Question

嘿所有我正在制作航班预订系统并且当我点击预订座位时出现此错误＆＃34; AWT-EventQueue-0＆＃34; java.lang.NullPointerException 我认为我的2D对象初始化存在错误... PS：有没有办法摆脱final

前面的Seats[][] seats = new Seats[4][5];

这是我的座位类：

public class Seats {

private int row_number;
private boolean booked;
private Passenger myPassenger;
private String seat_name;
private String type;
private int column_number;
private long booking_nr;

public Seats(){
    myPassenger = new Passenger();
    booked = false;
}

public boolean isBooked() {
    return booked;
}

public void setBooked(boolean booked) {
    this.booked = booked;
}

}

以下是我的GUI：

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.EventQueue;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;

public class Book_GUI extends JFrame {

//private EconomyClass eco;
private JPanel contentPane;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                Book_GUI frame = new Book_GUI();
                frame.setTitle("Economy Class");
                frame.setVisible(true);

            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the frame.
 */
public Book_GUI() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);

    int left = 3;
    int middle = 3;
    int right = 4;

    String[] singleRowAll = new String [left+middle+right];

    for(int i = 1;i<singleRowAll.length;i++){singleRowAll[i] = "";}
    singleRowAll[0] = "Window";
    singleRowAll[left-1] = "Aisle";
    singleRowAll[left] = "Aisle";
    singleRowAll[left+middle-1] = "Aisle";
    singleRowAll[left+middle] = "Aisle";
    singleRowAll[left+middle+right-1] = "Window";


    //eco = new EconomyClass(4,5,3,3,4);

    final Seats[][] seats = new Seats[4][10];
    for ( int i = 0; i < 4; i++) {
        char c= 'A';
        for ( int j = 0; j < 10; j++) {
            final int x = i;
            final int z = j;
        final JButton btnBookFlight = new JButton(" " + (i+1) + c++ + " " + singleRowAll[j] );
            btnBookFlight.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {
                    if(seats[x][z].isBooked()){btnBookFlight.setBackground(Color.GREEN);}

                    seats[x][z].setBooked(true);

                    //JButton button = (JButton)arg0.getSource();
                    //button.setBackground(Color.RED);
                //  btnBookFlight.setBackground(Color.RED);
                    btnBookFlight.setOpaque(true);
                }
            });
            contentPane.add(btnBookFlight);
        }
    }

    contentPane.setLayout(new GridLayout(4, 10));
    pack();
}

}

感谢您的阅读和时间！

Answer 1

您正在使用new Seats[4][5]创建一个新的座位数组，但这只是一个空的引用数组。你需要在数组中的每个位置创建一个新的座位。

Answer 2

您没有初始化Seats [] []数组。尝试使用：

替换Book_GUI.java的构造函数

public Seats[][] seats = new Seats[4][10]; 

public Book_GUI() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    contentPane = new JPanel();
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);

    int left = 3;
    int middle = 3;
    int right = 4;

    String[] singleRowAll = new String[left + middle + right];

    for (int i = 1; i < singleRowAll.length; i++) {
        singleRowAll[i] = "";
    }
    singleRowAll[0] = "Window";
    singleRowAll[left - 1] = "Aisle";
    singleRowAll[left] = "Aisle";
    singleRowAll[left + middle - 1] = "Aisle";
    singleRowAll[left + middle] = "Aisle";
    singleRowAll[left + middle + right - 1] = "Window";

    // eco = new EconomyClass(4,5,3,3,4);

            //Delete this line:
    //final Seats[][] seats = new Seats[4][5];

    for(int i = 0; i < 4; i++) {
        for(int j = 0; j < 5; j++) {
            seats[i][j] = new Seats();
        }
    }

    for (int i = 0; i < 4; i++) {
        char c = 'A';
        for (int j = 0; j < 10; j++) {
            final int x = i;
            final int z = j;
            final JButton btnBookFlight = new JButton(" " + (i + 1) + c++
                    + " " + singleRowAll[j]);
            btnBookFlight.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {
                    if (seats[x][z].isBooked()) {
                        btnBookFlight.setBackground(Color.GREEN);
                    }

                    seats[x][z].setBooked(true);

                    // JButton button = (JButton)arg0.getSource();
                    // button.setBackground(Color.RED);
                    // btnBookFlight.setBackground(Color.RED);
                    btnBookFlight.setOpaque(true);
                }
            });
            contentPane.add(btnBookFlight);
        }
    }

    contentPane.setLayout(new GridLayout(4, 10));
    pack();
}

这应该有帮助：）

“AWT-EventQueue-0”java.lang中的NullPointerException

2 个答案: