有没有大佬给看下这个代码哪里有问题。不管运行什么，都显示“ERROR” 
package MYM;

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class MYM {

    // Declare frame, text field and buttons
    private JFrame frame;
    private JTextField textField;
    private String currentInput = "";

    // Constructor to setup GUI components
    public MYM() {
        // Create frame
        frame = new JFrame("Calc...