What is the garbage collector in Java?

Question

I am new to Java and confused about the garbage collector in Java. What does it actually do and when does it comes into action. Please describe some of the properties of the

Answer 1

The garbage collector allows your computer to simulate a computer with infinite memory. The rest is just mechanism.

It does this by detecting when chunks of memory are no longer accessible from your code, and returning those chunks to the free store.

EDIT: Yes, the link is for C#, but C# and Java are identical in this regard.

Answer 2

Garbage collection refers to the process of automatically freeing memory on the heap by deleting objects that are no longer reachable in your program. The heap is a memory which is referred to as the free store, represents a large pool of unused memory allocated to your Java application.

Answer 3

Garbage Collection in Java (and other languages/platforms as well) is a way for the java run-time environment (JRE) to reuse memory from java objects that are no longer needed. Simplistically, when the JRE initially starts up it asks the Operating System (O/S) for a certain amount of memory. As the JRE runs your application(s) it uses that memory. When your application is done using that memory, the JRE's "Garbage Collector" comes along and reclaims that memory for use by different parts of your existing application(s). The JRE's "Garbage Collector" is a background task that is always running and tries to pick times when the system is idle to go on its garbage runs.

A real world analogy would be the garbage men that come to your house and pick up your recyclable garbage... eventually, its reused in other ways by yourself and/or other people.

Answer 4

It frees memory allocated to objects that are not being used by the program any more - hence the name "garbage". For example:

public static Object otherMethod(Object obj) {
    return new Object();
}

public static void main(String[] args) {
    Object myObj = new Object();
    myObj = otherMethod(myObj);
    // ... more code ...  
}

I know this is extremely contrived, but here after you call otherMethod() the original Object created is made unreachable - and that's "garbage" that gets garbage collected.

In Java the GC runs automatically, but you can also call it explicitly with System.gc() and try to force a major garbage collection. As Pascal Thivent points out, you really shouldn't have to do this and it might do more harm than good (see this question).

For more, see the wikipedia entry on Garbage collection and Tuning Garbage Collection (from Oracle)

Answer 5

Automatic garbage collection is the process of looking at heap memory, identifying which objects are in use and which are not, and deleting the unused objects. An in use object, or a referenced object, means that some part of your program still maintains a pointer to that object. An unused object, or unreferenced object, is no longer referenced by any part of your program. So the memory used by an unreferenced object can be reclaimed.

In a programming language like C, allocating and deallocating memory is a manual process. In Java, process of deallocating memory is handled automatically by the garbage collector. Please check the link for a better understanding. http://www.oracle.com/webfolder/technetwork/tutorials/obe/java/gc01/index.html

Answer 6

garbage collector implies that objects that are no longer needed by the program are "garbage" and can be thrown away.