Add & Remove character to text field with one button

Question

I want to make an add & remove ± operator with one button.

So at the beginning ' - ' is supposed to be not available. When I click on ' - ', it should get added in the first line of the text field. If it is already present and we click on it again, it should get removed. How do I do this?

This is the code I have written so far:

private void jButtonActionPerformed(java.awt.event.ActionEvent evt) {                                      
    jTextField.setText( "-" + jTextField.getText());
}

Answer 1

If there is no text, what text is to be added?

Try this out:

    private void jButtonActionPerformed(java.awt.event.ActionEvent evt) 
    {
            if(jTextField.getText().length() != 0)
            {
                jTextField.setText("");
            }
            else
            {
                //Set the text from wherever you are receiving it
            }
    }

When your field is empty, you can set the text to whatever you want, and if it is not, it will be made empty.

Answer 2

did not test this, but it should work:

b.addActionListener(new ActionListener() {

    @Override
    public void actionPerformed(ActionEvent e) {
        if (textField.getText().charAt(0) == '-') {
            String toSet = textField.getText();
            toSet = toSet.substring(0, 0).replace("-", "");
            textField.setText(toSet);
        } else {
            textField.setText("-" + textField.getText());
        }

    }

});

feel free to ask if you have questions

Answer 3

try this:

private void jButtonActionPerformed(java.awt.event.ActionEvent evt) {
        String text = jTextField.getText();
        if (text != null && text.indexOf("-") == 0) {
            text = "+" + text.substring(1, text.length());
        } 
        else if (text != null && text.indexOf("+") == 0) {
            text = "-" + text.substring(1, text.length());
        }
        else {
            text = "-"+(text != null ? text : "");
        }
        jTextField.setText(text);
    }

Answer 4

I'd add on a new ActionListener to the button and define it's code with an @Override statement. This should do the trick:

button.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                String fieldText = textField.getText();

                if (fieldText.substring(0,1).equals("-")){
                    textField.setText(fieldText.substring(1, fieldText.length()));
                } else {
                    textField.setText("-" + fieldText);
                }
            }
        });

Answer 5

A different take on the idea which is a little more efficient, as you're not create so many temporary String objects

btn.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {
        Document doc = field.getDocument();
        try {
            if (doc.getLength() > 0 && doc.getText(0, 1).equals("-")) {
                doc.remove(0, 1);
            } else {
                doc.insertString(0, "-", null);               
            }
        } catch (BadLocationException ex) {
            ex.printStackTrace();
        }
    }
});