String comparison for button events

I have a String named updatedDisplay that is set to empty in the constructor. The buttons[] are JButtons and alarmCode is a String field.

I want the user to press four buttons (and they should be c开发者_如何学Gooncatenated and stored in the updatedDisplay field).

The checkCode() method is executed to try match updatedDisplay against alarmCode. Trouble is, they never match. I think it may be something to do with a "space" when I originally declare my updatedDisplay as follows:

private String updatedDisplay = " ";

The updatedDisplay field doesn't seem to be storing the e.getActionCommand() value.

//add actionListeners to each button (except the "clear" button) to display value on screen
for (int i = 0; i< (buttons.length -1); i++) {
  buttons[i].addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e)
          {
          //store the name of the button in a local variable
          String command = e.getActionCommand();

          System.out.println("You clicked " + command);

          updatedDisplay = updatedDisplay + command;
          //updatedDisplay = command;
          System.out.println (updatedDisplay);

          screen.setText(updatedDisplay);
}
     });}

I have an armButton that, when pressed, should trigger the checkCode() method. The method checks if updatedDisplay and alarmCode are equal:

//add actionListener to the arm button
armButton.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) 
        {
         checkCode(); 
        }
    });

checkCode():

public void checkCode() {
//check if user entered the correct code
if (updatedDisplay == alarmCode)
{
  updatedDisplay =  "System Armed!";
  screen.setText(updatedDisplay);
}
else
{
  updatedDisplay  = "Incorrect Code, Try again!";
  screen.setText(updatedDisplay);
}
}

Even when I output the button presses to the terminal window they look right - but as I said, I suspect a "space" is being entered at the start.

Any ideas?

Solution

Try:

if( updatedDisplay.equals( alarmCode ) { // ...

Comparison

To understand this, read:

http://leepoint.net/notes-java/data/expressions/22compareobjects.html

Summary

Since updatedDate and alarmCode are object references, you must ask the objects to compare their values. You can think of them as pointers whose values are locations in memory that contain strings. Rather than comparing the value of the pointers (references), you want to compare the text that starts at that memory location.