subtracting the last number from a string

Hi, i'm creating a basic calculator application with NetBeans 6.0 and I'm having trouble getting the backspace button to work. I've been trying the code

display = (display.length -1);

where display is the number that the user input, but i'm getting the error of

"operator - cannot be applied to java.lang.string.length,int"

Display is set as a string and later converted to a double..


code dealing with the display variable is:
edit: top part of the code with all the display = is variations i was trying to play around with

Code:

---

private void backspace(String display)
{
  // display = display.Remove(display.Length - 1);
    display = String.valueOf(display);
    display = ((display.length)- (one));
    display = (display.length -1);
   
}

private void operation(char currentOp)
{
  if (!operatorPressed)
  {
        switch( previousOperation )
        {
            case 'B':
                previousDisplay = display;
                break;
            case '=':
                previousDisplay = String.valueOf(
                        Double.parseDouble(previousDisplay)
                        +
                        Double.parseDouble(display));
                display = previousDisplay;
                jTextField.setText(display);
                break;
            case '+':
                previousDisplay = String.valueOf(
                        Double.parseDouble(previousDisplay)
                        +
                        Double.parseDouble(display));
                display = previousDisplay;
                jTextField.setText(display);
                break;
            case '-':
                previousDisplay = String.valueOf(
                        Double.parseDouble(previousDisplay)
                        -
                        Double.parseDouble(display));
                display = previousDisplay;
                jTextField.setText(display);
                break;
            case '*':
                previousDisplay = String.valueOf(
                        Double.parseDouble(previousDisplay)
                        *
                        Double.parseDouble(display));
                display = previousDisplay;
                jTextField.setText(display);
                break;
            case '/':
                previousDisplay = String.valueOf(
                        Double.parseDouble(previousDisplay)
                        /
                        Double.parseDouble(display));
                display = previousDisplay;
                jTextField.setText(display);
                break;
        }
        if (currentOp == '=')
        {
            display = "0";
            previousDisplay = "0";
            previousOperation = 'B';
        }
        previousOperation = currentOp;
        operatorPressed = true;
    }
}

---

also, my decimal isn't working correctly.. if i do 9.6 + .4 it shows 9.6. + 4 = 13.6 - any ideas?

Code:

---

private void decimaldot(String num)
{
    jTextField.setText("0");
    jTextField.setText(display + '.');
    display = display + '.';

}

---

thanks in advance

Use display.length() because length is a method not an attribute