Question

我制作了这个程序，它处理类和关系，当我运行它时，它给出了错误“线程中的异常”主“java.lang.NullPointerException”，我的IDE没有检测到编码中的任何错误，任何人都可以帮助我，这非常烦人。

import java.util.Vector;
class Flight {
    private String id;
    private String destination;
    private Time depart;
    private Time arrival;
    private Vector passengerList;
    public Flight(String a, String b, Time c, Time d) {
        id = a;
        destination = b;
        depart = c;
        arrival = d;
    }
    public void addPassenger(Passenger a) {
        passengerList.add(a);
    }
    public void printInfo() {
        System.out.println("Id " + id);
        System.out.println("Destination " + destination);
        System.out.println("Depart " + depart.getHour() + " " + depart.getMinute());
        System.out.println("Arrival " + arrival.getHour() + " " + arrival.getMinute());
        System.out.println("Number of passengers " + passengerList.size());
    }
}
class Time {
    private int hour;
    private int minute;
    public Time(int a, int b) {
        hour = a;
        minute = b;
    }
    public int getHour() {
        return hour;
    }
    public int getMinute() {
        return minute;
    }
}
class Passenger {
    private String name;
    private int age;
    public Passenger(String a, int b) {
        name = a;
        age = b;
    }
}
class FlightTester {
    public static void main(String[] args) {
        Time dep = new Time(8, 10);
        Time arr = new Time(9, 00);
        Flight f = new Flight("PK-303", "Lahore", dep, arr);
        Passenger psg1 = new Passenger("Umair", 30);
        Passenger psg2 = new Passenger("Manzoor", 44);
        f.addPassenger(psg1);
        f.addPassenger(psg2);
        f.printInfo();
    }
}

Answer 1

private Vector passengerList;

未初始化，可能是问题。

Answer 2

    Vector passengerList are not initialized.

致电

    f.addPassenger(psg2);

你会得到NullPointException。

使用List会比vector

更好

Answer 3

private Vector passengerList;

你永远不会初始化它，所以当你的代码遇到任何引用passengerList的东西时，你会得到一个空指针异常。

奇怪的运行时错误

3 个答案: