Question

I have tried every possible question here, but couldnt get around it.

I have a java file(android activity) where I declare

private someAdapter someAdapterObj;

Inside onCreate() I call the constructor and get the adapter is instantiated.

this.someAdapterObj= new someAdapter (this,
                       R.layout.item_row,someAdapter.getAllNews());

Inside someAdapter file, I have

private static someArrayList;

I also have a addtoarraylist() inside someAdapter.

Now, I call the addtoarraylist() from onCreate in the mainActivity, but before I instantiate the adapter. This should be possible because, the arraylist is static. But, I get a nullpointer exception when i add to the arraylist. Can someone please help me?

Answer 1

Any instance or static variable whose type is a class (not a primitive) defaults to null. You need to initialize it – for example:

private static List<Foo> someArrayList = new ArrayList<Foo>();

However:

• ArrayList is not thread-safe, so you’ll need synchronization
• The use of static variables like this is a bit of a code smell (global state); it’s usually cleaner if you can hook your components up appropriately so you don’t need any global state