使用KeyListener來使用setText時發生NullPointerException

Question

這是一個猜詞游戲。 每次都會顯示第一個字母，而其余的則不會顯示。 每當用戶鍵入我想要它更改板上的字母時，以下是屏幕截圖： http : //puu.sh/7moQS.jpg

錯誤：

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at BoardUI.keyTyped(BoardUI.java:48)

行BoardUI.java:48在哪里

b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setText(typed + "");

Game.java

public class Game {
}

testGUI.java

public class testGUI {
public static void main(String[] args) {
    new GUI("Lingo");
}
}

BoardUI.java

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

public class BoardUI extends JPanel implements KeyListener {

private final Game game;
private Board b = new Board();
private Color hoverColor = new  Color(100, 100, 255);

public BoardUI(LayoutManager layout, Game game, String word) {
    super(layout);
    this.b = new Board();
    this.game = game;
    initComponents(word);
}

public BoardUI(Game game) {
    this.game = game;
}

private void initComponents(String word) {
    this.setLayout(new GridLayout(5, 5, 2, 2));
    for (int i = 0; i < 5 * 5; i++) {
        b.getLetters()[i] = new Label();
        b.getLetters()[i].setBackground(Color.WHITE);
        b.getLetters()[i].setForeground(Color.BLACK);
        b.getLetters()[i].setAlignment(Label.CENTER);
        b.getLetters()[i].setFont(new Font("Big", Font.BOLD, 48));
        this.add(b.getLetters()[i]);
    }

        for (int i = 0; i < 5; i++) {
            b.getLetters()[i].setText(word.charAt(i) + "");
            b.getLetters()[i].setBackground(Color.BLUE);
        }
    b.setCurrentColumn(0);
    b.setCurrentRow(0);
    }

@Override
public void keyTyped(KeyEvent e) {
    char typed = e.getKeyChar();

    if (Character.isLetter(typed) && b.getCurrentColumn() < 5) {
        typed = Character.toUpperCase(typed);
        b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setText(typed + "");
        b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setBackground(Color.BLUE);

        if (b.getCurrentColumn() == 0) {
            for (int i = 1; i < 5; i++) {
                b.getLetters()[b.position(b.getCurrentRow(), i)].setText(".");
                b.getLetters()[b.position(b.getCurrentRow(), i)].setBackground(Color.BLUE);
            }

            b.nextColumn(true);

            if (b.getCurrentColumn() < 5) {
                b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setBackground(hoverColor);
            }

            if (typed == 8 && b.getCurrentColumn() >= 0) {
                this.oneBack();
            }
        }
    }
}

private void oneBack() {
    if (b.getCurrentColumn() < 5) {
        b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setBackground(Color.BLUE);
        b.nextColumn(false);
        b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setText(".");
        b.getLetters()[b.position(b.getCurrentRow(), b.getCurrentColumn())].setBackground(Color.BLUE);
    }
}

@Override
public void keyPressed(KeyEvent e) {

}

@Override
public void keyReleased(KeyEvent e) {

}
}

Board.java：

import java.awt.*;

public class Board {
private Reader reader = new Reader();
private Label[] letters = new Label[5 * 5];
private String[] words = new String[100];
private int currentRow, currentColumn;

public Label[] getLetters() {
    return letters;
}

public String firstWord() {
    return getWord().charAt(0) + "....";
}

public String getWord() {
    int count = reader.LeesWoordenVanFile(words);
    int x = (int) (Math.random() * 100);
    int gokX = (x % count);
    return words[gokX].toUpperCase();
}

public int position(int row, int column) {
    return row * 5 + column;
}

public void nextColumn(boolean next) {
    if (next) {
        currentColumn++;
    } else {
        currentColumn--;
    }
}

public int getCurrentRow() {
    return currentRow;
}

public int getCurrentColumn() {
    return currentColumn;
}

public void setCurrentRow(int currentRow) {
    this.currentRow = currentRow;
}

public void setCurrentColumn(int currentColumn) {
    this.currentColumn = currentColumn;
}
}

GUI.java：

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

public class GUI extends JFrame {

private JPanel gamePanel;
private Game game;
private Board board = new Board();
private BoardUI boardUI = new BoardUI(game);

public GUI(String title) throws HeadlessException  {
    super(title);
    game = new Game();
    setupVieuw();
    showFrame();
    this.addKeyListener(boardUI);
}

public void setupVieuw() {
    getContentPane().removeAll();
    initComponents(board.firstWord());
    layoutComponents();
    this.validate();
}

public void layoutComponents() {
    getContentPane().add(gamePanel, BorderLayout.CENTER);
}

private void initComponents(String word) {
    gamePanel = new JPanel(new BorderLayout());
    gamePanel.add(new BoardUI(new BorderLayout(),game, word));
}

private void showFrame() {
    this.setBounds(50, 50, 800, 800);
    this.setPreferredSize(new Dimension(600, 600));
    this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    this.pack();
    this.setVisible(true);
    this.doLayout();
}
}

Answer 1

這確實很令人困惑，因為您有一些冗余代碼，並且在某些情況下執行兩次操作，但這就是我的發現。

在GUI.java中，您要在此處實例化BoardUI ：

private Game game;
private Board board = new Board();
private BoardUI boardUI = new BoardUI(game);

請注意，

1. 您正在使用null Game對象初始化BoardUI

2. 您正在調用此BoardUI構造函數：

    public BoardUI(Game game) { this.game = game; } 

   而不是這個構造函數-又名。 一個實際上用new Label()對象填充您的letters數組的對象：

    public BoardUI(LayoutManager layout, Game game, String word) { super(layout); this.b = new Board(); this.game = game; initComponents(word); } 

仍然在GUI.java ，您最終確實調用了另一個initComponents() ，但是使用新的BoardUI實例調用了它。

private void initComponents(String word) {
    gamePanel = new JPanel(new BorderLayout());
    gamePanel.add(new BoardUI(new BorderLayout(),game, word));
}

返回之后，立即返回GUI類構造函數的最后一行，並將鍵偵聽器設置為未運行initComponents()的BoardUI ：

this.addKeyListener(boardUI);

TL; DR：您正在向未運行initComponents()的BoardUI對象添加鍵偵聽器