java - 运行 Java 代码时出错

Question

我正在尝试学习 Java，并创建了一个 GUI 表单，最终看起来像 Yahtzee 评分表。目前，它具有所有字段，但是当我尝试运行它时，出现以下错误:

Exception in thread "main" java.lang.NullPointerException
    at java.awt.Container.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at javax.swing.JFrame.addImpl(Unknown Source)
    at java.awt.Container.add(Unknown Source)
    at Board.<init>(FiveDice.java:97)
    at FiveDice.main(FiveDice.java:9)

想法？

这是我的代码:

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

public class FiveDice {

    public static void main(String[] args)
    {
        new Board();
    } // main
} // FiveDice

class Board extends JFrame {
    private static final long serialVersionUID = 1L;
    private JLabel  l_Ones, l_Twos, l_Threes, l_Fours, l_Fives, l_Sixes, 
                    l_SubtotalT, l_BonusT, l_TotalT;
    private JLabel  l_ThreeKind, l_FourKind, l_FullHouse, l_SmStr8, l_LgStr8, l_FiveDice,
                    l_Chance, l_SubtotalB, l_BonusB, l_GrandTotal;
    private JTextField  Ones, Twos, Threes, Fours, Fives, Sixes,
                        SubtotalT, BonusT, TotalT;
    private JTextField  ThreeKind, FourKind, FullHouse, SmStr8, LgStr8, FiveDice, 
                        Chance, SubtotalB, BonusB, GrandTotal;
    private JButton btnClear;

    public Board() {
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setTitle("Six Dice!!");

        // Labels - Top Section
        l_Ones      = new JLabel("1s: ");
        l_Twos      = new JLabel("2s: ");
        l_Threes    = new JLabel("3s: ");
        l_Fours     = new JLabel("4s: ");
        l_Fives     = new JLabel("5s: ");
        l_Sixes     = new JLabel("6s: ");
        l_SubtotalT = new JLabel("Total: ");
        l_BonusT    = new JLabel("Bonus: ");
        l_TotalT    = new JLabel("Grand Total: ");

    // Input Fields - Top Section
        Ones        = new JTextField(2);
        Twos        = new JTextField(2);
        Threes      = new JTextField(2);
        Fours       = new JTextField(2);
        Fives       = new JTextField(2);
        Sixes       = new JTextField(2);
        SubtotalT   = new JTextField(3);
        BonusT      = new JTextField(3);
        TotalT      = new JTextField(3);

        // Labels - Bottom Section
        l_ThreeKind     = new JLabel("3 of a Kind: ");
        l_FourKind      = new JLabel("4 of a Kind: ");
        l_FullHouse     = new JLabel("Full House: ");
        l_SmStr8        = new JLabel("Sm. Straight: ");
        l_LgStr8        = new JLabel("Lg. Straight: ");
        l_FiveDice      = new JLabel("Five Dice: ");
        l_Chance        = new JLabel("Chance: ");
        l_SubtotalB     = new JLabel("Total: ");
        l_BonusB        = new JLabel("Bonus: ");
        l_GrandTotal    = new JLabel("Grand Total: ");

    // Input Fields - Bottom Section
        ThreeKind   = new JTextField(2);
        FourKind    = new JTextField(2);
        FullHouse   = new JTextField(2);
        SmStr8      = new JTextField(2);
        LgStr8      = new JTextField(2);
        FiveDice    = new JTextField(2);
        Chance      = new JTextField(2);
        SubtotalB   = new JTextField(3);
        BonusT      = new JTextField(3);
        GrandTotal  = new JTextField(3);

        // Add to Frame - Top Section
        add(l_Ones);        add(Ones);
        add(l_Twos);        add(Twos);
        add(l_Threes);      add(Threes);
        add(l_Fours);       add(Fours);
        add(l_Fives);       add(Fives);
        add(l_Sixes);       add(Sixes);
        add(l_SubtotalT);   add(SubtotalT);
        add(l_BonusT);      add(BonusT);
        add(l_TotalT);      add(TotalT);

        // Add to Frame - Bottom Section
        add(l_ThreeKind);   add(ThreeKind);
        add(l_FourKind);    add(FourKind);
        add(l_FullHouse);   add(FullHouse);
        add(l_SmStr8);      add(SmStr8);
        add(l_LgStr8);      add(LgStr8);
        add(l_FiveDice);    add(FiveDice);
        add(l_Chance);      add(Chance);
        add(l_SubtotalB);
        add(SubtotalB);
        add(l_BonusB);
        add(BonusB);
        add(l_GrandTotal);
        add(GrandTotal);

        // Buttons
        btnClear = new JButton( "Clear" );
        btnClear.addActionListener(
            new ActionListener()
            {
                public void actionPerformed( ActionEvent e )
                {
                    clear();
                }
            }); add( btnClear );

        setLayout( new FlowLayout() ); // Choose a layout
        pack(); // Get rid of extra space
        setLocationRelativeTo(null); // Centers the window
        setVisible(true);
  } // Board Method

    private void clear() {
        Ones.setText( "" );
        Twos.setText( "" );
        Threes.setText( "" );
        Fours.setText( "" );
        Fives.setText( "" );
        Sixes.setText( "" );
        SubtotalT.setText( "" );
        BonusT.setText( "" );
        TotalT.setText( "" );
        ThreeKind.setText( "" );
        FourKind.setText( "" );
        FullHouse.setText( "" );
        SmStr8.setText( "" );
        LgStr8.setText( "" );
        FiveDice.setText( "" );
        Chance.setText( "" );
        SubtotalB.setText( "" );
        BonusB.setText( "" );
        GrandTotal.setText( "" );
    } // clear
} // Board Class

Answer 1

第 97 行是你的问题。 BonusB 为空，因此您无法添加它:

add(BonusB);