HashMap field doesn't update

Question

In my java project, I have a private HashMap field (eggs is an enum, bacon is an object that has an ArrayList field). So it's something like:

    class Foo {
       private HashMap<Eggs, Bacon> breakfast;

       foo() {
         this.breakfast = new HashMap<Eggs, Bacon>();}

       void setValues(int x) {
          ArrayList<Integer> temp;
          Bacon b;
          for(int i = 0; i < x; i++) {
             temp.add(i);}
          b = new Bacon(temp);
          this.breakfast.put(Eggs.Scrambled, b);}
    }

Essentially, even if I make sure to call setValues first in my testClass, a call to breakfast.get() or breakfast.size() will always result in a NullPointerException. In my actual code I have several enum to object mappings in for loops. Using the debugger, I found that the values were set but immediately vanished at the end of each loop. I have no idea why my HashMap field isn't saving the values that get put into it. Even when I changed the field to an ArrayList and set or added values, I'd still get the same nullpointer/outofbounds exception

I can post my actual code if needed but I was wondering if anyone had any insight to this. I'm at my wit's end

`foo()` you are trying is Constructor or Method , if Constructor Capitalize it if Method call it before `setValues` — Shantaram Tupe, Oct 07 '16 at 08:05
`this.breakfast.put(Eggs.Scrambled, b);` if your key is Enum value change Hashmap to accept Enum value — Shantaram Tupe, Oct 07 '16 at 08:09

score 0 · Answer 1 · answered Oct 07 '16 at 07:58

You declared ArrayList<Integer> temp without assigning it a value.

List<Integer> temp = new ArrayList<>();

Additionally there are numerous code smells around this, you should try to follow a coding standard (I prefer google's) and try to rethink your design for this; Constructors and probably removing the list entirely would help, but we can't really know without knowing the actual problem/code.

score 0 · Answer 2 · answered Oct 07 '16 at 07:59

you need initialize your ArrayList , thats what is causing the null pointer exception.

Another thing , If you ware using enum as key to a map from my opinion something wrong, HashMap will take decent space, while you have limited keys I do not recommend using Maps, instead you can use an array of Bacon and define an index for each entry in your enum and access the Bacons using it.

HashMap field doesn't update

2 Answers2