Java - How to enforce JTextField to have alphanumeric values

Question

I want the JTextField to accept only Letters and Numbers. But it SHOULD contain both. It should not contain not letters only nor numbers only.

Answer 1

1) Try adding a key listener to your text field. See if it helps.
Once the user has finished typing, check the values of both flags.

private boolean hasLetter = false;
private boolean hasDigit = false;

public void keyTyped(KeyEvent evt) {
        char c = evt.getKeyChar();

        if (Character.isLetter(c)) {
            // OK
            hasLetter = true;
        } else if (Character.isDigit(c)) {
            // OK
            hasDigit = true;                
        } else {
            // Ignore this character
            evt.consume();
        }
}

2) Alternatively, just accept any character and validate at the very end
when the user has finished typing. For this you can use a regular expression.

"a1b2c".matches("^(?=.*[A-Za-z])(?=.*[0-9])[A-Za-z0-9]+$")
"123".matches("^(?=.*[A-Za-z])(?=.*[0-9])[A-Za-z0-9]+$")
"abc".matches("^(?=.*[A-Za-z])(?=.*[0-9])[A-Za-z0-9]+$")