How to create a calculator using stack in Java?

I am creating rpn calculator by using stack.I don't know why my codes does not work in stacks.can someone help to fix my codes.I know it's about stack.here is my codes.

/**

 

*/

 import java.util.Stack;

 import java.awt.*;

 import java.awt.event.*;

 import javax.swing.*;

 import java.math.*;

 

public class JavaCalculator extends JFrame{

 Stack s = new Stack();

 

private JFrame f;

 private JPanel p1,p2;

 private JTextField jtfMain;

 private JButton jbtnOn, jbtnMRC, jbtnMminus, jbtnMadd, jbtnDivide, jbtnOff, jbtnSeven, jbtnEight, jbtnNine, jbtnMultiply,

 jbtnSqrt, jbtnFour, jbtnFive, jbtnSix, jbtnMinus, jbtnSq, jbtnOne, jbtnTwo, jbtnThree, jbtnPlus, jbtn1x, jbtnZero, jbtnDecimal,

 jbtnEqual, jbtnEnter;

 

public JavaCalculator() {

 



setSize(400,190);

 setTitle("Reverse Polish Notation Calculator");

 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

 setLayout(new BorderLayout());

 

jtfMain = new JTextField("");

 

jbtnOn = new JButton("ON/AC");

 jbtnMRC = new JButton("MRC");

 jbtnMminus = new JButton("M-");

 jbtnMadd = new JButton("M+");

 jbtnDivide = new JButton("/");

 jbtnOff = new JButton("OFF");

 jbtnSeven = new JButton("7");

 jbtnEight = new JButton("8");

 jbtnNine = new JButton("9");

 jbtnMultiply = new JButton("X");

 jbtnSqrt = new JButton("SQRT");

 jbtnFour = new JButton("4");

 jbtnFive = new JButton("5");

 jbtnSix = new JButton("6");

 jbtnMinus = new JButton("-");

 jbtnSq = new JButton("SQ");

 jbtnOne = new JButton("1");

 jbtnTwo = new JButton("2");

 jbtnThree = new JButton("3");

 jbtnPlus = new JButton("+");

 jbtn1x = new JButton("1/x");

 jbtnZero = new JButton("0");

 jbtnDecimal = new JButton(".");

 jbtnEqual = new JButton("=");

 jbtnEnter = new JButton("ENTER");

 

p1 = new JPanel();

 p1.setLayout(new GridLayout(1,1));

 

p2 = new JPanel();

 p2.setLayout(new GridLayout(5,5));

 

p1.add(jtfMain);

 

p2.add(jbtnOn);

 p2.add(jbtnMRC);

 p2.add(jbtnMadd);

 p2.add(jbtnMminus);

 p2.add(jbtnDivide);

 p2.add(jbtnSeven);

 p2.add(jbtnEight);

 p2.add(jbtnNine);

 p2.add(jbtnMultiply);

 p2.add(jbtnSqrt);

 p2.add(jbtnFour);

 p2.add(jbtnFive);

 p2.add(jbtnSix);

 p2.add(jbtnMinus);

 p2.add(jbtnSq);

 p2.add(jbtnOne);

 p2.add(jbtnTwo);

 p2.add(jbtnThree);

 p2.add(jbtnPlus);

 p2.add(jbtn1x);

 p2.add(jbtnZero);

 p2.add(jbtnDecimal);

 p2.add(jbtnEqual);

 p2.add(jbtnEnter);

 p2.add(jbtnOff);

 

jbtnOn.addActionListener(new ButtonHandler());

 jbtnMRC.addActionListener(new ButtonHandler());

 jbtnMminus.addActionListener(new ButtonHandler());

 jbtnDivide.addActionListener(new ButtonHandler());

 jbtnOff.addActionListener(new ButtonHandler());

 jbtnSeven.addActionListener(new ButtonHandler());

 jbtnEight.addActionListener(new ButtonHandler());

 jbtnNine.addActionListener(new ButtonHandler());

 jbtnMultiply.addActionListener(new ButtonHandler());

 jbtnSqrt.addActionListener(new ButtonHandler());

 jbtnFour.addActionListener(new ButtonHandler());

 jbtnFive.addActionListener(new ButtonHandler());

 jbtnSix.addActionListener(new ButtonHandler());

 jbtnMinus.addActionListener(new ButtonHandler());

 jbtnSq.addActionListener(new ButtonHandler());

 jbtnOne.addActionListener(new ButtonHandler());

 jbtnTwo.addActionListener(new ButtonHandler());

 jbtnThree.addActionListener(new ButtonHandler());

 jbtnPlus.addActionListener(new ButtonHandler());

 jbtn1x.addActionListener(new ButtonHandler());

 jbtnZero.addActionListener(new ButtonHandler());

 jbtnDecimal.addActionListener(new ButtonHandler());

 jbtnEqual.addActionListener(new ButtonHandler());

 jbtnEnter.addActionListener(new ButtonHandler());

 

add(p1, BorderLayout.NORTH);

 add(p2, BorderLayout.CENTER);

 

setVisible(true);

 }

 

public class ButtonHandler implements ActionListener

 {

 public void actionPerformed(ActionEvent evt)

 {

 if(evt.getSource()== jbtnOn)

 {

 jtfMain.setText("");

 }

 else if(evt.getSource()== jbtnOne)

 {

 s.push("1");

 

jtfMain.setText(jtfMain.getText() + "1");

 

}

 else if(evt.getSource()== jbtnTwo)

 {

 s.push("2");

 jtfMain.setText(jtfMain.getText() + "2");

 

}

 else if(evt.getSource()== jbtnThree)

 {

 s.push("3");

 jtfMain.setText(jtfMain.getText() + "3");

 

}

 else if(evt.getSource()== jbtnFour)

 {

 s.push("4");

 jtfMain.setText(jtfMain.getText() + "4");

 

}

 else if(evt.getSource()== jbtnFive)

 {

 s.push("5");

 jtfMain.setText(jtfMain.getText() + "5");

 

}

 else if(evt.getSource()== jbtnSix)

 {

 s.push("6");

 jtfMain.setText(jtfMain.getText() + "6");

 

}

 else if(evt.getSource()== jbtnSeven)

 {

 s.push("7");

 jtfMain.setText(jtfMain.getText() + "7");

 

}

 else if(evt.getSource()== jbtnEight)

 {

 s.push("8");

 

jtfMain.setText(jtfMain.getText() + "8");

 

}

 else if(evt.getSource()== jbtnNine)

 {

 s.push("9");

 jtfMain.setText(jtfMain.getText() + "9");

 

}

 else if(evt.getSource()== jbtnZero)

 {

 s.push("0");

 jtfMain.setText(jtfMain.getText() + "0");

 

}

 else if(evt.getSource()== jbtnDivide)

 {

 s.push("/");

 jtfMain.setText(jtfMain.getText() + "/");

 

}

 else if(evt.getSource()== jbtnMultiply)

 {

 s.push("X");

 jtfMain.setText(jtfMain.getText() + "X");

 

}

 else if(evt.getSource()== jbtnPlus)

 {

 s.push("+");

 jtfMain.setText(jtfMain.getText() + "+");

 


}

 else if(evt.getSource()== jbtnMinus)

 {

 s.push("-");

 jtfMain.setText(jtfMain.getText() + "-");

 


}

 else if(evt.getSource() == jbtnEnter)

 {

 s.push(" ");

 jtfMain.setText(evaluateExpr(jtfMain.getText()) + " ");

 }

 }

 }

 //Implement RPN algorithm

 //pre-condition: The given input is in post-fix notation with tokens separated by a single space.

 //Assumes binary operators only

 

private int evaluateExpr(String expr)

 {

 for(String token: expr.split(" "))

 {

 if(!isOperator(token))

 s.push(token);

 else

 {

 

}

 }

 return s.pop();

 }

 

public static void main(String[] args) {

 JavaCalculator main = new JavaCalculator();

 }

 }

Edited by Alyn, 02 November 2011 - 02:33 PM.
added code tag