How to reverse a linked list without affecting the original one?

I want to reverse a LinkedList, I wrote the basic program as follows: -

public class ListNode{
    int val;
    ListNode next;
    ListNode(){}
    ListNode(int val){this.val = val;}
    ListNode(int val, ListNode next){this.val = val; this.next = next;}
}

   public ListNode reverseList(ListNode head) {
        ListNode prev = null;
        ListNode curr = head;
        while(curr!=null){
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;  

        }
        return prev;
    }

Here is the program to print the LinkedList

    public void print(ListNode curr){
        while(curr!=null){
            System.out.print(curr.val+" ");
            curr = curr.next;
        }
        System.out.println();
    }

Now my list is [1,2,21]

when I print it output is as follows

1 2 3 1

when I reverse it and print head and reversed the output is as follows: -

ListNode reversed = reverseList(head);
print(head);
print(reversed)

Output

1
1 3 2 1

Can someone explain how to keep head unchanged?

I tried to reverse the linked list. I was successful but after reversing the list , it altered my current list. I want to keep it unchanged.

This sounds like a class project.

Try this:

1. Run the original list and store each value on a stack.
   When you finish the original list the stack (top down) will contain the values
   in reverse order.
2. pop the stack and add the values to a new list.

As @tgdavies already commented, you need to build a new list from scratch.
Walk through the original list from head to tail,
and while walking build the reversed list from tail to head.

public ListNode reverseList(ListNode head) {
   	ListNode reversed = null;
	ListNode curr = head;
	while (curr != null) {
		reversed = new ListNode(curr.val, reversed);
		curr = curr.next;
	}
	return reversed;
}