创建自己的toString方法后丢失了java对象标识

Question

assume I have my own linkedlist implementation:

class ListNode {
    int val;
    ListNode next;

    ListNode(int x) {
        val = x;
    }
}

When I have this simple setup, I can use a node in a Map:

ListNode A = new ListNode(1);
ListNode B = new ListNode(2);
ListNode C = new ListNode(3);
A.next = B;
B.next = C;

Map<ListNode, Integer> hmp = new HashMap<>(Map.ofEntries(
    Map.entry(A, 1)
));

When I print the Map object, I got:

System.out.println(hmp);
// >>> {ListNode@57829d67=1}

However, after I implement a toString method for my linkedlist, so that I can print it out straightforwardly:

public String toString() {
    if (this.next != null) {
        return this.val + "->" + this.next.showString();
    } else {
        return String.valueOf(A.val);
    }
}

Now If I can print the linked list nicely, but if I print the Map again:

System.out.println(A);
// >>> 1->2->3
System.out.println(hmp);
// >>> {1->2->3=1}

You can see that I lost the original way of showing the identity of the ListNode object in map.

1. Is there any way to fix this?
2. Is there a method that I can call to ListNode to show ListNode@57829d67 ?

The only that I can see is not to override the toString method but create a different method to show the string of my linkedlist object. I am not sure if this is a good idea

Thanks

Answer 1

That is not an "identity"; it is the hashCode() of your ListNode . Call hashCode() to get the "57829d67" whenever you want.