java - 当单词绝对不为空时获取字符串方法返回空

Question

我正在编写一个刽子手游戏，由于某种原因，我的 getW() 方法在应该返回一个肯定不为 null 的字符串时却返回 null。我广泛添加了 System.out.println 以确保 word 保持不变。除了 getW() 方法之外，其他地方似乎都是相同的，这就是 getW() 返回 null 的原因。

这是我的代码:

Hangman.java:

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

public class Hangman extends JPanel{
    private String word;

    public void setupLayout(JFrame window){
        window.setLayout(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();

        HangmanArea panel1 = new HangmanArea();
        panel1.setBackground(Color.blue);
        c.fill = GridBagConstraints.BOTH;
        c.weightx = 1.0;
        c.weighty = 1.0;
        c.gridx = 0;
        c.gridy = 0;
        window.add(panel1, c);

        GuessedLetters panel2 = new GuessedLetters();
        panel2.setBackground(Color.green);
        c.fill = GridBagConstraints.BOTH;
        c.gridx = 1;
        c.gridy = 0;
        window.add(panel2, c);

        Letters panel3 = new Letters();
        panel3.setBackground(Color.black);
        c.fill = GridBagConstraints.BOTH;
        c.gridx = 0;
        c.gridy = 1;
        c.gridwidth = 2;
        window.add(panel3, c);
        System.out.println("Before repaint: "+ word);
        panel1.callRepaint();
        panel2.callRepaint();
        panel3.callRepaint();
        System.out.println("After repaint: " + word);
    }

    public void startWindow(){
        JFrame window = new JFrame();
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        int screenHeight = (int) screenSize.getHeight();
        int windowHeight = (int) ((screenHeight / 4) * 3);
        window.setSize(windowHeight, windowHeight);
        window.setLocationRelativeTo(null);
        window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setupLayout(window);
        window.setVisible(true);
    }

    public void startGame(){
        Prep prepare = new Prep();
        word = prepare.findWord(true);
        System.out.println("Word found: " + word);
        startWindow();
        System.out.println("Word is unchanged: " + word);
    }

    public static void main(String[] args){
        Hangman start = new Hangman();
        start.startGame();
    }
    public String getW(){
        System.out.println("getW()'s word: " + word);    //At this point, word is null
        return word;
    }
}

Letters.java:

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;

public class Letters extends JPanel {
    private String word = "aaa";
    public void callRepaint(){
        Hangman object = new Hangman();
        word = object.getW();
        System.out.println("Word for Letters: " + word);
        repaint();
    }
    public void paintComponent(Graphics g){
        super.paintComponent(g);
        g.setColor(Color.white);
        g.drawString("letters", 50, 50);
    }
}

如果这看起来代码很多，我很抱歉，但 Hangman.java 和 Letters.java 是两个重要的类。 Prep.java 的 findWord() 方法只是从单词列表中获取一个随机单词并返回它。我认为没有必要发布该内容，但我可以。除了 callRepaint() 和 paintCompnent(Graphics g) 方法之外，GuessedLetters.java 和 HangmanArea.java 完全是空的。如果您需要，我可以发布它们，但我认为它们不是很重要。

输出可能如下所示:

Word found: night
Before repaint: night
getW()'s word: null
Word for Letters: null
After repaint: night
Word is unchanged: night

我不知道是什么原因造成的。

Answer 1

问题是您没有将已初始化 word 变量的对象(在您发布的示例输出中为“night”)传递给 callRepaint 方法，而是在该方法内创建一个新实例(未连接到您的“主”对象)。相反，您应该将对象作为参数传递，例如:

public void callRepaint(Hangman object){
        word = object.getW();
        System.out.println("Word for Letters: " + word);
        repaint();
}

并在您的 Hangman 类中这样调用它:

panel1.callRepaint(this);
panel2.callRepaint(this);
panel3.callRepaint(this);

或者可能只是传递字符串，例如:

public void callRepaint(String word){
        System.out.println("Word for Letters: " + word);
        repaint();
}

这样调用它:

panel1.callRepaint(getW());
panel2.callRepaint(getW());
panel3.callRepaint(getW());