How to rectify "over-sensitive" JTextField input issue

I've just come over to JAVA from BASIC, so please forgive me for any convention issues with my coding.

I have a mildly infuritating GUI-related issue. I have constructed a matrix-multiplication calculator which does calculations on inputted letters (using MOD 26). I run the program exclusively on Eclipse and have included a picture of the actual program in operation below...

The issue is with the Jtextfield boxes which take the inputted letters:

Actual program running on Eclipse

Basically, I wanted to be able to input a letter in a box, then to have the cursor move to the next box (cycling back to the first box after all the letters are inputted). I used a 'KeyListener' as shown in the code for the first JTextField 'letter box':

  A_RUCE = new JTextField(2);
  A_RUCE.setFont(new Font("Serif", Font.PLAIN, 18));
  A_RUCE.setEditable(true);
  cp.add(A_RUCE);
  A_RUCE.setText("");
  
  A_RUCE.addKeyListener(new KeyAdapter(){
      public void keyPressed(KeyEvent e){
      String value=A_RUCE.getText();
      if(value.length()==0){
          B_RUCE.requestFocus();
      }
    }
  });

The problem is that when I run the program, most of the time, the thing becomes "over sensitive". I try to input a letter and the cursor skips a box. I consider key repeating rate on my computer and such, and have adjusted settings, but this did not help.

All I am seeking is for when a letter is inputted, that the cursor moves to the next box without it 'skipping' over a box. I don't know why that happens, and I cannot figure out an alternative way to fix the issue. I would be very grateful if someone could help with this. Thank you kindly.

Solution

I'd be more inclined to use a DocumentListener. You can check the length of the text and then move onto the next field. This is the sort of thing you could do:

import java.awt.Component;
import java.awt.Container;
import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JPanel;
import java.awt.EventQueue;
import javax.swing.event.DocumentListener;
import javax.swing.event.DocumentEvent;

public class FB extends JFrame implements DocumentListener {
    private JTextField[] fields = new JTextField[3];

    public void insertUpdate(DocumentEvent e) {
        int textLen = e.getDocument().getLength();
        if (textLen == 1) {
            // focus next
            int nextToFocus = 0;
            Component c = getFocusOwner();
            for (int i = 0; i < fields.length; i++) {
                if (fields[i] == c) {
                    nextToFocus = i + 1;
                    break;
                }
            }
            nextToFocus %= fields.length;
            System.out.printf("Next to focus is field %d%n", nextToFocus);
            fields[nextToFocus].requestFocus();
        }
    }

    public void removeUpdate(DocumentEvent e) {
    } // No-op

    public void changedUpdate(DocumentEvent e) {
        // No-op
    }

    private void setGui() {
        try {
            setLocation(0, 100);
            setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            Container cp = getContentPane();
            JPanel fieldsPanel = new JPanel();
            for (int i = 0; i < fields.length; i++) {
                JTextField tf = new JTextField(1);
                tf.getDocument().addDocumentListener(this);
                fieldsPanel.add(tf);
                fields[i] = tf;
            }
            setContentPane(fieldsPanel);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        try {
            EventQueue.invokeAndWait(() -> {
                FB f = new FB();
                f.setGui();
                f.setSize(200, 200);
                f.setVisible(true);
            });
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}