Re: Generating & Dispaying JButtons for Calculator

Question

I'm new to Java2 and having problems getting my JButtons to display in my calculator/Currency Converter program.
The JFrame displays with the display textfield at the top but no buttons are generated?
Would appreciate any help in trouble shooting this.
Code as follows;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class KeyPanel extends JPanel
//implements ActionListener
public TextField display;
public JButton[] keypad = new JButton[16]; //there are 16 buttons
on the calculator
public int ADD = 10; // the operator keys are numbered
10..15
public int MINUS = 11; // numeric keys are 0..9
public int MULT = 12;
public int DIV = 13;
public int CLEAR = 14;
public int EQUAL = 15;
public boolean firstDigit;
public int temp1 = 0;
public int temp = 0;
public int result = 0;
public String opr = "";
public KeyPanel()
// SET UP THE KEYPAD GRID
setLayout(new GridLayout(4,4)); buttons on the calculator
// for each array slot create a button and add it to the panel
for (int k=1; k <= 3; k++) {                            //
keypad 1..3
keypad[k]= new JButton( Integer.toString(k) );
add(keypad[k]); //was KeyPanel.add(keypad[k]
keypad[ADD] = new JButton ("+");
add(keypad[ADD]); //addition button
for (int k=4; k <= 6; k++)
{                            // keypad 4..6
keypad[k]= new JButton( Integer.toString(k) );
add(keypad[k]);
keypad[MINUS] = new JButton ("-");
add(keypad[MINUS]); //subtraction button
for (int k=7; k <= 9; k++)
{                            // keypad 7..9
keypad[k]= new JButton( Integer.toString(k) );
add(keypad[k]);
keypad[MULT] = new JButton ("x");
add(keypad[MULT]); //multiplication button
keypad[CLEAR] = new JButton ("C");
add(keypad[CLEAR]);
keypad[0] = new JButton ("0");
add(keypad[0]); //0 button
keypad[EQUAL] = new JButton("=");
add(keypad[EQUAL]); //equals button
keypad[DIV] = new JButton("/");
add(keypad[DIV]); //division button
display = new TextField("",20); //sets the display initially
at 0
display.setEditable (false);
setLayout(new BorderLayout( 10, 10 )); //allows the
positioning of
//display and
key pad
add("North", display);
//add("Center", KeyPanel);
public boolean action(Event e, Object o)
//checks for operator keys
if (e.target == keypad[ADD])
temp1 = temp; //to "save" for calculation
opr = "+";
else if (e.target == keypad[MINUS])
temp1 = temp;
opr = "-";
else if (e.target == keypad[MULT])
temp1 = temp;
opr = "*";
else if (e.target == keypad[DIV])
temp1 = temp;
opr = "/";
else if (e.target == keypad[EQUAL])
result = calculate(temp1,opr,temp);
display.setText(Integer.toString(result)); //does
the calculation
temp = result; //to be able to do an operation on
the result
else if (e.target == keypad[CLEAR])
display.setText("");
temp1 = 0; //resets the temps and display
to 0
temp = 0;
else {                 //numeric buttons...
if (firstDigit) {
display.setText( o.toString() );
firstDigit = false;
temp = Integer.parseInt(display.getText());
//saves the number in a temp
else
display.setText(display.getText() + o.toString());
//for numbers longer than 1 digit
temp = Integer.parseInt(display.getText());
return true;
firstDigit = true;
// GET READY FOR NEXT NUMBER
return true;
public int calculate(int num1,String op, int num2 )
// calculate the numbers
int answers = 0;
if (op == "+")
answers = num1 + num2; //does the calculation for +
else if(op == "-")
answers = num1 - num2; //does the calculation for -
else if(op == "/")
if(num2 == 0)
display.setText("ERROR"); //gives error message
if dividing by 0
else
answers = num1 / num2;
else if(op == "*")
answers = num1 * num2; //does the calculation for *
return answers;
class ButtonFrame extends JFrame
{  public ButtonFrame()
{  setTitle("Currency Converter");
setSize(280, 360);
addWindowListener(new WindowAdapter()
{  public void windowClosing(WindowEvent e)
{  System.exit(0);
Container contentPane = getContentPane();
contentPane.add(new KeyPanel());
public class CurrencyConverter{
public static void main(String args[])
JFrame frame = new ButtonFrame();//was Frame frm = new
Frame("Calculator")
frame.show();
Regards
Synfield

Answer 1

I wish it replaced multiple spaces with &nbsp's. Oh well. It preserves the indentation a bit when I press 'quote original', all though it mangles long lines a little:
public void actionPerformed(ActionEvent evt){
Object source = evt.getSource();
String cmd = evt.getActionCommand();
if (flagNewNum)
display.setText(cmd.toString());
flagNewNum = false; //was firstDigit
temp = Integer.parseInt(display.getText());
etText()); //saves the number in a temp
else
if(display.getText() == "0" +
xt() == "0" + cmd.toString())
display.setText(cmd.toString());
temp =
temp = Integer.parseInt(display.getText());
else
display.setText(display.getText() +
ay.getText() + cmd.toString()); //for numbers longer
than 1 digit
temp =
temp = Integer.parseInt(display.getText());
The above works, except that 'if(display.getText() ==
"0" + cmd.toString())' fails, I want to ovewrite the
default "0" display with the first entry number. What
would be the best way to test this?
Your advice to keep track of display text in a
variable rather than IU components , sounds more
efficient, could you give me some efficient way of
doing this.
Full Code so far for those that are interested as
follows;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
class KeyPanel extends JPanel
implements ActionListener
public TextField display;
public JButton[] keypad = new JButton[16];
on[16]; //there are 16 buttons on the calculator
public int ADD = 10; // the
// the operator keys are numbered 10..15
public int MINUS = 11; // numeric
numeric keys are 0..9
public int MULT = 12;
public int DIV = 13;
public int CLEAR = 14;
public int EQUAL = 15;
public boolean flagNewNum = false;
public int temp1 = 0;
public int temp = 0;
public int result = 0;
public String opr = "";
JPanel keys = new JPanel(new
Panel(new GridLayout(4,4));
public KeyPanel() { // SET UP THE KEYPAD GRID
// keys.getContentPane().setLayout(new
ayout(new GridLayout(4,4)); //buttons on the
calculator
// for each array slot create a button and
button and add it to the panel
for (int k=1; k <= 3; k++) {
<= 3; k++) {                            // keypad
1..3
keypad[k]= new JButton(
pad[k]= new JButton( Integer.toString(k) );
keys.add(keypad[k]); // was
add(keypad[k]); // was KeyPanel.add(keypad[k]
keypad[k].addActionListener(this);
keypad[ADD] = new JButton ("+");
keys.add(keypad[ADD]);
d(keypad[ADD]); //addition button
keypad[ADD].addActionListener(this);
for (int k=4; k <= 6; k++)
{                            // keypad
// keypad 4..6
keypad[k]= new JButton(
keypad[k]= new JButton( Integer.toString(k) );
keys.add(keypad[k]);     
keypad[k].addActionListener(this);
keypad[MINUS] = new JButton ("-");
keys.add(keypad[MINUS]);
keypad[MINUS]); //subtraction button
keypad[MINUS].addActionListener(this);
for (int k=7; k <= 9; k++)
{                            // keypad
// keypad 7..9
keypad[k]= new JButton(
keypad[k]= new JButton( Integer.toString(k) );
keys.add(keypad[k]);
keypad[k].addActionListener(this);
keypad[MULT] = new JButton ("x");
keys.add(keypad[MULT]);
(keypad[MULT]); //multiplication button
keypad[MULT].addActionListener(this);
keypad[CLEAR] = new JButton ("C");
keys.add(keypad[CLEAR]);
keypad[CLEAR].addActionListener(this);
keypad[0] = new JButton ("0");
keys.add(keypad[0]); //0 button
keypad[0].addActionListener(this);
keypad[EQUAL] = new JButton("=");
keys.add(keypad[EQUAL]); //equals
AL]); //equals button
keypad[EQUAL].addActionListener(this);
keypad[DIV] = new JButton("/");
keys.add(keypad[DIV]); //division
); //division button
keypad[DIV].addActionListener(this);
display = new TextField("0",20);
tField("0",20); //sets the display initially at 0
display.setEditable (false);
//sets layout using BorderLayout
setLayout(new BorderLayout());
add(display, BorderLayout.NORTH);
add(keys, BorderLayout.CENTER);
public void actionPerformed(ActionEvent evt){
Object source = evt.getSource();
String cmd = evt.getActionCommand();
//checks for operator keys
if (source == keypad[ADD])
flagNewNum = true;
temp1 = temp; //to "save" for
= temp; //to "save" for calculation
opr = "+";
else if (source == keypad[MINUS])
temp1 = temp;
opr = "-";
else if (source == keypad[MULT])
temp1 = temp;
opr = "*";
else if (source == keypad[DIV])
temp1 = temp;
opr = "/";
else if (source == keypad[EQUAL])
result =
result = calculate(temp1,opr,temp);
display.setText(Integer.toString(result));
g(result)); //does the calculation
temp = result; //to be able
= result; //to be able to do an operation on the
result
else if (source == keypad[CLEAR])
display.setText("0");
temp1 = 0; //resets
0; //resets the temps and display to 0
temp = 0;
else {                 //numeric
//numeric buttons...
if (flagNewNum)
display.setText(cmd.toString());
flagNewNum = false; //was
agNewNum = false; //was firstDigit
temp =
temp =
temp = Integer.parseInt(display.getText());
tText()); //saves the number in a temp
else
if(display.getText() == "0"
(display.getText() == "0" + cmd.toString())
display.setText(cmd.toString());
temp =
temp =
temp =
temp = Integer.parseInt(display.getText());
else
display.setText(display.getText()
xt(display.getText() + cmd.toString()); //for numbers
longer than 1 digit
temp =
temp =
temp =
temp = Integer.parseInt(display.getText());
public int calculate(int num1,String op,
1,String op, int num2 ) // calculate the numbers
int answers = 0;
if (op == "+") {
answers = num1 + num2; //does
um1 + num2; //does the calculation for +
else if(op == "-")
answers = num1 - num2; //does
num1 - num2; //does the calculation for -
else if(op == "/")
if(num2 == 0)
display.setText("ERROR");
display.setText("ERROR"); //gives error message if
dividing by 0
else
answers = num1 / num2;
else if(op == "*")
answers = num1 * num2; //does
num1 * num2; //does the calculation for *
return answers;
class ButtonFrame extends JFrame
{  public ButtonFrame()
{  setTitle("Currency Converter");
setSize(280, 360);
addWindowListener(new WindowAdapter()
{  public void windowClosing(WindowEvent e)
{  System.exit(0);
Container contentPane = getContentPane();
contentPane.add(new KeyPanel());
public class CurrencyConverter{
public static void main(String args[])
JFrame frame = new ButtonFrame();
frame.show();