MyCalculator.java

import java.awt.*;      // for Graphics
import java.awt.event.*;    // for ActionListener
import javax.swing.*;       // for JFrame

public class MyCalculator {

    /**
    *   Program:    MyCalculator.java by Chris Clarke
    *   Created:    03.06.2009
    *   Purpose:    Calculator with Memory and Square Root.
    *   Modified:   29.10.2011 Memory added. Square root added.
    *           18.05.2012 Converted from Frame to JFrame
    */

    public static void main(String[] args) {
        MyCalculatorJFrame frame = new MyCalculatorJFrame();
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE);
        // Set to a reasonable size.
        frame.setSize(255, 230);
        frame.setVisible(true);
    }
}

class MyCalculatorJFrame extends JFrame implements ActionListener {

    public MyCalculatorJFrame() {
        setTitle("MyCalculator by Chris Clarke");

        // Build control panel.
        JPanel panel = new JPanel();

            btnDigit = new JButton[10];

        for (int i=0; i<10; i++) {
            btnDigit[i] = new JButton(""+i);
            btnDigit[i].addActionListener(this);
                panel.add(btnDigit[i]);
        } // end for

        btnPoint = new JButton(".");
        btnPoint.addActionListener( this);
        panel.add(btnPoint);
        btnEquals = new JButton("=");
        btnEquals.addActionListener(this);
        panel.add(btnEquals);
        tfDisplay = new JTextField(16);
        tfDisplay.setText(""+number);
        panel.add(tfDisplay);
        btnPlus = new JButton("+");
        btnPlus.addActionListener(this);
        panel.add(btnPlus);
        btnMinus = new JButton("-");
        btnMinus.addActionListener(this);
        panel.add(btnMinus);
        btnTimes = new JButton("*");
        btnTimes.addActionListener(this);
        panel.add(btnTimes);
        btnDivide = new JButton("/");
        btnDivide.addActionListener(this);
        panel.add(btnDivide);
        btnMemory = new JButton("M");
        btnMemory.addActionListener(this);
        panel.add(btnMemory);
        btnSquareRoot = new JButton("SqRt");
        btnSquareRoot.addActionListener(this);
        panel.add(btnSquareRoot);
        btnCancelEntry = new JButton("CE");
        btnCancelEntry.addActionListener(this);
        panel.add(btnCancelEntry);
        btnCancelAll = new JButton("AC");
        btnCancelAll.addActionListener(this);
        panel.add(btnCancelAll);
        add(panel, BorderLayout.CENTER);
    }

    public void performCalculation(String operator) {
        if (digit||op) secondNum = number;
        switch (operator) {
            case ("Plus"):
                number = firstNum+secondNum;
                break;
            case ("Minus"):
                number = firstNum-secondNum;
                break;
            case ("Times"):
                number = firstNum*secondNum;
                break;
            case ("Divide"):
                if (secondNum == 0) {
                    tfDisplay.setText("Division by zero error");
                    return;
                } else {
                    number = firstNum/secondNum;
                } // end if
        } // end switch
        reset();
        // display result
        tfDisplay.setText(""+number);
    }

    public void reset() {
        // make a note of the first number
        firstNum = number;
        point = false;
        digit = false;
    }

    public void cancelEntry() {
        number = 0;
        point = false;
        digit = false;
        tfDisplay.setText(""+number);
    }

    public void cancelAll() {
        // do CancelAll stuff
        number = 0;
        operator = "";
        firstNum = 0;
        secondNum = 0;
        point = false;
        digit = false;
        tfDisplay.setText(""+number);
    }

    public void doDecimalPoint() {
        if (!point) {
            if (!digit)
                tfDisplay.setText("0.");
            else
                tfDisplay.setText(tfDisplay.getText()+".");
            point = true;
            digit = true;
        }
    }

    public void doMemoryStuff() {
        // if previous key was "=", set contents of memory to number;
        // otherwise, recall memory and display contents on-screen
        if (equalsKey) {
            mem = number;
        } else {
            number = mem;
            tfDisplay.setText(""+number);
        }
    }

    public void doDigit(ActionEvent e) {
        for (int i=0; i<=9; i++) {
            if (e.getSource() == btnDigit[i]) {
                if (!digit) {
                    tfDisplay.setText("");
                    digit = true;
                }
                tfDisplay.setText(tfDisplay.getText()+i);
                number= Double.parseDouble(tfDisplay.getText());
            }
        }
    }

    public void doSquareRootStuff() {
        double divisor0 = 3.8;              // or any non-zero number
        double divisor1 = 0;
        for (int i = 0; i < 8; i++) {
            //  (10 / M = "" + M = "" / 2 = "" M) repeat
            divisor1 = number / divisor0;
            divisor0 = (divisor0 + divisor1)/2; // the average of the 2 divisors
        }
        number = divisor1;
        tfDisplay.setText(""+number);
    }

    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == btnPlus) {
            // do Plus stuff
            operator = "Plus";
            reset();
            op = true;
            equalsKey=false;
        } else if (e.getSource() == btnMinus) {
            // do Minus stuff
            operator = "Minus";
            reset();
            op = true;
            equalsKey=false;
        } else if (e.getSource() == btnTimes) {
            // do Times stuff
            operator = "Times";
            reset();
            op = true;
            equalsKey=false;
        } else if (e.getSource() == btnDivide) {
            // do Divide stuff
            operator = "Divide";
            reset();
            op = true;
            equalsKey=false;
        } else if (e.getSource() == btnMemory) {
            // do Memory stuff
            doMemoryStuff();
            equalsKey=false;
        } else if (e.getSource() == btnSquareRoot) {
            // do SquareRoot stuff
            doSquareRootStuff();
            equalsKey=false;
        } else if (e.getSource() == btnEquals) {
            // do Equals stuff
            performCalculation(operator);
            equalsKey=true;
        } else if (e.getSource() == btnCancelEntry) {
            // do CancelEntry stuff
            cancelEntry();
            equalsKey=false;
        } else if (e.getSource() == btnCancelAll) {
            // do CancelAll stuff
            cancelAll();
            equalsKey=false;
        } else if (e.getSource() == btnPoint) {
            // do Decimal Point stuff
            doDecimalPoint();
            op = false;
            equalsKey=false;
        } else {
            // do digit stuff
            doDigit(e);
            op = false;
            equalsKey=false;
        } // end if
    } // end actionPerformed()

    private JTextField  tfDisplay;
    private JButton[]   btnDigit;
    private JButton     btnPoint;
    private JButton     btnPlus, btnMinus, btnTimes, btnDivide;
    private JButton     btnEquals, btnMemory, btnSquareRoot;
    private JButton     btnCancelEntry, btnCancelAll;
    private double      number=0;
    private double      firstNum=0;
    private double      secondNum=0;
    private double      mem=0;          // memory
    private String      operator="";
    private boolean     point=false;
    private boolean     digit = false;
    private boolean     op = false;
    private boolean     equalsKey=false;    // true when "=" button clicked
}