import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
///////////////////////////////////////////////////////////////////// class Calc
class Calc extends JFrame {
//================================================================ constants
private static final Font BIGGER_FONT = new Font("monspaced", Font.PLAIN, 20);
//=================================================================== fields
//... Component referenced during execution
private JTextField _displayField; // display result / input.
//... Variables representing state of the calculator
private boolean _startNumber = true; // true: num key next
private String _previousOp = "="; // previous operation
private CalcLogic _logic = new CalcLogic(); // The internal calculator.
//============================================================== method main
public static void main(String[] args) {
//... Set the Look and Feel to that of system we're running on.
try {
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
} catch (Exception unused) {
; // Ignore exception because we can't do anything. Will use default.
}
//... Create the window.
Calc window = new Calc();
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setVisible(true);
}
//============================================================== constructor
public Calc() {
//... Set attributes of the display field
_displayField = new JTextField("0", 12);
_displayField.setHorizontalAlignment(JTextField.RIGHT);
_displayField.setFont(BIGGER_FONT);
//... Create and set attributes of clear button
JButton clearButton = new JButton("Clear");
clearButton.setFont(BIGGER_FONT);
clearButton.addActionListener(new ClearListener());
//... Use one listener for all numeric keys.
ActionListener numListener = new NumListener();
//... Layout numeric keys in a grid. Generate the buttons
// in a loop from the chars in a string.
String buttonOrder = "789456123 0 ";
JPanel buttonPanel = new JPanel();
buttonPanel.setLayout(new GridLayout(5, 3, 2, 2));
for (int i = 0; i < buttonOrder.length(); i++) {
String keyTop = buttonOrder.substring(i, i+1);
JButton b = new JButton(keyTop);
if (keyTop.equals(" ")) {
//... Put a dummy button in this position.
b.setEnabled(false);
} else {
//... Put a digit button in the interface.
b.addActionListener(numListener);
b.setFont(BIGGER_FONT);
}
buttonPanel.add(b);
}
//... One ActionListener to use for all operator buttons.
ActionListener opListener = new OpListener();
//... Create panel with gridlayout to hold operator buttons.
// Use array of button names to create buttons in a loop.
JPanel opPanel = new JPanel();
opPanel.setLayout(new GridLayout(5, 1, 2, 2));
String[] opOrder = {"+", "-", "*", "/", "="};
for (int i = 0; i < opOrder.length; i++) {
JButton b = new JButton(opOrder[i]);
b.addActionListener(opListener);
b.setFont(BIGGER_FONT);
opPanel.add(b);
}
//... Put Clear button in flow layout to keep from expanding.
JPanel clearPanel = new JPanel();
clearPanel.setLayout(new FlowLayout());
clearPanel.add(clearButton);
//... Layout the top-level content panel.
JPanel content = new JPanel();
content.setLayout(new BorderLayout(5, 5));
content.add(_displayField, BorderLayout.NORTH );
content.add(buttonPanel , BorderLayout.CENTER);
content.add(opPanel , BorderLayout.EAST );
content.add(clearPanel , BorderLayout.SOUTH );
content.setBorder(BorderFactory.createEmptyBorder(10,10,10,10));
//... Finish building the window (JFrame)
this.setContentPane(content);
this.pack();
this.setTitle("Simple Calc");
this.setResizable(false);
this.setLocationRelativeTo(null);
}//end constructor
//============================================================== actionClear
/** Called by Clear btn action listener and elsewhere.*/
private void actionClear() {
_startNumber = true; // Expecting number, not op.
_displayField.setText("0");
_previousOp = "=";
_logic.setTotal("0");
}
//////////////////////////////////////////// inner listener class OpListener
/** Listener for all op buttons. */
class OpListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
// The calculator is always in one of two states.
// 1. A number must be entered -- an operator is wrong.
// 2. An operator must be entered.
if (_startNumber) { // Error: needed number, not operator
//... In this state we're expecting a number, but got an operator.
actionClear();
_displayField.setText("ERROR - No operator");
} else {
//... We're expecting an operator.
_startNumber = true; // Next thing must be a number
try {
// Get value from display field, convert, do prev op
// If this is the first op, _previousOp will be =.
String displayText = _displayField.getText();
if (_previousOp.equals("=")) {
_logic.setTotal(displayText);
} else if (_previousOp.equals("+")) {
_logic.add(displayText);
} else if (_previousOp.equals("-")) {
_logic.subtract(displayText);
} else if (_previousOp.equals("*")) {
_logic.multiply(displayText);
} else if (_previousOp.equals("/")) {
_logic.divide(displayText);
}
_displayField.setText("" + _logic.getTotalString());
} catch (NumberFormatException ex) {
actionClear();
_displayField.setText("Error");
}
//... set _previousOp for the next operator.
_previousOp = e.getActionCommand();
}//endif _startNumber
}//endmethod
}//end class
//////////////////////////////////// inner listener class ClearListener
/** Action listener for numeric keys */
class NumListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
String digit = e.getActionCommand(); // Get text from button
if (_startNumber) {
//... This is the first digit, clear field and set
_displayField.setText(digit);
_startNumber = false;
} else {
//... Add this digit to the end of the display field
_displayField.setText(_displayField.getText() + digit);
}
}
}
//////////////////////////////////// inner listener class ClearListener
class ClearListener implements ActionListener {
public void actionPerformed(ActionEvent e) {
actionClear();
}
}
}
---------------------------------------------
public class CalcLogic {
//-- Instance variables.
private int _currentTotal; // The current total is all we need to remember.
/** Constructor */
public CalcLogic() {
_currentTotal = 0;
}
public String getTotalString() {
return "" + _currentTotal;
}
public void setTotal(String n) {
_currentTotal = convertToNumber(n);
}
public void add(String n) {
_currentTotal += convertToNumber(n);
}
public void subtract(String n) {
_currentTotal -= convertToNumber(n);
}
public void multiply(String n) {
_currentTotal *= convertToNumber(n);
}
public void divide(String n) {
_currentTotal /= convertToNumber(n);
}
private int convertToNumber(String n) {
return Integer.parseInt(n);
}
}
