HELP!! I dont see how i am continually getting a NullPointerException (java)!!!

[wickster]

Hey everyone,

I am wrote a class called ScopedMap which is very similar to the HashMap class, only it has multiple layers (levels) which act like a scope (hence the name). Unfortunately in one of my other class files which use it, I cannot seem to get around a null pointer exception when i call the get method. Here is the code:

import java.util.HashMap;

public class ScopedMap<K,V>{
	
	private int nestingLevel = 0;
	private HashMap<Integer, HashMap<K,V>> scope = new HashMap<Integer, HashMap<K,V>>();

	public ScopedMap(){
	// does nothing
	}

	public void enterScope(){
	
	nestingLevel++;
	if(scope.get(nestingLevel) == null){
		scope.put(nestingLevel, new HashMap<K,V>());
	}
	}

	public void exitScope(){
	if(nestingLevel>0)  // nesting level cannot be negative
		nestingLevel--;
	}

	public void put(K key, V value){
	if(scope.get(nestingLevel) == null){
		scope.put(nestingLevel, new HashMap<K,V>());
		scope.get(nestingLevel).put(key, value);
	}
	else scope.get(nestingLevel).put(key, value);
	}

	public V getLocal(K key){
		return scope.get(nestingLevel).get(key);
	}

	public V get(K key){
	int temp = nestingLevel;
	while(temp>=0){
		if(scope.get(temp).containsKey(key)){   // Here is line 40, where the exception occurs.....
			return scope.get(temp).get(key);
		}
		else temp--;
	}
	return null;
	}

	public int getNestingLevel(){
		return nestingLevel;
	}
}

I get the following error:
Exception in thread "main" java.lang.NullPointerException
at ScopedMap.get(ScopedMap.java:40)
at Reader.main(Reader.java:4

ANY HELP WOULD BE GREATLY APPRECIATED!!!

Thanks,
Tom

[SuSEholic]

Change this

		if(scope.get(temp).containsKey(key)){
			return scope.get(temp).get(key);
		}

With this

            HashMap h = scope.get(temp);
            if (null != h && h.containsKey(key))
            {
                return h;
            }

That's happen if the "scope" has no value for key "temp", it will return "NULL", so it'll throw NullPointerException if you're trying to access it.

ANY HELP WOULD BE GREATLY APPRECIATED!!!

Hey, I get a greatly appreciation .

[wickster]

Thanks a bunch!!!!!!!