import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class CalculatorMain extends JFrame implements ActionListener
{
  public CalculatorMain()
  {
    // just a dialog box with a text field. and ok button
    JFrame expressionFrame = new JFrame("Expression Evaluator");
    JTextField text = new JTextField("");
    JButton okButton = new JButton("OK");

    // add action listener
    okButton.addActionListener(this);

    // setup close operation on frame and the layouts
    expressionFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    expressionFrame.getContentPane().setLayout(new BorderLayout());
    expressionFrame.getContentPane().add(text, BorderLayout.NORTH);
    expressionFrame.getContentPane().add(okButton, BorderLayout.SOUTH);

    // show the GUI
    expressionFrame.pack();
    expressionFrame.show();
  }

  public void actionPerformed(ActionEvent e)
  {
    // evaluate the expression
    ExpressionParser.test(myCalc.text.blah!!!!);    // this is where it goes tits up
  }

  public static void main(String[] args)
  {
    CalculatorMain myCalc = new CalculatorMain();
  }
}



// -----------------------------------------------------------
// other class file:

public class ExpressionParser
{
  public static void test(String expression)
  {
      // put something in the textfield to show we have access to it
  }
}