JTextField take twice the input, but why?

I wanna make a programmable calculator, i got the basic GUI, and now i'm trying to set up the buttons, and the display. My display text will be "0" basically and if the user type in a number, that number should to be displayed. I tried to do it with KeyListener, but if i press a key it will display the key twice. Why?

textField.addKeyListener(new KeyListener()
boolean newNumber = true;

public void keyTyped(KeyEvent e)


public void keyPressed(KeyEvent e)
int keyCode = e.getKeyCode();


if(keyCode == e.VK_BACK_SPACE && textField.getText().length() == 1)
textField.setText("0");
newNumber = true;


if(textField.getText().equals("0") && newNumber)
textField.setText(KeyEvent.getKeyText(keyCode));
newNumber = false;



public void keyReleased(KeyEvent e)


);


Before input:

After "1" input:

KeyListener

DocumentFilter

keyPressed

JTextField

Document

1

KeyListener

ScriptEngine

2 Answers
2

Here a simple solution:

If you use keyPressed, you have to do something in keyReleased and this become
complicated. keyTyped is a more simple way.

keyPressed

keyReleased

keyTyped

You can use e.consume() to prevent having the double digit inserted.

e.consume()

textField.addKeyListener(new KeyListener()

int codeDelete = KeyEvent.getExtendedKeyCodeForChar(KeyEvent.VK_DELETE);
int codeBackSpace = KeyEvent.getExtendedKeyCodeForChar(KeyEvent.VK_BACK_SPACE);

@Override
public void keyTyped(KeyEvent e)

char keyChar = e.getKeyChar();

if (textField.getText().length() == 0)
textField.setText("0");

else if (textField.getText().equals("0") && keyChar != codeDelete && keyChar != codeBackSpace)
textField.setText(String.valueOf(e.getKeyChar()));
e.consume();



@Override
public void keyPressed(KeyEvent e)


@Override
public void keyReleased(KeyEvent e)


);


KeyEvent.getExtendedKeyCodeForChar(KeyEvent.VK_DELETE)

KeyEvent.getExtendedKeyCodeForChar(KeyEvent.VK_BACK_SPACE)

For doing that, I derive PlainDocument like this:

import java.awt.EventQueue;
import java.util.regex.Pattern;

import javax.swing.JTextField;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.PlainDocument;

public class DigitDocument extends PlainDocument

private static final long serialVersionUID = 1L;
protected static final Pattern patternStartZero = Pattern.compile("^0.+");

protected final JTextField textField;

private final int limit;
private final Runnable runnableFormat;

public DigitDocument(JTextField textField, int limit)

super();

this.textField = textField;
this.limit = limit;

runnableFormat = new Runnable()

@Override
public void run()

String text = textField.getText();

if (text.length() == 0)
textField.setText("0");

else if (patternStartZero.matcher(text).matches())
textField.setText(text.replaceAll("^0+", ""));


;


@Override
public void insertString(int offset, String str, AttributeSet attr) throws BadLocationException

str = str.replaceAll("[^0-9]", "");

if (str.length() == 0)
return;

else if ((getLength() + str.length()) <= limit)
super.insertString(offset, str, attr);

EventQueue.invokeLater(runnableFormat);


@Override
public void remove(int offs, int len) throws BadLocationException
if (!"0".equals(textField.getText()))
super.remove(offs, len);

EventQueue.invokeLater(runnableFormat);




The usage is:

textField.setDocument(new DigitDocument(textField, 10));
textField.setText("0");


In DigitDocument,

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