Null pointer exception with static Map

Question

It's 5am and I'm a bit asleep, so that may be it (also I'm relatively new with Java). But I don't see why this code generates Null Exception with this code. The map should be initialized by then, shouldn't it?

private static final Map<String, Integer> CONDS_MAP = 
    Collections.unmodifiableMap
    (
        new HashMap<String, Integer>()
            {{ 
                put("null", 0);
                put("false", 0);
                put("true", 1);
                put("numElems.lt", 2);
                put("NELT", 2);
                put("numElems.gt", 3);
                put("NEGT", 3);
            }}
    );

private int getCodeInt(Object code)
{
    if (code.getClass() == String.class)
    {
        return CONDS_MAP.get((String)code); // Null Exception here
    }
    else
    // (... etc etc)
}

Thanks! and sorry it it is too trivial...

Unrelated, but try to avoid the double brace HashMap initializer, and code.getClass() == String.class should be code instanceof String (easier to read, faster to type, avoids possible NPE). — Thilo
– Thilo, Commented Sep 23, 2011 at 3:42

Thilo · Accepted Answer · 2011-09-23 03:45:07Z

6

It is most likely caused by trying to unbox the null returned from a non-existing key.

return CONDS_MAP.get((String)code);

is the same as

return CONDS_MAP.get(code).intValue();

That last intValue will fail if the Map returns null.

answered Sep 23, 2011 at 3:45

Thilo

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4 Comments

huff Over a year ago

I could swear that I put the dot in that json... but nah, code was "numElemsgt". Thanks. Sleeping may help. And also I will check for null values.

huff Over a year ago

Different strings should return the same int. (I'll update the example)

Thilo Over a year ago

Sure, but you could still say put(NUM_ELEMS_GT, 3); instead of put("numElems.gt", 3);

huff Over a year ago

I don't see it working for me: I am using for reading data from a JSON file, and converting some Strings from the file to integer codes that later on are going to be switch'd.

Oscar Gomez · Accepted Answer · 2011-09-23 03:39:22Z

0

Yes it has been initialized by then, the nullpointerexception is probably caused by a null key.

answered Sep 23, 2011 at 3:39

Oscar Gomez

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2 Comments

Thilo Over a year ago

Does a null key cause a NullPointerException ?

Oscar Gomez Over a year ago

@Thilo Yes according to the docs - download.oracle.com/javase/6/docs/api/java/util/…

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