What types of references in Java do you know?

In Java, there are the following types of references that manage object lifetimes and garbage collection:

1. Strong Reference — a normal reference that prevents the object from being garbage collected. As long as strong references exist, the object will not be removed.

2. Soft Reference — used for caching. Objects with soft references will only be garbage collected when the JVM needs memory.

3. Weak Reference — objects with such references can be collected during the next garbage collection cycle, even if weak references still exist.

4. Phantom Reference — used to track when an object is ready to be collected but has not yet been removed. It allows performing additional actions after the object’s finalization.

Example of creating a weak reference:

Object obj = new Object();
WeakReference<Object> weakRef = new WeakReference<>(obj);
obj = null; // now the object is only accessible through the weak reference

These types of references help manage memory and optimize object handling, especially in caches and resource-constrained systems.