import java.awt.*; import java.awt.event.*; import javax.swing.*; /** A Java program using a GUI to simulate a simple calculator with 4 arithmetic operations (+,-,*,/), negate (+/-), and a few other keys for clear, backspace, and recall; the program maintains one memory buffer for a previously entered number, it performs an operation as soon as two operands are entered; exceptions of bad number format are caught (Nov. 27, 2001) */ public class SimpleCalculator extends JFrame { /* the display field and buffers */ private JTextField displayField; private StringBuffer displayBuffer, numBuffer; private char opBuffer; /* calculator buttons and their labels */ private JButton[] keys; private String[] keyLabels; /** the constructor which creates the GUI with the buttons, set the size of the GUI and make it visible */ public SimpleCalculator() { super("A Simple Calculator"); // give title // initialize StringBuffers to the empty string "" displayBuffer = new StringBuffer(""); numBuffer = new StringBuffer(""); opBuffer = ' '; // blank character // create JButtons with texts and register event handler createButtons(); // add buttons to a JPanel with GridLayout JPanel panel = addButtons(); // create the GUI with a display field and the buttons Container container = getContentPane(); container.setLayout(new BorderLayout()); displayField = new JTextField(); displayField.setEditable(false); container.add(displayField, BorderLayout.NORTH); container.add(panel, BorderLayout.CENTER); setSize(290, 220); setVisible(true); } /** create a SimpleCalculator instance */ public static void main(String[] args) { SimpleCalculator app = new SimpleCalculator(); app.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); } /** create JButtons with texts, and register an event handler with the buttons */ private void createButtons() { // initilaize an array of Strings for button labels keyLabels = new String[] { "0", "1", "2", "+", "RC", "3", "4", "5", "-", "BP", "6", "7", "8", "*", "CL", "9", "+/-", ".", "/", "=" }; keys = new JButton[20]; // create 20 JButton references // create JButtons with the sepcified String labels for (int i = 0; i < 20; i++) keys[i] = new JButton(keyLabels[i]); // increase font size for operators, +/-, and = Font ft = new Font("Dialog", Font.PLAIN, 17); keys[3].setFont(ft); keys[8].setFont(ft); keys[13].setFont(ft); keys[16].setFont(ft); keys[18].setFont(ft); keys[19].setFont(ft); // create and register event handler for buttons ButtonHandler handler = new ButtonHandler(); for (int i = 0; i < 20; i++) keys[i].addActionListener(handler); } /** add buttons to a JPanel with a gridLayout and return the JPanel */ private JPanel addButtons() { JPanel panel = new JPanel(); panel.setLayout(new GridLayout(4,5)); // add buttons to JPanel for (int i = 0; i < 20; i++) panel.add(keys[i]); return panel; } /** The button event handler class */ private class ButtonHandler implements ActionListener { public void actionPerformed(ActionEvent e) { // get the label of the buuton causing the event String label = e.getActionCommand(); /* handle button events using the logic specified in a state transition diagram */ if (label.equals("RC")) { // recall numBuffer displayBuffer = new StringBuffer(numBuffer.toString()); displayField.setText(displayBuffer.toString()); } else if (label.equals("BP")) { // backspace display if (displayBuffer.length() != 0 ) { displayBuffer.deleteCharAt(displayBuffer.length()-1); displayField.setText(displayBuffer.toString()); } } else if (label.equals("CL")) { // clear buffers and display numBuffer = new StringBuffer(""); displayBuffer = new StringBuffer(""); opBuffer = ' '; displayField.setText(""); } else if (label.equals("=")) { // the "=" key handleEqual(); } // operators else if (label.equals("+")|| label.equals("-")|| label.equals("*")|| label.equals("/")) { handleOperator(label); } else if (label.equals("+/-")) { // negate display try { double number = Double.parseDouble(displayBuffer.toString()); if (number > 0) { // negate in this case displayBuffer.insert(0, '-'); displayField.setText(displayBuffer.toString()); } else if (number < 0) { displayBuffer.deleteCharAt(0); displayField.setText(displayBuffer.toString()); } } catch (NumberFormatException exp) { /* do nothing if number is not of the proper format */ } } else { // must be digit or decimal point handleDigit(label); } } // end of actionPerformed() /** handle a digit or decimal point input */ private void handleDigit(String digit) { // if the display contains a previously entered operator if (displayBuffer.toString().equals("+")|| displayBuffer.toString().equals("-")|| displayBuffer.toString().equals("*")|| displayBuffer.toString().equals("/")) { // move operator to opBuffer, then display new input opBuffer = displayBuffer.charAt(0); // this is redundant displayBuffer = new StringBuffer(digit); displayField.setText(digit); } else { // otherwise, append new input to display displayBuffer.append(digit); displayField.setText(displayBuffer.toString()); } } /** handle an operator input */ private void handleOperator(String operator) { int code = 0; if (!numBuffer.toString().equals("") && opBuffer != ' ' && !displayBuffer.toString().equals("")) { // perform a previously entered operation code = handleEqual(); // display new operator if no error if (code == 0) { displayBuffer = new StringBuffer(operator); displayField.setText(operator); opBuffer = operator.charAt(0); } } else { // no previous operator saved // move the current display into numBuffer numBuffer = new StringBuffer(displayBuffer.toString()); displayBuffer = new StringBuffer(operator); // display new operator and enter it into opBuffer displayField.setText(operator); opBuffer = operator.charAt(0); } } // end of method handleOperator() /** handle the "=" key input; return 0 for successful operation; return -1 if no operation or if it fails */ private int handleEqual() { // perform a previously entered operation try { // prepare for bad number input double numOne = Double.parseDouble(numBuffer.toString()); double numTwo = Double.parseDouble(displayBuffer.toString()); double result = 0.0; switch (opBuffer) { case '+': result = numOne + numTwo; break; case '-': result = numOne - numTwo; break; case '*': result = numOne * numTwo; break; case '/': // check for divide by zero if (numTwo == 0.0) { displayField.setText("Divide by Zero Error"); return -1; } result = numOne / numTwo; break; } if (opBuffer != ' ') { // if operation performed numBuffer = new StringBuffer(String.valueOf(result)); displayBuffer = new StringBuffer(String.valueOf(result)); displayField.setText(displayBuffer.toString()); opBuffer = ' '; // blank out operator return 0; } else // no operation performed return -1; } catch (NumberFormatException exp) { if (opBuffer != ' ') // operation attempted (12/02/01) displayField.setText("Number Format Exception"); return -1; } } // end of method handleEqual() } // end of class ButtonHandler } // end of class SimpleCalculator