question about java.lang.NullPointerException


  • 0
    V

    Hi all,
    When I run my code on the OJ it points out that for the following code I made a null pointer exception.

    int res=head.val;
    

    but isn't the input are guaranteed that the head is not null?
    Can anybody figure out what is happening? I am not familiar with java and appreciate for any help.
    Here attaches all the code.

       ListNode head;
       Random random;
        /** @param head The linked list's head. Note that the head is guanranteed to be not null, so it contains at least one node. */
        public Solution(ListNode head) {
            this.head = head;
            random = new Random();
        }
        
        /** Returns a random node's value. */
        public int getRandom() {
    
            int res=head.val;
          
            for(int count=1;head!=null;count++){
                if(random.nextInt(count)==0)
                    res=head.val;
                    
                head=head.next;
            }
    
            
            return res;
        }
    

  • 0
    C

    same question


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