在泛型类中声明静态泛型变量 [英] Declaring static generic variables in a generic class

问题描述

我读过你不能在泛型类中声明静态变量/方法，我真的不知道如何解决我的问题或解决它，所以我请教你的指导。

我想要的是一个通用的索引，我所有的核心类都会扩展。
我创建了一个游戏引擎，一个例子是，我将拥有不同的游戏状态，这些游戏状态均扩展 State ，然后扩展 Nexus< ;状态> 。我想要静态头部和尾部的原因是，我可以保留所有游戏状态的链接列表，因为它们都是在创建时添加到列表中的。

另一个示例是我将拥有不同的gameobjects，它们都扩展 GameObject ，然后扩展 Nexus< GameObject> 。

这是名为 Nexus 的指数：

 公共抽象类Nexus< T> 
 {
 
 private static T head = null; 
 private static T tail = null; 
 
 private T next = null; 
 private static int num = 0; 
 
保护Nexus（）{this.Add（（T）this）; } 
 
 public T Add（T obj）
（
 
（（Nexus）obj）.next = null; 
 if（num ++ == 0）head = tail = obj; 
 else tail =（tail.next = obj）; 
 
 return obj; 
 
} 
 
} 
  

另一个解决方案或解决方法我都是耳朵！

解决方案

尝试这种方法：定义一个受保护的摘要子类实现的方法，用于为 类类返回一个静态对象。

可能存在一些逻辑问题等，但答案的基础在这里（即编译）：

<编辑：现在授权给HeadAndTail

  / **< T> Nexus * / 
抽象类的一个子类Nexus< T扩展了Nexus< T>> {//这个语法可以让你将T限制在Nexus 
 private T的子类中; 
 
保护Nexus（）{
 this.add（（T）this）; 
 
 $ b $ public T add（T obj）{
 //委托给HeadAndTail 
 return getHeadAndTail（）。add（obj）; 
} 
 
 / ** @return类的静态* / 
 protected abstract HeadAndTail< T> getHeadAndTail（）; 
} 
 
 / **为简化API * / 
类而绑定到一个对象中HeadAndTail< T扩展了Nexus< T>> {
 T head = null; 
 T tail = null; 
 int num = 0; 
 
 public T add（T obj）{
 obj.next = null; 
 if（num ++ == 0）
 head = tail = obj; 
 else 
 tail = tail.next = obj; 
 
 return obj; 
} 
} 
 
类ConcreteNexus扩展了Nexus< ConcreteNexus> {
 //这是静态对象所有实例将从方法返回
 private static HeadAndTail< ConcreteNexus> headAndTail = new HeadAndTail< ConcreteNexus>（）; 
 
保护HeadAndTail< ConcreteNexus> getHeadAndTail（）{
返回headAndTail; //返回静态
} 
} 
  

I've read that you cannot declare static variables/methods inside a generic class and I really have no idea how to solve my problem or work around it so I ask for your guidance.

What I want is a generic "index" that all of my core classes will extend. I'm creating a game-engine and an example is that I will have different gamestates who all extends State who in turn extends Nexus<State>. The reason I want the static head and tail is so that I can keep a linked list of all gamestates since they're all added to that list upon creation.

Another example is that I will have different gameobjects who all extends GameObject who in turn extends Nexus<GameObject>.

This is the index called Nexus:

public abstract class Nexus<T> 
{

    private static T head = null;
    private static T tail = null;

    private T next = null;
    private static int num = 0;

    protected Nexus() { this.Add( (T)this ); }

    public T Add( T obj )
    {

        ((Nexus)obj).next = null;
        if( num++ == 0 ) head = tail = obj;
        else             tail = ( tail.next = obj );

        return obj;

    }

}

If anyone got another solution or a workaround I'm all ears!

解决方案

Try this approach: Define a protected abstract method that subclasses implement to return a static object for their class.

There may be some logic issues etc, but the basics of the answer are here (ie this compiles):

EDITED: Now delegating to HeadAndTail

/** <T> A subclass of Nexus */
abstract class Nexus<T extends Nexus<T>> { // This syntax lets you confine T to a subclass of Nexus
    private T next;

    protected Nexus() {
        this.add((T) this);
    }

    public T add(T obj) {
        // Delegate to HeadAndTail
        return getHeadAndTail().add(obj);
    }

    /** @return a static for the class */
    protected abstract HeadAndTail<T> getHeadAndTail();
}

/** Bundled into one Object for simplicity of API */
class HeadAndTail<T extends Nexus<T>> {
    T head = null;
    T tail = null;
    int num = 0;

    public T add(T obj) {
        obj.next = null;
        if (num++ == 0)
            head = tail = obj;
        else
            tail = tail.next = obj;

        return obj;
    }
}

class ConcreteNexus extends Nexus<ConcreteNexus> {
    // This is the static object all instances will return from the method
    private static HeadAndTail<ConcreteNexus> headAndTail = new HeadAndTail<ConcreteNexus>();

    protected HeadAndTail<ConcreteNexus> getHeadAndTail() {
        return headAndTail; // return the static
    }
}

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