如何设置/获取名称 "ford" - 我在 class Vehicle 的主要方法中创建的 class Car 的实例？

Question

如您所见，我卡在了应该为福特所有者设置名称的部分...感谢您的帮助。

public class Vehicle {

    Person owner;
    long motorSerialNo;
    String registerNo;

    public static void main(String[] args) {

        //an example, create an object instance of class Car

        Car ford           = new Car();
        ford.model         = "Focus";
        ford.motorSerialNo = 123456;
        ford.registerNo    = "CA-126-65";

        //and here is a problem

        ford.owner.setName("John Croul");


    }

}

class Car extends Vehicle {

    String model;

}

class Person {

    public Person(String name){
        this.name = name;
    }
    String name;
    String lastname;
    String address;

    String getName() {
        return name;
    }

    void setName() {
        this.name = name;
    }
}

Answer 1

首先，您的 setter 应该看起来像

public void setName(String name) {
    this.name = name;
}

然后你必须在调用它的方法setName()之前初始化实例变量person，否则你会得到NullPoiterException.

Person owner = new Person();

或在 main 方法中，就像您对其他变量所做的那样

ford.owner = new Person();

如何设置/获取名称 "ford" - 我在 class Vehicle 的主要方法中创建的 class Car 的实例？

How to set / get a name to "ford" - instance of class Car I have created in main method of class Vehicle?

java

setter

initialization

instance-variables