KeyEvent无法识别按下了Shift

Question

I am having following problem, i am trying to restrict users to enter only alphabetical values. Any other value (key pressed) that is not alphabetical will throw error. There are however 3 exceptions, of which two are working fine.
exception1 : Del Key
exception2 : Back Key
exception3 : Shift <- this one is not recognized and i am not sure why

SurnameSearch.addKeyListener(new KeyAdapter(){
        public void keyPressed(KeyEvent e){
            char ch = e.getKeyChar();
                if(Character.isAlphabetic(ch)|| (ch == KeyEvent.VK_BACK_SPACE) || (ch == KeyEvent.VK_DELETE) || (ch == KeyEvent.VK_SHIFT)){/*null*/}
                  else{
                    JOptionPane.showMessageDialog(null, "Only letters are allowed!");
                    SurnameSearch.setText(" ");
            }
        }
    });

Hints appreciated :)

---

@MadProgrammer

Example would be, a user is requested to enter into form his surname, first name, middle name, and mobile telephone number && home phone number. So obviously we dont want numerical values in alphabetic field and vice verse :)

Answer 1

Don't compare the key char with key codes. They are typically different things.

Key codes are a virtual concept used to allow for different keyboard types and input methods.

Instead, use something like e.getKeyCode() == KeyEvent.VK_SHIFT .

If you are trying to restrict the input to any type of text component, KeyListener is not the interface you want. You will want to use a DocumentFilter instead. This will allow y to filter text as it is input to the fields document.

This is a better approach for a number of reasons. The first is, you have no control over the order KeyListeners are notified, meaning the key stroke may have already been submitted to the text component before it reaches your listener. Secondly, if the user pastes text into your field, it will bypass the KeyListener altogether.

Answer 2

That's because the Shift key doesn't have a Unicode key character. It's probably returning KeyEvent.VK_UNDEFINED . Rather, the Shift key modifies other keypresses (ie, it capitalizes them, usually).

From the Javadoc , getKeyChar :

Returns the character associated with the key in this event. For example, the KEY_TYPED event for shift + "a" returns the value for "A".

Instead of using getKeyChar , try getKeyCode , which

Returns the integer keyCode associated with the key in this event.

You will probably also have to use getKeyChar for your isAlphabetic presses (if those matter to you).

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EDIT: Here's a working example:

public static void main(String[] args) {
    JFrame f = new JFrame();
    JButton button = new JButton("Press keys");
    button.addKeyListener(new KeyAdapter() {

        @Override
        public void keyPressed(KeyEvent ke) {
            if (ke.getKeyCode() == KeyEvent.VK_SHIFT) {
                System.out.println("You pressed Shift");
            } else {
                System.out.println("You pressed a non-Shift key");
                // [ more logic ]
            }
        }

    });
    f.add(button, BorderLayout.CENTER);
    f.pack();
    f.setVisible(true);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}