CODEWITHSUNDEEP
java
Christopher
Christopher

Reputation: 31

HashMap.get() returns null even though element exists

From within my code, I add an entry to a HashMap. Later, when trying to get the element by its key, it returns null.

Can't post images yet, but after debugging this is what it says:

https://i.sstatic.net/vf1bW.png https://i.sstatic.net/NxxEI.png

Please help me solve this really weird error!

EDIT: Since you requested, these are the addEntry() and getEntry() methods and the place in code where they are called:

backgroundActor = new BackgroundActor(new BackgroundGraphicsComponent());
backgroundActors.addEntry(backgroundActor, "Background");
borderActor = new BorderActor(new BorderPhysicsComponent(), new BorderGraphicsComponent());
backgroundActors.addEntry(borderActor, "Border");

@SuppressWarnings("unchecked")
    @Override
    public T getEntry(String key) {
        if (gameObjects.get(key) != null) {
            return (T) gameObjects.get(key);
        }
        else throw new NullPointerException(); // this is where it fails
    }

    @Override
    public void addEntry(T gameObject, String key) {
        if (gameObject != null) gameObjects.put(gameObject, key);
        else throw new NullPointerException();
    }

EDIT2: Solved. The problem was with the put() method of HashMap that takes as its first argument the key and then the value. Thanks to Nizil and user1498360!

Upvotes: 0

Views: 2490

Answers (2)

RajeshCh
RajeshCh

Reputation: 21

Please change:

if (gameObject != null) gameObjects.put(gameObject, key);

to:

if (gameObject != null) gameObjects.put(key, gameObject);

I hope this will solve your problem.

Upvotes: 1

NiziL
NiziL

Reputation: 5140

The put method of Map take as first argument the key, then the value.

So in your addEntry method, you should do: 

gameObjects.put(key, gameObject);

Instead of

gameObjects.put(gameObject, key);

This explain why your debugger print {BackgroundActor=Background, BorderActor=Border} instead of {Background=BackgroundActor, Border=BorderActor}

Upvotes: 4

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