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Java has automatic memory management. Garbage collector is part
of JVM responsible for recycling the allocated memory to java objects.
Garbage Collection cannot be forced explicitly. JVM may do
garbage collection if it is running short of memory.
The call System.gc()
or ( new
Runtime().gc() ) does not force the garbage collection but only
suggests that the JVM may make an effort to do garbage collection.
Garbage Collection is hardwired in Java runtime system. Java
runtime system keeps the track of memory allocated. Therefore, it is able to
determine if memory is still usable by any live thread. If not, then garbage
collector will eventually release the memory back to the heap.
Garbage Collection usually adopts algorithm, which gives fair
balance between responsiveness (how quickly garbage-collection completes) and
speed of memory recovery. Responsiveness is especially important in real time
systems whereas quick memory-recovery is important for memory-intensive
operations.
How an object becomes eligible for Garbage Collection
q An object is eligible for garbage collection when no object refers to it.
q An object also becomes eligible when you explicitly set all its references to null.
q An object also becomes eligible when you explicitly reassign all its references to point to another object or null.
q Object created in method and referenced by method variables are eligible for garbage collection when the method returns unless its reference is returned by method.
q You can not …
Force garbage collection
Know exactly when it will happen
Know for sure which algorithms are used for garbage collection
q You can ….
Tell when the object becomes eligible for garbage collection
Explicitly make an object eligible for garbage collection
Request garbage collection
q The finalize() method
It is called only once by the garbage collector before deleting
unreachable object.
As garbage collector makes no guarantees, the finalize()method
may never run
You can make object ineligible for garbage collection in the finalize() method.