The difference between the four references of "Java"

Strong reference: If an object has a strong reference, it will not be reclaimed by the garbage collector. Even if there is not enough memory space, the JVM does not reclaim it, but instead throws a outofmemoryerror error that causes the program to terminate unexpectedly. If you want to break the association between a strong reference and an object, you can explicitly assign a reference to NULL, so that the JVM reclaims the object at the appropriate time.
Soft references: when using soft references, if there is enough memory space, soft references can continue to be used without being reclaimed by the garbage collector, and soft references are reclaimed by the garbage collector only when there is insufficient memory.
Weak reference: an object with a weak reference has a more ephemeral life cycle. Because when the JVM is garbage collected, weak references are recycled whenever a weak reference object is found, regardless of whether the current memory space is sufficient. However, because the garbage collector is a low-priority thread, it is not always possible to quickly discover weak reference objects
Virtual Reference: as the name implies, is the form of a dummy, if an object only holds a virtual reference, then it is equivalent to no reference, at any time may be reclaimed by the garbage collector.

The difference between the four references of "Java"