having a field with the same class inside a class

Question

Consider this following example

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

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

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 ?

Answer 1

What is the point of having a h1 in there ?

That would depend entirely on the class.

How can it be used ?

Like any other instance member.

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

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...
}

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.

---

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...
}

Answer 2

One of the example, If you have a tree like structure then a node can contain child of its own type. That is the reason your Human class has an attribute of its own type.