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:

Code Java:

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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("");
			}
 
	   }
   }
}

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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?

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:

Code :

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

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