How to use WeakReference in Java and Android development?

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Using a WeakReference in Android isn’t any different than using one in plain old Java.

You should think about using one whenever you need a reference to an object, but you don’t want that reference to protect the object from the garbage collector. A classic example is a cache that you want to be garbage collected when memory usage gets too high (often implemented with WeakHashMap).

Be sure to check out SoftReference and PhantomReference as well.

EDIT: Tom has raised some concerns over implementing a cache with WeakHashMap. Here is an article laying out the problems: WeakHashMap is not a cache!

Tom is right that there have been complaints about poor Netbeans performance due to WeakHashMap caching.

I still think it would be a good learning experience to implement a cache with WeakHashMap and then compare it against your own hand-rolled cache implemented with SoftReference. In the real world, you probably wouldn’t use either of these solutions, since it makes more sense to use a 3rd party library like Apache JCS.

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