What are the differences between Strong, Soft, Weak, and Phantom references in memory management?

In memory management in Java (and Android), there are different types of references that affect garbage collection:

• Strong Reference — a normal reference that prevents the object from being collected by the garbage collector as long as the reference exists.

• Soft Reference — an object with a soft reference will only be collected when the JVM is low on memory. Used for caching, when it is desirable to keep the object but it can be freed if necessary.

• Weak Reference — an object with a weak reference can be collected during the next garbage collection cycle, even if the reference exists. Used for references that should not prevent object collection.

• Phantom Reference — the weakest reference. The object is considered to be collected, but a phantom reference allows notification after the object has been collected, for example, to clean up resources.

Example of using a weak reference:

WeakReference<MyObject> weakRef = new WeakReference<>(myObject);
myObject = null; // now the object can be collected