CODEWITHSUNDEEP
java
OpenSrcFTW
OpenSrcFTW

Reputation: 211

I don't understand this NullPointerException

I have the following code:

RoomCell r = b.GetRoomCellAt(1, 2);
assertTrue(r.isDoorway());

The second line is failing with a null pointer exception, as if r hadn't been instantiated. But I'm setting it equal to a cell that that method retrieves, so it is obviously not null.

Why would I possibly be getting this error?

Upvotes: 0

Views: 124

Answers (4)

Makoto
Makoto

Reputation: 106508

The only way you'd be getting a NullPointerException is if r was indeed null. You can put this in your test conditions to ensure that, if r actually is null, then the test will fail:

RoomCell r = b.GetRoomCellAt(1, 2);
assertNotNull(r);
assertTrue(r.isDoorway());

If r is null, then the test fails early, and you avoid the NPE.

Upvotes: 0

newuser
newuser

Reputation: 8466

if(r != null)
{
  assertTrue(r.isDoorway());
}

instead of

assertTrue(r.isDoorway());


b.GetRoomCellAt(1, 2);

This cell may be null. So only you are getting nullPointerException

Upvotes: 0

Uri
Uri

Reputation: 89839

What's your full stacktrace? It is needed in order to determine which of the following is the cause:

It's possible that GetRoomCellAt doesn't find a value and returns null

It's possible that the implementation of GetRoomCellAt accesses a null pointer

It's possible that the implementation of isDoorway accesses a null pointer

FYI, it is good practice to use the @Nullable annotation to annotate parameters and return types

Upvotes: 3

Jesus Ramos
Jesus Ramos

Reputation: 23266

The function GetRoomCellAt() can probably still return NULL.

Upvotes: 2

Related Questions