Validation on swing

Question

Plesae i need to make validation on text filed so user can insert null if user insert null on text files message box displayed to user

Answer 1

Get the text from the component and check if it's null? if it's null create a JOptionPane or something like that to inform the user that he didn't enter anything. Or you could use Regex's if you want to check what the user submitted.

Edit: pseudocode example
For swing components, and I'm assuming you're using a JTextField you could do something like:

if(submitbutton is triggered){
if(textField.getText().isEmpty()){
JOptionPane.showMessageDialog(component,
    "You did not enter anything in the Textfield, please do so",
    "Empty Textfield",
    JOptionPane.PLAIN_MESSAGE);
return;
}}