How to point out which jTextfield is empty

Question

I have this code sample to see which Jtextfield is empty. I have attached a image of my application too. All I need to know is that, when a user was not entering the details in a specific jTextfield, and click "Register" button, I want the user to be informed about his mistake/s like;

"You haven't entered Student Middle Name" or "You have not entered Student Address" or "You haven't entered Student middle name and Address"

I want the user to inform SPECIFICALLY which jTextfield/s is/are EMPTY and set its/Their background/s RED and stop saving the details into database until he fills all the JtextFields. I have tried many codes but any of it didn't work :(

Here's my Code. I have used the array to check the Jtextfield/s are empty or not, but I don't know how to inform the user which Jtextfield/s is/are causing the problem. Please Help Me :(

public void checkEmpty() {
    String fname = jTextField1.getText();
    String mname = jTextField2.getText();
    String lname = jTextField3.getText();

    String lineone = jTextField4.getText();
    String linetwo = jTextField5.getText();
    String linethree = jTextField6.getText();

    int fnam = fname.length();
    int mnam = mname.length();
    int lnam = lname.length();
    int lineon = lineone.length();
    int linetw = linetwo.length();
    int linethre = linethree.length();

    int[] check = {fnam, mnam, lnam, lineon, linetw, linethre};
    for (int i = 0; i < check.length; i++) {
        if (check[i] == 0) {
            //needs to show which jTextfield/s is/are empty and make their backgrounds RED
        } else {
            //save to database----> I know what I have to do here.
        }
    }
}

Thank you very much :)This is my Application

Answer 1

For that you need to add change listener (a DocumentListener which reacts for change in the text) for your JTextField, and within actionPerformed(), you need to update the loginButton to enabled/disabled depending on the whether the JTextfield is empty or not.

You can add action listener to know does your textfield has changed, or not.

yourJTextField.getDocument().addDocumentListener(new DocumentListener() {
  public void changedUpdate(DocumentEvent e) {
    changed();
  }
  public void removeUpdate(DocumentEvent e) {
    changed();
  }
  public void insertUpdate(DocumentEvent e) {
    changed();
  }

  public void changed() {
     if (yourJTextField.getText().equals("")){
       loginButton.setEnabled(false);
     }
     else {
       loginButton.setEnabled(true);
    }

  }
});

Then function checkempty would check for flags that could be set in changed(), Example changed() code:

boolean changedField = false;

public static void changed(){
    changedField = true;
}

And check does changedField is true.

Answer 2

Do something like below:

public void checkEmpty() {
    JTextField [] textFields = {jTextField1,jTextField2,jTextField3,jTextField4,jTextField5,jTextField6};
    isInputValid = true;
    for (int i = 0; i < textFields.length; i++) {
        JTextField jTextField = textFields[i];
        String textValue = jTextField.getText().trim();
        if (textValue.length() == 0) {
            //turn background into red
            jTextField.setBackground(Color.RED);
            isInputValid = false;
        }
    }

    // now check if input are valid
    if(!isInputValid) return;

    //save to database----> I know what I have to do here.
}