Reference Objects and Garbage Collection

Unreachable objects (outside the strongly and weakly reachable areas) are not reachable from the root set.

Strongly reachable objects (inside the strongly reachable area to the lower left) are reachable through at least one path that does not go through a reference object.

Weakly reachable objects (inside the weakly reachable area shown enclosed with a dashed line to the upper-right) are not strongly reachable through any path, but reachable through at least one path that goes through a weak reference.

Weakly reachable objects are finalized some time after their weak references have been cleared. The only real difference between a soft reference and a weak reference is that the garbage collector uses algorithms to decide whether or not to reclaim a softly reachable object, but always reclaims a weakly reachable object.

Java API Package: java.lang.ref.*