{

// number of digits (inclusive of decimal point) allowed in the display

public static final int CAPACITY = 15;

// private variables

private JFrame frame;

private JTextArea display;

// boolean set to true if number already has a decimal point

private Boolean decPoint = false;

// boolean set to true if an operator has been clicked

private Boolean operators;

// string representing addend, subtractor, multiplicator or numerator

private StringBuilder num1 = new StringBuilder();

// string representing addend, subtractor, multiplicator or denominator

private StringBuilder num2 = new StringBuilder();

// Double representing addend, subtractor, multiplicator or numerator

private Double firstNum = null;

// Double representing addend, subtractor, multiplicator or denominator

private Double secondNum = null;

// String representing an operator (+, -, *, /, or square root)

private String operator = null;

private Boolean oldOp = false;

// indicates whether the display should be cleared

private Boolean doClear;

// array of number buttons

private JButton [] jb = new JButton[10];

//operator buttons

private JButton clear, root, plus, minus, div, mult, equals, point;

/****

* Constructor. Sets up user interface and initializations

*/

public Secondtry()

{

operators = true;

doClear = false;

frame = new JFrame ("Calculator");

frame.setLayout( new BorderLayout( 10, 10 ));

display = new JTextArea();

display.setSize(245, 100);

display.setFont (new Font ("SansSerif", Font.BOLD, 28));

display.setComponentOrientation(ComponentOrientation.RIGHT_TO_LEFT);

// create the numeric buttons for calculator

for (int i = 0; i < 10; i++ )

{

jb[i] = new JButton ("" + (i));

jb[i].addActionListener(this);

jb[i].setFont (new Font ("SansSerif", Font.BOLD, 14));

}

// create the square root button

root = new JButton("\u221A");

root.addActionListener(this);

root.setFont (new Font ("SansSerif", Font.BOLD, 14));

// create the clear button

clear = new JButton("C");

clear.addActionListener(this);

clear.setFont (new Font ("SansSerif", Font.BOLD, 14));

// create the plus button

plus = new JButton("\u002B");

plus.addActionListener(this);

plus.setFont (new Font ("SansSerif", Font.BOLD, 14));

// create the minus button

minus = new JButton("\u002D");

minus.addActionListener(this);

minus.setFont (new Font ("SansSerif", Font.BOLD, 14));

// create the multiply button

mult = new JButton("\u002A");

mult.addActionListener(this);

mult.setFont (new Font ("SansSerif", Font.BOLD, 14));

// create the division button

div = new JButton("\u002F");

div.addActionListener(this);

div.setFont (new Font ("SansSerif", Font.BOLD, 14));

// create the equals button

equals = new JButton("\u003D");

equals.addActionListener(this);

equals.setFont (new Font ("SansSerif", Font.BOLD, 14));

equals.setPreferredSize(new Dimension(50, 60));

// create the point button

point = new JButton("\u002E");

point.addActionListener(this);

point.setFont (new Font ("SansSerif", Font.BOLD, 14));

// button grid

JPanel buttons = new JPanel(new GridLayout(5, 4, 4, 4));

// add buttons to grid

buttons.add(clear);

buttons.add(root);

buttons.add(div);

buttons.add(mult);

// add numeric buttons to grid

for (int i = 7; i < 10; i++)

buttons.add ( jb[i] );

buttons.add(minus);

// add numeric buttons to grid

for (int i = 4; i < 7; i++)

buttons.add ( jb[i] );

buttons.add(plus);

// add numeric buttons to grid

for (int i = 1; i < 4; i++)

buttons.add ( jb[i] );

buttons.add(equals);

buttons.add(jb[0]);

buttons.add(point);

frame.add (display, BorderLayout.CENTER);

frame.add (buttons, BorderLayout.SOUTH);

frame.setSize (300, 400);

frame.setVisible (true);

frame.setResizable(false);

frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE);

}

public void actionPerformed( ActionEvent ae )

{

// clear display if new number is to be entered

if(doClear)

display.setText(null);

// if decimal point is entered for the first time in number

if((ae.getSource() == point) && decPoint == false) {

display.append(".");

// disallow more decimal points

decPoint = true;

}

// if decimal point is the first in a number, display "0."

if (display.getText().equals("."))

display.setText("0.");

// check if a digit was clicked

for (int i = 0; i < 10; i++) {

// append digits to number while number is less than 15 digits long

if((ae.getSource() == jb[i]) && (display.getText().length() < 15)) {

display.append(((JButton)ae.getSource()).getText());

// disallow leading zeros

if (display.getText().equals("0"))

display.setText("0.");

// store as a Double

secondNum = Double.parseDouble(display.getText());

System.out.println("SecondNum is: " + secondNum);

doClear = false;

// only if you click another digit

oldOp = false;

}

}

// check if an operator was clicked

if((ae.getSource() == plus) || (ae.getSource() == minus) ||

(ae.getSource() == div) || (ae.getSource() == mult)) {

decPoint = false;

if(oldOp == false) {

// if this is the first time an operator was clicked

if (operators) {

// the number last entered becomes the first number

firstNum = secondNum;

System.out.println("firstNum is: " + secondNum);

}

else {

calc();

}

// store the operator that was clicked

JButton temp=(JButton)ae.getSource();

operator = temp.getText();

System.out.println("Operator is: " + operator);

operators = false;

doClear = true;

oldOp = true;

}

// if an operator was clicked without a digit having been entered between

else {

// store the operator that was clicked

JButton temp=(JButton)ae.getSource();

operator = temp.getText();

System.out.println("Operator is: " + operator);

display.setText(String.valueOf(firstNum));

}

}

if(ae.getSource() == root) {

squareRoot();

decPoint = false;

}

if(ae.getSource() == clear) {

clear();

}

if(ae.getSource() == equals) {

calc();

}

}

public void squareRoot() {

if (secondNum == 0.0) {

display.setText("ERROR");

firstNum = 0.0;

secondNum = 0.0;

operators = true;

doClear = true;

}

else {

secondNum = Math.sqrt(secondNum);

display.setText(String.valueOf(secondNum));

}

}

public void calc() {

if(operator== "+") {

firstNum += secondNum;

System.out.println("firstNum plus secondNum is: " + firstNum); }

if(operator == "-"){

firstNum -= secondNum;

System.out.println("firstNum minus secondNum is: " + firstNum);}

if(operator == "*") {

firstNum *= secondNum;

System.out.println("firstNum times secondNum is: " + firstNum);}

if((operator == "/") && secondNum != 0.0){

System.out.println("firstNum div by secondNum is: " + firstNum);

firstNum /= secondNum;}

if((operator == "/") && secondNum == 0.0){

display.setText("ERROR");

System.out.println(display.getText());

firstNum = 0.0;

secondNum = 0.0;

operators = true;

doClear = true;

}

if (!(display.getText().equals("ERROR"))) {

operators = true;

decPoint = false;

display.setText(String.valueOf(firstNum));

secondNum = firstNum;

System.out.println("SecondNum is: " + firstNum);

}

}

public void clear() {

firstNum = 0.0;

secondNum = 0.0;

operators = true;

display.setText(null);

}

public static void main(String args[])

{

Secondtry sec = new Secondtry ();

}

}