DocumentListener Java, How do I prevent empty string in JTextBox?
As @HFOE suggests, InputVerifier is the right choice, but verify() “should have no side effects.” Instead, invoke calcProduct() in shouldYieldFocus(). /** * @see http://stackoverflow.com/a/11818946/230513 */ private class MyInputVerifier extends InputVerifier { private JTextField field; private double value; public MyInputVerifier(JTextField field) { this.field = field; } @Override public boolean shouldYieldFocus(JComponent input) { if (verify(input)) { field.setText(String.valueOf(value)); … Read more