Thread: Java Swing:

 
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
 
import javax.swing.*;
import javax.swing.border.Border;
 
public class TempConvertor extends JFrame implements ActionListener
{
	JButton Convert;
	JButton Reset;
	JTextField Cel;
	JTextField Fah;
	JLabel CelLbl;
	JLabel farenheight;
 
	TempConvertor()
	{
		JFrame j = new JFrame("Temp Convertor");
		j.setSize(200,175);
		j.setResizable(false);
		j.setLayout(new FlowLayout());
		j.setDefaultCloseOperation(EXIT_ON_CLOSE);
 
		//create buttons
		Convert = new JButton("Convert");
		Reset = new JButton("Reset");
 
		Convert.addActionListener(this);
		Reset.addActionListener(this);
 
		//create labels
		CelLbl = new JLabel("Celsius");
		farenheight = new JLabel("Farenheight");
 
		CelLbl.setVerticalAlignment(SwingConstants.BOTTOM);
		farenheight.setVerticalAlignment(SwingConstants.BOTTOM);
		Border border = BorderFactory.createEtchedBorder();
		CelLbl.setBorder(border);
		farenheight.setBorder(border);
 
		JPanel cp = ((JPanel) j.getContentPane());
		cp.setBorder(BorderFactory.createEmptyBorder(4,4,4,4));
 
		//create text fields
		Cel = new JTextField(5);
		Fah = new JTextField(5);
 
		Cel.setActionCommand("Cel");
		Fah.setActionCommand("Fah");
 
		//add TextFields
		j.add(CelLbl);
		j.add(Cel);
		j.add(farenheight);//label
 
		j.add(Fah);
 
		//add Buttons
		j.add(Convert);
		j.add(Reset);
 
		j.setVisible(true);	
	}
 
	public void actionPerformed(ActionEvent ae)
	{
		if(ae.getActionCommand().equals("Convert"))
		{
			if(Cel != null)
			{
			//convert to Cel
			int jml = Integer.parseInt(Cel.getText());
			int result = jml * 9/5 + 32;
			Fah.setText(Integer.toString(result));
			}
			else if(Fah != null)
			{
				//convert to Fah
				int jml = Integer.parseInt(Fah.getText());
				int result = (jml - 32) * 5/9;
				Cel.setText(Integer.toString(result));
			}
		}
		else
		{
			Cel.setText("");
			Fah.setText("");
		}
	}
 
 
	public static void main(String[] args)
	{
		new TempConvertor();
	}
}

I am learning java swing and I am having an issue on line 78. I want to convert Celsius to Fahrenheit which works. However when I try to convert F to C I get the following errors:

at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)

I thought my if statement would handle this for me but only my Cel JTextField seems to be working. Any Advice?

You have some minor confusion about what Cel and Fah are. First, since neither is a class name, their names should begin with lowercase letters as in cel and fah. The same is true of most (all?) of your other variable names.

Even without the name correction, Cel and Fah are objects, instances of JTextField and will never be null once they are properly initialized. Your if conditions checking if they are not null will always return true. What I believe you mean to do is to check if the text assigned to or in the JTextFields Cel and Fah is empty, something like:

if( !Cel.getText().equals( "" ) )

There are other logic issues to clean up after you've made those changes, but this should get you on the way.

Yes that is what I want trying to do. Thank you very much.