Java :(错误)Main.main(Main.java:14)中线程"main"java.lang.NullPointerException中的异常

Question

我意识到这是一个常见的错误,我已经尝试使用其他有关此确切错误的问题来解决它,但是我无法提出解决方案.我制作了一组10辆车,并设定了每辆车的品牌,颜色和年份.getter和setter方法在另一个名为"Car"的类中.我不确定某些东西设置为null.预先感谢您的任何帮助.

错误:Main.main(Main.java:14)中的线程"main"java.lang.NullPointerException异常

import java.util.Random;

public class Main {

public static void main(String[] args) {

    //Array of 10 cars
    Car[] cars;
    cars = new Car[10];

    //Assign random colors and makes of my choice
    cars[0].setMake("Toyota");
    cars[1].setMake("Kia");
    cars[2].setMake("Porsche");
    cars[3].setMake("Ferrari");
    cars[4].setMake("Honda");
    cars[5].setMake("Jaguar");
    cars[6].setMake("Lexus");
    cars[7].setMake("Nissan");
    cars[8].setMake("BMW");
    cars[9].setMake("Tesla");

    cars[0].setColor("Black");
    cars[1].setColor("Green");
    cars[2].setColor("Silver");
    cars[3].setColor("Red");
    cars[4].setColor("Yellow");
    cars[5].setColor("White");
    cars[6].setColor("Blue");
    cars[7].setColor("Orange");
    cars[8].setColor("Purple");
    cars[9].setColor("Gold");

    //Randomly selected years for the cars
    int maxYear = 2015;
    int minYear = 2010;
    int maxYear2 = 2009;
    int minYear2 = 1990;

    Random r = new Random(1234);
    cars[0].setYear(r.nextInt(maxYear - minYear + 1) + minYear);
    cars[1].setYear(r.nextInt(maxYear - minYear + 1) + minYear);
    cars[2].setYear(r.nextInt(maxYear - minYear + 1) + minYear);
    cars[3].setYear(r.nextInt(maxYear - minYear + 1) + minYear);
    cars[4].setYear(r.nextInt(maxYear - minYear + 1) + minYear);
    cars[5].setYear(r.nextInt(maxYear2 - minYear2 + 1) + minYear2);
    cars[6].setYear(r.nextInt(maxYear2 - minYear2 + 1) + minYear2);
    cars[7].setYear(r.nextInt(maxYear2 - minYear2 + 1) + minYear2);
    cars[8].setYear(r.nextInt(maxYear2 - minYear2 + 1) + minYear2);
    cars[9].setYear(r.nextInt(maxYear2 - minYear2 + 1) + minYear2);

}

}

Answer 1

初始化对象数组不会初始化数组中包含的对象,因此您将获得NullPointerException.

在尝试执行此操作之前:

cars[0].setMake("Toyota");

你应该首先初始化你的Car对象,如下所示:

cars[0] = new Car(); // or use any other appropriate constructor

同样适用于数组中的其他对象.