need help with my java calculator, about the key listener. its allows me to input using keyboard. but the answers are always "ERROR".. but when i try to use the mouse. it works fine. having problem with the keylistener. please help
CALC
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
class Calc{
public static void main(String[] args){
JFrame window = new JFrame("Calculator");
window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
window.setContentPane(new CalcGUI());
window.pack();
window.show();
}
}CALC GUI
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
class CalcGUI extends JPanel{
private JTextField _displayField;
private boolean _startNumber = true;
private double _resultValue = 0;
private String _previousOp = "=";
private static final Font BIGGER_FONT = new Font("monspaced",Font.PLAIN,24);
public CalcGUI() {
_displayField = new JTextField("0",12);
_displayField.setHorizontalAlignment(JTextField.RIGHT);
_displayField.setFont(BIGGER_FONT);
JButton clearButton = new JButton("CLEAR");
clearButton.setFont(BIGGER_FONT);
clearButton.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e){
action_clear();
};
}
);
ActionListener numListener =
new ActionListener(){
public void actionPerformed(ActionEvent e){
action_num(e);
}
};
String buttonOrder = "123456789 0.";
JPanel buttonPanel = new JPanel(new GridLayout(5,3));
for(int i=0;i<buttonOrder.length();i++){
String keyTop = buttonOrder.substring(i,i+1);
if(keyTop.equals("")){
buttonPanel.add(new Label(""));
}else{
JButton b = new JButton(keyTop);
b.addActionListener(numListener);
b.setFont(BIGGER_FONT);
buttonPanel.add(b);
}
}
ActionListener opListener =
new ActionListener(){
public void actionPerformed(ActionEvent e){
action_op(e);
}
};
JPanel opPanel = new JPanel(new GridLayout(5,1));
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);
}
this.setLayout(new BorderLayout());
this.add(_displayField,BorderLayout.NORTH);
this.add(buttonPanel,BorderLayout.CENTER);
this.add(opPanel,BorderLayout.EAST);
this.add(clearButton,BorderLayout.SOUTH);
}
private void action_op(ActionEvent e){
if(_startNumber){
action_clear();
_displayField.setText("ERROR");
}else{
_startNumber = true;
try{
double currentValue = Double.parseDouble(_displayField.getText());
if(_previousOp.equals("=")){
_resultValue = currentValue;
}else if(_previousOp.equals("+")){
_resultValue += currentValue;
}else if(_previousOp.equals("-")){
_resultValue -= currentValue;
}else if(_previousOp.equals("*")){
_resultValue *= currentValue;
}else if(_previousOp.equals("/")){
_resultValue /=currentValue;
}else if(_previousOp.equals("%")){
_resultValue %= currentValue;
}
_displayField.setText(""+_resultValue);
}catch(NumberFormatException ex){
action_clear();
_displayField.setText("ERROR");
}
_previousOp = e.getActionCommand();
}
}
private void action_num(ActionEvent e){
String digit = e.getActionCommand();
if(_startNumber){
_displayField.setText(digit);
_startNumber=false;
}else{
_displayField.setText(_displayField.getText()+digit);
}
}
public void action_clear()
{
_startNumber = true;
_displayField.setText("0");
_resultValue = 0;
_previousOp = "=";
}
}