Thread: 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;
}

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

Originally Posted by Norm

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.