Java和继承的静态成员 [英] Java and inherited static members

问题描述

假设我有以下类：

class Parent
{
    private int ID;
    private static int curID = 0;

    Parent()
    {
         ID = curID;
         curID++;
    }
}

以及这两个子类：

class Sub1 extends Parent
{
    //...
}

和

class Sub2 extends Parent
{
    //...
}

我的问题是这两个子类从
父类共享相同的静态curID成员，而不是具有不同的。

My problem is that these two subclasses are sharing the same static curID member from parent class, instead of having different ones.

所以，如果我这样做：

{
    Sub1 r1 = new Sub1(), r2 = new Sub1(), r3 = new Sub1();
    Sub2 t1 = new Sub2(), t2 = new Sub2(), t3 = new Sub2();
}

r1，r2，r3的ID将为0,1,2和t1，t2，t3为3,4,5。
而不是这些我希望t1，t2，t3的值为0,1,2，即使用另一个curID静态变量副本。

ID's of r1,r2,r3 will be 0,1,2 and of t1,t2,t3 will be 3,4,5. Instead of these i want t1,t2,t3 to have the values 0,1,2, ie use another copy of curID static variable.

这是可能？如何？

推荐答案

正如其他人已经写过的那样，静态成员绑定到类，所以你需要在类级别跟踪id，例如像这样：

As others already wrote, static members are bound to the class, so you need to track the id on a class level, e.g. like this:

abstract class Parent {
    private int ID;

    Parent() {
         ID = nextId();
    }

    abstract protected int nextId();
}

class Sub1 extends Parent {
    private static int curID = 0;

    protected int nextId() {
       return curID++;
    }

    //...
}

class Sub2 extends Parent {
    private static int curID = 0;

    protected int nextId() {
       return curID++;
    }

    //...
}

<请注意，这种方法不是线程安全的 - 但问题中的代码也不是。您不能从不同的线程同时从同一个子类创建新对象。

Note that this approach is not thread safe - but neither was the code in the question. You must not create new objects from the same sub class concurrently from different threads.

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