Question

我正在研究java中的游戏，并创建了一个JTextArea来显示大部分文本，以及一个textPrinter方法来将文本追加到JTextArea。但是每当我尝试调用textPrinter时，我都会得到一个空指针异常。我知道传入方法的字符串不是null，因为从textPrinter方法运行System.out.println（text）时它表明值已正确传递。

我的主要课程的相关代码：

public class stickGame {

public JTextArea gameText;
public JPanel gamePanel;
public JFrame gameWindow;

public static void main(String[] args) {
stickGame game = new stickGame();
TextHandler text = new TextHandler();
gameEnabled = true;

while (gameEnabled == true) {

    MainMenu menu = new MainMenu();
    victory = false;

    //SinglePlayer Logic
    if (gameMode == 1) {

        gameLevel = 0;

        while (defeat != true) {

            playerHealth = 100;
            aiHealth = 100 + (25 * gameLevel);
            pRage = 0;
            aiRage = 0 + (10 * gameLevel);
            secondPRage = 0;
            secondPlayerHealth = 100;
            text.textPrinter("Level "+ (gameLevel + 1)+"\n");
                }
            }
        }
    }

我的TextHandler类代码：

import java.util.Scanner;
import java.util.Random;
import java.util.concurrent.TimeUnit;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class TextHandler extends stickGame {

private String pText;

public void WindowHandler() {

    gameWindow = new JFrame("Stick Game");
    gameWindow.setVisible(true);
    gameWindow.setSize(1000, 600);

    gamePanel = new JPanel();
    gamePanel.setMaximumSize(new Dimension(200, 120));
    gamePanel.setVisible(true);

    gameText = new JTextArea();
    gameText.setSize(600, 600);
    gameText.setLineWrap(true);
    gameText.setVisible(true);
    gameText.setFont(new Font("monospaced", Font.PLAIN, 12));

    JButton attackB = new JButton("Attack");
    JButton blockB = new JButton("Block");
    JButton rushB = new JButton("Rush");
    JButton healB = new JButton("Heal");
    JButton ultimateB = new JButton("Ultimate");
    JButton cheatB = new JButton("Cheat");

        attackB.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            playerMoveChoice = "attack";
            duplicateCheck = true;
            }
        });

        blockB.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
                playerMoveChoice = "block";
                duplicateCheck = true;
                }
        });

        rushB.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
                playerMoveChoice = "rush";
                duplicateCheck = true;
                }
        });

        healB.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            playerMoveChoice = "heal";
            duplicateCheck = true;
            }
        });

        ultimateB.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            playerMoveChoice = "ultimate";
            duplicateCheck = true;
            }
        });

        cheatB.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            pRage = stickGame.pRage + 100;
            }
        });

    gamePanel.add(gameText);
    gamePanel.add(attackB);
    gamePanel.add(blockB);
    gamePanel.add(rushB);
    gamePanel.add(healB);
    gamePanel.add(ultimateB);
    gamePanel.add(cheatB);
    gameWindow.add(gamePanel);
    gameWindow.repaint();
 }


 public void textPrinter(String text) {
    System.out.println(text);
    gameText.append(text);
 }
}

这是错误：

Exception in thread "main" java.lang.NullPointerException
    at TextHandler.textPrinter(TextHandler.java:113)
    at stickGame.main(stickGame.java:431)

空指针异常发生在text.textPrinter（＆＃34; Level＆＃34; +（gameLevel + 1）+＆＃34; \ n＆＃34;）;在主要方法。究竟是什么问题，我应该如何解决它？

Answer 1

您的JTextArea是在WindowHandler方法中构造的，永远不会被调用。在构造TextHandler之后调用WindowHandler（）或从TextHandler的构造函数中调用它

JTextArea.append（）方法返回空指针异常

1 个答案: