Question

public class Depot extends Item2
{
}

public class Ship extends Item2
{
}

abstract public class Item2
{
    public static void loadFromStream(FileInputStream oos) throws IOException
    {
        return new whatToWriteHereToGetDEPOTorSHIP?
    }
}

Depot o1 = Depot.loadFromStream(oos);
Ship o2 = Ship.loadFromStream(oos);

代码中的问题：如何从静态方法创建Ship或Depot的实例？根据仓库。或发货。

Answer 1

abstract public class Item2 {
    public static Item2 loadFromStream(FileInputStream oos) throws IOException {
        try (ObjectInputStream ois = new ObjectInputStream(oos)) {
            return (Item2) ois.readObject();
        }
    }
}

之后你需要施展。如果您想要描述静态调用，请在子类中创建它们：

public class Depot extends Item2 {
    static Depot loadDepotFromStream(FileInputStream oos) {
         return (Depot)loadFromStream(oos);
    }
}

Answer 2

你可以这样做：

public class Depot extends Item2
{
    public static Depot loadFromStream(FileInputStream oos) throws IOException
    {
        return Item2.loadFromStream(oos, Depot::new);
    }
}

public class Ship extends Item2
{
    // ... similar here
}

abstract public class Item2
{
    protected static <T extends Item2> T // notice the "protected"
            loadFromStream(FileInputStream oos, Supplier<T> cons) throws IOException
    {
        T t = cons.get()
        // ...common logic...
        return t;
    }
}

Answer 3

如果不传递有关要创建的类的信息作为参数，则无法执行此操作。

编译器处理以下2个相同的调用

Depot.loadFromStream(oos);
Ship.loadFromStream(oos);

这个电话

Item2.loadFromStream(oos);

请注意FileInputStream可以存储有关该对象的信息。在这种情况下，您需要根据此信息处理对象创建...（有些类在标准API中为您执行此操作。）

Answer 4

你可以这样做......

package main;

import java.io.FileInputStream;
import java.io.IOException;

public class Exam {
    public static void main(String[] args) throws Throwable {

        Depot depot = (Depot)Depot.loadFromStream(null, Depot.class);
        System.out.println(depot);
        Ship ship = (Ship)Ship.loadFromStream(null, Ship.class);
        System.out.println(ship);

    }
}

class Depot extends Item2
{
}

class Ship extends Item2
{
}

abstract class Item2
{
    public static Object loadFromStream(FileInputStream oos, Class c) throws IOException, Throwable
    {   
        return c.newInstance();
    }
}

Java，静态方法可以实例化一个被调用的对象吗？

4 个答案: