UserInterface.java

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.JLabel;
import javax.swing.JButton;
import java.awt.GridLayout;
import java.awt.FlowLayout;
import java.awt.event.*;


public class UserInterface extends JFrame{

    /*
     * The main interface for the users. Yet it contains a textfield for
     * the input, a label for the output and two buttons. One button to
     * make calculation and one to exit the program. In the input field
     * pressing the enter also do calculate.
     * */

    private JPanel workingPanel = new JPanel( new GridLayout(2,1));
    private JPanel buttonPanel = new JPanel( new GridLayout(2,1));
    private JTextField inputField = new JTextField(20);
    private JLabel outputField = new JLabel("0");
    private JButton calcButton = new JButton("Calculate");
    private JButton exitButton = new JButton("Exit");

    public UserInterface(String title){
        super(title);
        workingPanel.add(inputField);
        workingPanel.add(outputField);
        inputField.addKeyListener(new KeyListener(){
            public void keyPressed(KeyEvent e){
                if(e.getKeyCode() == KeyEvent.VK_ENTER){ // Only the
                    //enter have some special meaning...
                    doCalculate(inputField.getText());
                }
            }
            public void keyReleased(KeyEvent e){

            }
            public void keyTyped(KeyEvent e){

            }
        });
        workingPanel.setVisible(true);
        buttonPanel.add(calcButton);
        calcButton.addMouseListener(new MouseListener(){
            public void mouseClicked(MouseEvent e){

            }
            public void mouseEntered(MouseEvent e){

            }
            public void mouseExited(MouseEvent e){

            }
            public void mousePressed(MouseEvent e){
                doCalculate(inputField.getText());//It's enough to press
                //the button.
            }
            public void mouseReleased(MouseEvent e){

            }
        });
        exitButton.addMouseListener(new MouseListener(){
            public void mouseClicked(MouseEvent e){
                dispose(); // Just to let the user change his mind.

            }
            public void mouseEntered(MouseEvent e){

            }
            public void mouseExited(MouseEvent e){

            }
            public void mousePressed(MouseEvent e){

            }
            public void mouseReleased(MouseEvent e){

            }
        });
        buttonPanel.add(exitButton);
        buttonPanel.setVisible(true);
        super.setLayout(new FlowLayout());
        super.add(workingPanel);
        super.add(buttonPanel);
        super.setDefaultCloseOperation(EXIT_ON_CLOSE);
        super.pack();
        super.setResizable(false);
        super.setVisible(true);
    }

    private void doCalculate(String forward){
        try{
            outputField.setText( Calculator.getResult( forward ).toString() );
        } catch(BraNotEnough brn){
            outputField.setText(brn.getMessage());
        } catch(OperandsNotEnough one){
            outputField.setText(one.getMessage());
        } catch(NumberFormatException nan){
            outputField.setText("Something is wrong..");
        }
    }

}