WeakReference and SoftReference were added into Java API from long time but not every Java programmer is familiar with it. Which means there is a gap between where and how to use WeakReference and SoftReference in Java. Reference classes are particularly important in context of How Garbage collection works. As we all know that Garbage Collector reclaims memory from objects which are eligible for garbage collection, but not many programmer knows that this eligibility is decided based upon which kind of references are pointing to that object. This is also main difference between WeakReference and SoftReference in Java. Garbage collector can collect an object if only weak references are pointing towards it and they are eagerly collected, on the other hand Objects with SoftReference are collected when JVM absolutely needs memory. These special behaviour of SoftReference and WeakReference makes them useful in certain cases e.g. SoftReference looks perfect for implementing caches, so when JVM needs memory it removes object which have only SoftReference pointing towards them. On the other hand WeakReference is great for storing meta data e.g. storing ClassLoader reference. If no class is loaded then no point in keeping reference of ClassLoader, a WeakReference makes ClassLoader eligible for Garbage collection as soon as last strong reference removed. In this article we will explore some more about various reference in Java e.g. Strong reference and Phantom reference.
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