LinkedList add() append null instead of value 15

Asked Oct 10 '20 at 15:24

Active Oct 10 '20 at 16:19

Viewed 31 times

Using LinkedList to populate a stack of Long type elements. For some reason, value null is added instead of 15 when I call my push method. Why is that?

import java.util.LinkedList;

public class LongStack {

   public static void main (String[] argum) {
      LongStack s = new LongStack();
      s.push(15);
      System.out.println(s);
   }
   
   private LinkedList<Long> l;

   LongStack() {
      l = new LinkedList<Long>();
   }

   public void push (long a) {
      l.add(a);
   }

OK, i found the problem. My bad. There was an overriding toString method (return null;) later in my code that wasn't implemented. But thanks for the tips.

edited Oct 10 '20 at 16:19

asked Oct 10 '20 at 15:24

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Where do you see null is added ? Your code works – azro Oct 10 '20 at 15:28
2

Don't name all of your variables `l`. That makes it hard to determine which `l` is being operated on. – Elliott Frisch Oct 10 '20 at 15:29
I can't reproduce the behaviour you describe. The code works. I only had to change how the linkedlist is printed because simply feeding it to a `System.out.println()` didn't print its contents. – JustAnotherDeveloper Oct 10 '20 at 15:29
https://pastebin.pl/view/ef437ecf – azro Oct 10 '20 at 15:31
1

LinkedList is a generic typed class so it should be created as `LinkedList` assuming the type you want is `long`. – WJS Oct 10 '20 at 15:31

LinkedList add() append null instead of value 15

0 Answers0