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The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java's dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected. (A more complete description of our garbage collection algorithm might be "A compacting, mark-sweep collector with some conservative scanning".) The garbage collector runs synchronously when the system runs out of memory, or in response to a request from a Java program. Your Java program can ask the garbage collector to run at any time by calling System.gc(). The garbage collector requires abou...

The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java's dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected. (A more complete description of our garbage collection algorithm might be "A compacting, mark-sweep collector with some conservative scanning".) The garbage collector runs synchronously when the system runs out of memory, or in response to a request from a Java program. Your Java program can ask the garbage collector to run at any time by calling System.gc(). The garbage collector requires abo...

Does 'static' cause Memory Leak in Java? What's memory leak? In simple terms, it's unused but referenced (somehow because the programmer probably unintentionally forgot to remove the references once the use of the object was over) part of the memory. Before we start discussing if 'static' can cause memory leak in Java, let me assure you that whatever you've read about Garbage Collectors in Java, is still valid and it certainly takes care of most (almost all) of the memory allocation/reclaimation of Java objects. But, that alone doesn't remove the possibility of the presence of memory leak in a Java program - just for example, you might not only be using only Java objects in your Java program. Putting it differently, what if you have used some native objects and forgot to reclaim the memory explicitly because that's anyway not going to be taken care by the GC (which takes care of heap memory management only)... right? Now that we agree with the pos...

Q1) Which part of the memory is involved in Garbage Collection? Stack or Heap? Ans) Heap Q2)What is responsiblity of Garbage Collector? Ans) Garbage collector frees the memory occupied by the unreachable objects during the java program by deleting these unreachable objects. It ensures that the available memory will be used efficiently, but does not guarantee that there will be sufficient memory for the program to run. Q3) Is garbage collector a dameon thread? Ans) Yes GC is a dameon thread. A dameon thread runs behind the application. It is started by JVM. The thread stops when all non-dameon threads stop. Q4)Garbage Collector is controlled by whom? Ans) 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, but this behavior of jvm can not be guaranteed. One can request the Garbage Collection to happen f...

An object that has been eligible for garbage collection may stop being eligible and return to normal life. Within a finalize() method, you can assign this to a reference variable and prevent that object's collection, an act many developers call resurrection .   The finalize() method is never called more than once by the JVM for any given object. The JVM will not invoke finalize() method again after resurrection (as the finalize() method already ran for that object). For example,   class Obj { protected void finalize(){ System.out.println("finalize invoked"); System.out.println("resurrect this object"); Program.objRef = this; //resurrection } } public class Program { static Obj objRef = null; public static void main(String args[]) { objRef = new Obj(); for(int i=0;i<2;i++){ method(i); System.out.println("objRef = " + objRef); } } static void method(int i) { S...

You may already know that when an object is not referenced by other objects, it's eligiable for garbage collection. But do you know the following two statemenats are also true? "If an object obj1 is garbage collected, but another object obj2 contains a reference to it, then obj2 is also eligible for garbage collection" "If object obj2 can access object obj1 that is eligible for garbage collection, then obj2 is also eligible for garbage collection" This is called "Island of Isolation". An "island of isolation" describes one or more objects have NO references to them from active parts of an application. In When is an object eligible for garbage collection? , we talked about: any object, that are not accessible from root set of references, is eligible for garbage collection. If object obj1 is eligible for garbage collection meaning it is not reachable by any objects from root set of references. Then the garb...

An object is eligible for garbage collection when there are no more root set of references to that object. References that are held in a variable are usually dropped when the variable goes out of scope.   What are root set of references? The object references in the local variables, operand stack of any stack frame and any object references in any class variables , and object references that were passed to native methods that either haven't been "released" by the native method. In Reference Objects and Garbage Collection : An executing Java program consists of a set of threads, each of which is actively executing a set of methods (one having called the next). Each of these methods can have arguments or local variables that are references to objects. These references are said to belong to a root set of references that are immediately accessible to the program. Other references in the root set incl...

Yes, there could be memory leak in Java applications. Wait a minute, doesn't Java virtual machine have a garbage collector that will collect and free all unreferenced memory automatically? Let's find out in general what memory leaks are, and how they occur in applications. If an application fails to return the not-in-use memory back to the heap, the "lost" memory is called memory leak. Memory leaks occur when the application doesn't free the memory allocated, usually are the objects no longer in use, but the object references are lost. If an object is no longer accessible, there is no way to free its memory. Each time such a leak is re-created, additional memory is used and not freed. Eventually, the process that runs the application will run out of memory and crash. It's true that for other programming languages, such as C/C++, there is not such a thing called garbage collector. The programmer is responsible for freeing the memory when the ...

An object becomes eligible for garbage collection when it becomes unreachable by any code. Two way can make this happened: Explicitly set the reference variable that refers to the object to  null . Reassign the reference variable that points to the object to refer to other object. For example, class Program { public static void main(String[] args) { X x1 = new X("1"); X x2 = new X("2"); x1 = null; // X("1") object is eligible for collection after this x2 = new Y(); // X("2") object is eligible for collection after this } } Did you like the above article? Please share with your friends..

Explain Garbage collection mechanism in Java? Garbage collection is one of the most important features of Java. The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources can be reclaimed and reused. A Java object is subject to garbage collection when it becomes unreachable to the program in which it is used. Garbage collection is also called automatic memory management as JVM automatically removes the unused variables/objects (value is null) from the memory. Every class inherits finalize() method from java.lang.Object, the finalize() method is called by garbage collector when it determines no more references to the object exists. In Java, it is good idea to explicitly assign null into a variable when no more in use. In Java on calling System.gc() and Runtime.gc(), JVM tries to recycle the unused objects, but there is no guarantee when all the objects will garbage collected. Garbage collection is an automatic pro...

The Java runtime environment deletes objects when it determines that they are no longer being used. This process is known as garbage collection. The Java runtime environment supports a garbage collector that periodically frees the memory used by objects that are no longer needed. The Java garbage collector is a mark-sweep garbage collector that scans Java's dynamic memory areas for objects, marking those that are referenced. After all possible paths to objects are investigated, those objects that are not marked (i.e. are not referenced) are known to be garbage and are collected. (A more complete description of our garbage collection algorithm might be "A compacting, mark-sweep collector with some conservative scanning".) The garbage collector runs synchronously when the system runs out of memory, or in response to a request from a Java program. Your Java program can ask the garbage collector to run at any time by calling System.gc(). The garbage collector requires abo...