Java - EnumSet.add(enum), throws NullPointerException

Question

This is in Java, cross platform and being debugged on a computer running Ubuntu Oneric with OpenJDK installed as my runtime. I have an EnumSet for checking inside of in a class in a game I'm working on. I have this readout from logcat, from debug aplenty in my constructor: ``` Tile : passability being set...? Exception in thread "Thread-1" javax.media.opengl.GLException:java.lang.NullPointerException ... Caused by: java.lang.NullPointerException at net.darkglass.map.Tile.addPassability(Tile.java:144) ... ``` Not amusing. Tracking it down, my problem seems to be, entirely, this line: ``` public void addPassability(Passability type) { this.passability.add(type); } ``` By which I mean the body of that function. It is called from the constructor as: ``` this.addPassability(Passability.AIR); ``` When the NullPointerException happens. In the body of the Passability Enum Type, I have ``` public enum Passability { AIR, ALL, GROUND, NONE, SIGHT, SKILL, STRUCTURE, WATER; } ``` as, quite literal…

Accepted Answer

So you've declared the `passability` variable, but you've shown no sign of it being assigned a value other than the default value of `null`. Perhaps you meant:

```
private EnumSet<Passability> passability = EnumSet.noneOf(Passability.class);
```

An `EnumSet` is an object, like any other - so unless you explicitly give your variable, it will have the default value of `null` and when you call `add` on it, you'll get a `NullPointerException` - which is exactly what's happened here.

Java - EnumSet.add(enum), throws NullPointerException

Solution

Problem