这两个语句之间到底有什么区别

Question

I am a beginner in java and i was going through this code

    ListNode current = new ListNode();
    current = front;

and

    ListNode current = front;

Arent both set of statements creating a new object or is it that the memory is being reserved only for the first staement andfor the second only a vatriable is getting declared which holds the memory of the fron node?

Answer 1

ListNode current = new ListNode();
current = front;

This creates a new ListNode and assigns it to current . It then immediately overwrites that reference, losing the reference to the new object. This is almost certainly a mistake. The code is equivalent to

new ListNode();
ListNode current = front;

If the ListNode() constructor has no side effects, that first statement is useless, and could just be

ListNode current = front;

Answer 2

The first statement actually creates a new object (which will be garbage collected soon after because current points to another object in the next instruction), whereas the second one only creates a reference to an existing object.

The recommended code is the second one because the ListNode created in the first one is never used so it is useless to instantiate it.