What's the Difference Between Soft References and Weak References in Java?

What's the Hierarchy of References in Java?

SoftReferences vs. WeakReferences

While discussing references in Java, one often encounters the terms "soft references" and "weak references." What exactly do these two types of references represent, and how do they differ?

As the article "Understanding Weak References" by Ethan Nicholas explains, weak references are references that are not strong enough to keep an object in memory. This means that once there are no strong references pointing to an object, the garbage collector may remove it.

In contrast, soft references are like weak references, but they are less eager to discard the referenced object. Softly reachable objects remain in memory as long as there is sufficient memory available. If memory becomes scarce, the garbage collector may clean up soft references to free up space.

These properties make soft references ideal for caches, where objects can be stored for quick access as long as memory permits. If there's a shortage of memory, the least important objects (softly reachable ones) will be removed.

Furthermore, Peter Kessler observes that the Sun JRE treats soft references differently from weak references. The client JRE prioritizes removing soft references to maintain a smaller memory footprint, while the server JRE focuses on performance by expanding the heap instead of eliminating soft references.

The above is the detailed content of What's the Difference Between Soft References and Weak References in Java?. For more information, please follow other related articles on the PHP Chinese website!