Question

所以，我正在飞机上创建一系列座位，其特征是座位数，座位类型和乘客。

首先，我的代码将座位对象放在一个单独的类中：

public class Seat {

private int seatNumber;
private String passenger;
private String seatType;

public Seat(int seatNumber, String seatType, String passenger){
    seatNumber=this.seatNumber;
    seatType=this.seatType;
    passenger=this.passenger;
}
public int getSeatNumber() {
    return seatNumber;
}

public String getPassenger() {
    return passenger;
}

public String getSeatType() {
    return seatType;
}

在我的主要课程中，我有：

    import javax.swing.*;

    import java.awt.*;
    import java.awt.List;
    import java.util.*;

    public class AirplaneReservation {
public static Seat []seatList= new Seat[12];


public void SeatList(){
    for (int i=0; i<seatList.length; i++){
        seatList[i]= new Seat(i, null, null);
    }

    Seat seat1 = new Seat(1, "First Class", "Collins");
    seatList[0]=seat1;
    Seat seat2 = new Seat(2, "First Class", "null");
    seatList[1]=seat2;
    Seat seat3 = new Seat(3, "First Class", "Faivre");
    seatList[2]=seat3;
    Seat seat4 = new Seat(4, "First Class", "Kinnard");
    seatList[3]=seat4;;
    Seat seat5 = new Seat(5, "Coach", "null");
    seatList[4]=seat5;
    Seat seat6 = new Seat(6, "Coach", "null");
    seatList[5]=seat6;
    Seat seat7 = new Seat(7, "Coach", "Morgans");
    seatList[6]=seat7;
    Seat seat8 = new Seat(8, "Coach", "Rohan");
    seatList[7]=seat8;
    Seat seat9 = new Seat(9, "Coach", "Shatrov");
    seatList[8]=seat9;
    Seat seat10 = new Seat(10, "Coach", "Sword");
    seatList[9]=seat10;
    Seat seat11 = new Seat(11, "Coach", "null");
    seatList[10]=seat11;
    Seat seat12 = new Seat(12, "Coach", "Tuckness");
    seatList[11]=seat12;
}

public static void main (String [] args){

    System.out.println("Seat\tPassenger");
    System.out.println(seatList[0].getSeatNumber());

我发现很多人都遇到了不使用非null对象创建数组的问题，但是当我尝试使用我认为的代码块时，我仍然会得到一个空指针异常。

Exception in thread "main" java.lang.NullPointerException
    at AirplaneReservation.main(AirplaneReservation.java:45)

如果不将这些对象设为null，我缺少什么？

Answer 1

你的main（）方法正在访问尚未填充的静态seatList字段（尚未调用SeatList（））。

seatList应该是非静态的，并且可以通过getter方法访问，以强制该对象在使用之前完全初始化。

或使SeatList（）静态并从静态初始值设定项中调用它以确保它被调用。

Answer 2

这是一个空指针异常，因为你忘了调用函数将Seats添加到数组中。就像现在一样，你定义了一个Seats数组，但没有添加任何东西，所以默认情况下，一切都是null。

请记住在main方法中调用SeatList（）。

我在对象数组中得到空指针异常

2 个答案: