If an object reference is set to null, will the Garbage Collector immediately free the memory held by that object ?

• No, the object will be available for garbage collection in the next cycle of the garbage collector.

What is the purpose of garbage collection in Java, and when is it used ?

• The purpose of garbage collection is to identify and discard those objects that are no longer needed by the application, in order for the resources to be reclaimed and reused.

When is the finalize() called ? What is the purpose of finalization? What is the purpose of overriding finalize() method? How many times does the garbage collector calls the finalize() method for an object? What happens if an uncaught exception is thrown from during the execution of the finalize() method of an object? How to enable/disable call of finalize() method of exit of the application

• The finalize method is called by the garbage collector, just before releasing the object’s memory.
• It is normally advised to release resources held by the object inside the finalize method.
• The finalize() method should be overridden for an object to include the clean up code or to dispose of the system resources that should to be done before the object is garbage collected.
• Only once.
• The exception will be ignored and the garbage collection (finalization) of that object terminates.
• Runtime.getRuntime().runFinalizersOnExit(boolean value) . Passing the boolean value will either disable or enable the finalize() call.

Does a garbage collector collect stack memory, heap memory, or both?

• It collects heap memory. Usually, stack memory is collected automatically when the execution path reaches the end of the scope.

How is Garbage Collection managed? Can the Garbage Collection be forced by any means? How can the Garbage Collection be requested?

• The JVM controls the Garbage Collector, it decides when to run the Garbage Collector. JVM runs the Garbage Collector when it realizes that the memory is running low.
• No. The Garbage Collection can not be forced, though there are few ways by which it can be requested there is no guarantee that these requests will be taken care of by JVM.
• There are two ways in which we can request the jvm to execute the Garbage Collection.
  • Runtime.gc(). The methods to perform the garbage collections are present in the Runtime class provided by java. The Runtime class is a Singleton for each java main program. The method getRuntime() returns a singleton instance of the Runtime class. The method gc() can be invoked using this instance of Runtime to request the garbage collection.
  • System.gc()

When does an Object becomes eligible for Garbage collection in Java ?

• A Java object is subject to garbage collection when it becomes unreachable to the program in which it is currently used.