内部类的Java方法调用与外部类的输出不同

Question

I am making a Tic-Tac-Toe computer and I need to know when the current letter is O so the computer can make its move. However, from the main method, the current letter always looks like O , but from inside the GUI class the current letter changes as it should.

Here is the GUI class: I tried to only include the relevant methods.

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Arrays;

import javax.swing.JButton;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class TicGUI extends JPanel {    
    private JButton btns[] = new JButton[9];
    private String xnos[] = new String[9];
    private String currentLetter = "X";

    public TicGUI() {
        initBtns();
        initBoard();
    }

    public String getCurrentLetter() {
        return currentLetter;
    }

    public void initBtns() {
        for(int i = 0; i < 9; i++) {
            btns[i] = new JButton();
            btns[i].addActionListener(new TicListener());
        }
    }

    public void initBoard() {
        this.setLayout(new GridLayout(3, 3));
        for(int i = 0; i < btns.length; i++) {
            this.add(btns[i]);
        }
    }

    private class TicListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent e) {
            JButton btn = (JButton) e.getSource();
            if(btn.getText().equals("") && btn.isEnabled()){
                btn.setText(currentLetter);
                btn.setEnabled(false);
                if(currentLetter.equals("X"))
                    currentLetter = "O";
                else
                    currentLetter = "X";
                System.out.println("In class:" + getCurrentLetter());
            }
        }
    }
}

Here is the class with the main method:

import java.util.Scanner;

import javax.swing.JFrame;

public class TICTICTIC {

    public static void main(String[] args) {
        TicGUI tic = new TicGUI();
        JFrame frame = new JFrame("t");
        frame.add(new TicGUI());
        frame.setSize(500, 500);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        Scanner scan = new Scanner(System.in);
        while(true) {
            String ans = scan.nextLine();
            System.out.println(tic.getCurrentLetter());
        }
    }
}

My expected output would be:

In main: X         // <- pressed enter
In GUI class: O    // <- clicked a button, made currentLetter change

In main: O         // <- pressed enter
In GUI class: X    // <- clicked a button, made currentLetter change

In main: X         // <- you get the idea
In GUI class: O    

In main: O

The "In main" letter alternates along with the GUI class output.

Instead I get:

In main: X
In GUI class: O

In main: X
In GUI class: X

In main: X
In GUI class: O

In main: X

The "In main" output stays the same the whole time. Why?

Answer 1

You're creating two instances of TicGUI ...

TicGUI tic = new TicGUI();
JFrame frame = new JFrame("t");
frame.add(new TicGUI());

One is getting added to the GUI the other you are trying to extract the value from, each has it's own value of currentLetter