles");

  3. The Following User Says Thank You to copeg For This Useful Post:

    Bradshjo (November 1st, 2010)

  4. #3
    Junior Member
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    Default Re: Calculator help

    thanks a lot it worked...stupid error that costed me hours. But thats programming sometimes.

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