java - 使用包含另一个类作为属性的对象的构造函数

Question

我正在尝试测试我的类(class) Location使用另外两个类作为属性 Address和Geolocation但是，当从 main 构造对象时，我收到指针错误。

这就是我的主要部分

import java.util.ArrayList;
public class LocationTest {
    public static void main(String[] args) {

        ArrayList<Location> locationList = new ArrayList<>();
        locationList.add(new Location(new Address(1, "Abubakr rd Almorsalat", "Riyadh", "Saudi Arabia"), new Geolocation(24.7136, 46.6753, 612), 1, "Prince Sultan University"));
        locationList.add(new Location(new Address(1, "Nassria st", "Sfax", "Tunisia"), new Geolocation(34.7478, 10.7662, 20), 2, "Second Location"));
        locationList.get(1).getGeolocation().setAltitude(20);
        locationList.get(0).getAddress().setStreetNumber(15);
        for(Location i : locationList) {
            System.out.println(i.getGeolocation());
        }

    }
}

我在 Location 中使用的两个类都有 getter 和 setter这是他们的设置方法

public void setAddress(Address address) {
    this.address.setStreetNumber(address.getStreetNumber());
    this.address.setStreetName(address.getStreetName());
    this.address.setCity(address.getCity());
    this.address.setCountry(address.getCountry());
}

public void setGeolocation(Geolocation geolocation) {
    this.geolocation.setLatitude(geolocation.getLatitude());
    this.geolocation.setLongitude(geolocation.getLongitude());
    this.geolocation.setAltitude(geolocation.getAltitude());
}

我感觉问题就在这里，但我不确定

错误是

Exception in thread "main" java.lang.NullPointerException
at quiz01.fall2016.Location.setAddress(Location.java:59)
at quiz01.fall2016.Location.<init>(Location.java:20)
at quiz01.fall2016.LocationTest.main(LocationTest.java:13)

构造函数

public Location(Address address, Geolocation geolocation, int id, String name) {
    setAddress(address);
    setGeolocation(geolocation);
    setId(id);
    setName(name);
}

Answer 1

在 setAddress 调用 this.address 上的 setter 之前，请确保正在初始化 this.address。

默认情况下，所有对象都将使用 null 进行初始化，因此您将遇到 NullPointerException。

您的构造函数应如下所示

public Location(Address address, Geolocation geolocation, int id, String name) {
    // Initialize objects.
    this.address = new Address();
    this.geolocation = new Geolocation();
    setAddress(address);
    setGeolocation(geolocation);
    setId(id);
    setName(name);
}