Weak Reference in Java

Today, during a phone interview, I was asked a question about WeakReference in Java.  I only knew that the weak referenced object can be garbage collected by JVM, and nothing more.  I did a little research, and realized that there are 4 types of references in Java:

1. Strong Reference
2. Soft Reference
3. Weak Reference
4. Phantom Reference

They are in the order from strong to weak references.  3 classes, SoftReference, WeakReference, and PhantomReference are for the last 3 references.  For strong reference, just use new operator. Below is a great blog talking about all 4 references:

Understanding Weak References