Подключение полей и кнопки - Java

import javax.swing.*;
import java.awt.*;
 
public class Display {
    private JTextField displayField;
 
    public void setDisplayValue(String val) {
        displayField.setText(val);
    }
 
    public String getDisplayValue() {
        return displayField.getText();
    }
 
    public static void main(String[] args) {
        JPanel p1;
 
        JButton button0;
        JPanel windowContent = new JPanel();
        JTextField displayField;

        button0 = new JButton("Enter my pay on display");
        p1 = new JPanel();
 
        JLabel label1 = new JLabel("Enter hours of mouth");
        JTextField field1 = new JTextField(10);
        JLabel label2 = new JLabel("Enter working day in month");
        JTextField field2 = new JTextField(10);
        JLabel label3 = new JLabel("Enter prepayment");
        JTextField field3 = new JTextField(10);
        JLabel label4 = new JLabel("Enter your working time");
        JTextField field4 = new JTextField(10);
        JLabel label5 = new JLabel("Enter your overtime");
        JTextField field5 = new JTextField(10);
        JLabel label6 = new JLabel("Your pay is: ");
        JTextField field6 = new JTextField(10);
 
        windowContent.add(label1);
        windowContent.add(field1);
        windowContent.add(label2);
        windowContent.add(field2);
        windowContent.add(label3);
        windowContent.add(field3);
        windowContent.add(label4);
        windowContent.add(field4);
        windowContent.add(label5);
        windowContent.add(field5);
        windowContent.add(label6);
        windowContent.add(field6);

        p1 = new JPanel();
 
        GridLayout gl = new GridLayout(10, 30);
        p1.setLayout(gl);
 
        windowContent.add(button0);
        CalculatorEngine calcEngine = new CalculatorEngine();
        button0.addActionListener(calcEngine);

        JFrame frame = new JFrame("PAY");
 
        frame.setContentPane(windowContent);
 
        frame.setSize(198, 360);
        frame.setVisible(true);
    }
}