在一个班级中有一个具有相同班级的字段 [英] having a field with the same class inside a class

问题描述

考虑以下示例

public class Human
{
public Human h1;
public String name;
public int age;

public Human()
{
  name = "myName";
      age = 22;
}
}

在其中拥有h1有什么意义？如何使用？以及为什么要使用它？
我们不能只使用将用新的实例创建的实例吗？

What is the point of having a h1 in there ? How can it be used ? and why would it be used ? Can't we just use the instance that we would create with the new ?

推荐答案

在其中有h1的意义是什么？

What is the point of having a h1 in there ?

这完全取决于类。

如何使用？

How can it be used ?

像其他任何实例成员一样

Like any other instance member.

为什么要使用它？我们不能只使用将用新的实例创建的实例吗？

and why would it be used ? Can't we just use the instance that we would create with the new ?

考虑一个链表，其中每个节点都有链接下一个（可能是上一个）节点。这些链接与节点本身属于同一类。例如，大致：

Consider a linked list, where each node has links to the next (and possibly previous) nodes. Those links would be the same class as the node itself. E.g., roughly:

class LinkedListNode {
    private LinkedListNode previous;
    private LinkedListNode next;
    private Object value;

    LinkedListNode(LinkedListNode p, LinkedListNode n, Object v) {
        this.previous = p;
        this.next = n;
        this.value = v;
    }

    LinkedListNode getPrevious() {
        return this.previous;
    }

    // ...and so on...
}

还有许多其他类似的用例。 人班级可能有关联人员（配偶，孩子）的成员。一个树类可能有叶子，而叶子可能有到其他叶子的链接。等等。

There are lots of other similar use cases. A Person class might have members for associated persons (spouses, children). A tree class probably would have leaves, which would probably have links to other leaves. Etc.

在评论中，您询问了单例课程。是的，绝对是在这种情况下，您会有一个属于此类的成员。这是一个标准的单例（此主题有很多变体）：

In the comments, you asked about a singleton class. Yes, that's absolutely a case where you'd have a member that was the type of the class. Here's a standard singleton (there are many variations on this theme):

class Foo {
    // The singleton instance
    static Foo theInstance = null;

    // Private constructor
    private Foo() {
    }

    // Public accessor for the one instance
    public static synchronized Foo getInstance() {
        if (theInstance == null) {
            theInstance = new Foo();
        }
        return theInstance;
    }

    // ...stuff for Foo to do, usually instance methods...
}

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