ICS 201 – Introduction to Computer Science
Fall Semester 061
Programming Assignment # 4
All Sections
Due on Sunday Jan 07, 2007
Objectives
· Build a simple GUI application and learn key concepts in GUI.
· Become familiar with Java Swing.
Write a program to implement a simple calculator with a graphical user interface and the capabilities described below. The user interface should look like this:
In your implementation consider the following:
1. Try to use Java Exceptions when appropriate. For example, if you need to convert a string into an integer, write code that assumes the string represents a valid integer in a try clause and handle the exceptional case in a catch clause. A proper use of Exceptions usually yields a more manageable code.
2. To keep it simple, our calculator handles only integers so we don't really need the dot button (".").
3. The calculator will have several states. For example, in the beginning it expects a number (and not an operator), but after one digit has been inserted it expects either a number or an operator; You will need to enable/disable the appropriate buttons according to the calculator's state.
4. Use the JFrame class static method: setDefaultLookAndFeelDecorated to created JFrames with their Window decorations (such as borders, widgets to close the window, title...) provided by the current look and feel (true).
[JFrame.setDefaultLookAndFeelDecorated(true);]
/**
* Swing application to implement a simple calculator.
*/
import java.awt.*;
import java.awt.event.*;
import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import javax.swing.*;
import javax.swing.border.EtchedBorder;
/**
* class Calculator: implements a simple calculator in Swing.
*
*/
public class Calculator implements ActionListener {
private JFrame frame;
private JPanel mainPanel;
private JPanel buttonsPanel;
private JLabel display;
Set digitKeySet = new HashSet();
Set operatorKeySet = new HashSet();
JButton equalButton;
// variables to keep state
private StringBuffer registerA = new StringBuffer();
private StringBuffer registerB = new StringBuffer();
private char operator;
private boolean firstNumberAlreadyInput = false;
/**
* Constructor: builds up the frame, panels, buttons and text-field.
*/
public Calculator() {
// Create and set up the window.
frame = new JFrame("Calculator");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Create and set up the panel.
mainPanel = new JPanel(new BorderLayout());
buttonsPanel = new JPanel(new GridLayout(4, 4));
/*
* create the buttons (by 'addButtonToPanel') and add each
* one to the right botton set.
* we create the buttons in the right order so they appear
* in the right way on the GUI.
*/
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "7"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "8"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "9"));
operatorKeySet.add(addButtonToPanel(buttonsPanel, this, "/"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "4"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "5"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "6"));
operatorKeySet.add(addButtonToPanel(buttonsPanel, this, "*"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "1"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "2"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "3"));
operatorKeySet.add(addButtonToPanel(buttonsPanel, this, "-"));
digitKeySet.add(addButtonToPanel(buttonsPanel, this, "0"));
JButton dot = addButtonToPanel(buttonsPanel, this, ".");
equalButton = addButtonToPanel(buttonsPanel, this, "=");
operatorKeySet.add(addButtonToPanel(buttonsPanel, this, "+"));
// displaye "." button
dot.setEnabled(false);
setButtonsEnabled(operatorKeySet, false);
equalButton.setEnabled(false);
// Add the display field
display = new JLabel("0");
display.setBackground(Color.WHITE);
display
.setBorder(BorderFactory
.createEtchedBorder(EtchedBorder.RAISED));
// Add to main panel
mainPanel.setBorder(BorderFactory.createEmptyBorder(1, 1, 1, 1));
mainPanel.add(display, "North");
mainPanel.add(buttonsPanel, "Center");
// Add the panel to the window.
frame.getContentPane().add(mainPanel, BorderLayout.CENTER);
// Display the window.
frame.setSize(new Dimension(220, 240));
frame.setVisible(true);
}
/*
* (non-Javadoc)
*
* @see java.awt.event.ActionListener#actionPerformed(java.awt.event.ActionEvent)
*
* This function will be called every time a button is pressed (this is a
* GUI event we registered on).
* We can expect either a digit, an operator or '='. We record
* the state using the variables: 'registerA',
* 'registerB', 'operator' and 'firstNumberAlreadyInput'
*/
public void actionPerformed(ActionEvent event) {
Object source = event.getSource();
if (source != null) {
String input = ((JButton) source).getText();
if (digitKeySet.contains(source)) {
if (firstNumberAlreadyInput) {
registerB.append(input);
display.setText(registerB.toString());
equalButton.setEnabled(true);
} else {
registerA.append(input);
display.setText(registerA.toString());
setButtonsEnabled(digitKeySet, true);
setButtonsEnabled(operatorKeySet, true);
equalButton.setEnabled(false);
}
} else if (operatorKeySet.contains(source)) {
operator = input.charAt(0);
firstNumberAlreadyInput = true;
setButtonsEnabled(digitKeySet, true);
setButtonsEnabled(operatorKeySet, false);
equalButton.setEnabled(false);
} else {
display.setText(doCalculation(registerA.toString(), registerB
.toString(), operator));
registerA.setLength(0);
registerB.setLength(0);
firstNumberAlreadyInput = false;
setButtonsEnabled(digitKeySet, true);
setButtonsEnabled(operatorKeySet, false);
equalButton.setEnabled(false);
}
}
}
/*------*\
Static Methods (utility functions)
\*------*/
/**
* uses 'registerA', 'registerB' and 'operator' to convert into integers and
* compute the result.
*
* @param rand1
* @param rand2
* @param op
* @return
*/
private static String doCalculation(String rand1, String rand2, char op) {
final char beep = '\u0007';
try {
int numA = new Integer(rand1.toString()).intValue();
int numB = new Integer(rand2.toString()).intValue();
switch (op) {
case '+':
return String.valueOf(numA + numB);
case '-':
return String.valueOf(numA - numB);
case '*':
return String.valueOf(numA * numB);
default:
return String.valueOf(numA / numB);
}
} catch (ArithmeticException error) {
System.out.print(beep);
return " E R R O R";
}
}
/**
* Add the button to panel. Have 'text' as the button's text and name. Add
* listener to button's events.
*
* @param panel
* @param listener
* @param text
* @return
*/
private static JButton addButtonToPanel(JPanel panel,
ActionListener listener, String text) {
JButton button = new JButton(text);
button.setName(text);
button.addActionListener(listener);
panel.add(button);
return button;
}
/**
* call setEnabled on all buttons in the Set.
*
* @param buttons
* @param enabled
*/
private static void setButtonsEnabled(Set buttons, boolean enabled) {
for (Iterator i = buttons.iterator(); i.hasNext();) {
JButton button = (JButton) i.next();
button.setEnabled(enabled);
}
}
/**
* Create the GUI and show it. For thread safety, this method should be
* invoked from the event-dispatching thread.
*/
private static void createAndShowGUI() {
// Make sure we have nice window decorations.
JFrame.setDefaultLookAndFeelDecorated(true);
Calculator calculator = new Calculator();
}
/**
* main function to run Calculator
*
* @param args
*/
public static void main(String[] args) {
// Schedule a job for the event-dispatching thread:
// creating and showing this application's GUI.
javax.swing.SwingUtilities.invokeLater(new Runnable() {
public void run() {
createAndShowGUI();
}
});
}
}