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Can I stop JVM performing garbage collection?

I want to know if there is a way to stop and start the JVM performing Garbage Collection during runtime.
If there is not, why not? Surely this feature would make Java more suitable for safety critical applications?

Actually, there is a way to stop Java GC. Just use the Epsilon GC algorithm that was introduced as an experimental feature in Java 11. Just add the following two arguments to your JVM's startup script:
-XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC
All or Nothing
Now just keep in mind that this Java GC algorithm does no GC at all. So if you do any object allocation in your code, eventually you'll hit an OutOfMemoryError and your app will crash. But if your JVM is short lived, and you don't think that's an issue, give Epsilon GC a try.
Just remember it's all or nothing. You can't force Java GC and you can't stop Java GC from happening if you use any of the other garbage collectors. The collector is non-deterministic, so control by programmers or admins just isn't possible out of the box.

By default the JVM runs the JVM only needed. This means you can't turn off the GC or your program will fail.
The simplest way to avoid stopping the JVM is;
use a very small eden size so when it stops it will be less than some acceptable time.
or make the eden size very large and delay the GC until it hardly matters. e.g. you can reduce you garbage rate and run for 24 hours or longer between minor GCs.

How to perform Garbage Collection in win 7?

I'm very new to Java. I found in this link an easy way (without any programming) to increase assigned JVM memory in win 7 http://www.wikihow.com/Increase-Java-Memory-in-Windows-7
My question: Is there a similar way to perform (force) garbage collection in Win 7? I mean something like System.gc() but in windows
I need it to be in Windows without going into details of Heap analysis and stuff like that

Forget about GC. If you're having OutOfMemoryError (and there is nothing in your code screwing up your memory usage, because if that's the case you should fix it first) you need to increase the heap size.
There are two parameters that will help you with that: Xmx and Xms. The first is the most important, since it defines the maximum memory a Java application can use. The second defines the initial heap size, but the JVM will increase it if it's needed, until it reaches the maximum value.
You can check this question to read about these parameters: What are the Xms and Xmx parameters when starting JVMs?

You cannot force jvm to perform garbage collection. You can only request it by using System.gc() method or Runtime.gc() method.
To increase the chances for garbage collection use this code:
for(int i=0;i<2000;++i)System.gc();
This will higher chances for garbage collection to be performed.

The first thing you must know about Java is that it is 99% platform-independent so asking a question specifically for Windows is usually unrelevant. The garbage collection occurres within the JVM, it has nothing to do with the operating system running the JVM. By the way, there is no way to force an immediate GC, as the doc of System.gc explains it :
Calling the gc method suggests that the Java Virtual Machine expend
effort toward recycling unused objects in order to make the memory
they currently occupy available for quick reuse. When control returns
from the method call, the Java Virtual Machine has made a best effort
to reclaim space from all discarded objects.

If you mean from the command line you can do
on windows
jmap -histo:live {pid} > nul
on linux
jmap -histo:live {pid} > /dev/null
This will trigger a full GC from the command line.
You should never need to do this except perhaps for exotic test cases.

How to perform Garbage Collection in win 7?
Empty the recycle bin!
Just kidding. The tutorial you linked describes how to increase the upperbound of memory attributed to Java processes. Giving them more memory could allow them to run faster I they are memory hungry. This has nothing to do with triggering a single garbage collection.
You can't do the same (i.e. attributing more memory) with Window since Windows is the operating system which controls and manages the available memory.

Can we call the Garbage Collector explicitly? [duplicate]

This question already has answers here:
Why is it bad practice to call System.gc()?
(13 answers)
Closed 9 years ago.
My application has lot of iterations. Till now I haven't faced any memory issues. But from code level I can suspect there are few places, which causes memory leaks and out of memory problem. I am thinking of calling garbage collector manually. Is it good practice to call Garbage Collector manually?

You can call Garbage collector using:
System.gc();
But this does not mean that it'll be executed immediately. The JVM decides when to execute it. In general if the JVM is about to throw an OutOfMemoryError, calling System.gc() won't prevent it. Better investigate why you're leaking so much memory and clean it up along the way.
JavaDoc:
Calling the gc method suggests that the Java Virtual Machine expend
effort toward recycling unused objects in order to make the memory
they currently occupy available for quick reuse. When control returns
from the method call, the Java Virtual Machine has made a best effort
to reclaim space from all discarded objects

Is it good practice to call Garbage Collector manually?
No, it is definitely not good practice.
You can use System.gc(). Note that this is not guaranteed to call the garbage collector - it only gives a hint to the system that it might be a good idea to do garbage collection.
The garbage collector in Oracle's JVM contains a lot of sophisticated logic to determine when and what to cleanup. Tuning it requires knowledge about details on how it works. Just putting a System.gc() somewhere in your program is not likely to help a lot, and in fact, it can even make it worse.
See Java SE 6 HotSpot Virtual Machine Garbage Collection Tuning for details on how to tune garbage collection with Java SE 6.

Yes you can explicitly call garbage collector using
System.gc();
But what happens is that you can't order JVM to do garbage collection immediately. JVM decides on its own when to garbage collect.Hence its not a good idea of calling it manually.
Moreover regarding OutOfMemoryException doing manual garbage collection won't help you prevent the exception, since JVM throws this exception after reclaiming all the memory it can. It has some very sophisticated algorithms to determine when and how to do perform the garbage collection.
So what i suggest is that if you are getting OutOfMemoryException then recheck your program make it more efficient or increase heap space.

You can call Garbage Collector explicitly, but JVM decides whether to process the call or not.
Ideally, you should never write code dependent on call to garbage collector.
JVM internally uses some algorithm to decide when to make this call. When you make call using System.gc(), it is just a request to JVM and JVM can anytime decide to ignore it.

Regardless of whether you can or cannot manually trigger the garbage collector (and the different levels of collection), and what impact this has on performance (which indeed is a topic worth discussion), it will not prevent OutOfMemoryErrors, because when the JVM is about to run out of memory, it does the most thorough collection it can anyway. Only if after that collection not enough memory is available, will it error out. Even if you trigger the collection earlier yourself, the result (the amount of memory reclaimed) is the same.
Memory leaks cannot be fixed by running garbage collection more often.
They have to be fixed in your program (stop referencing things you don't need anymore earlier), or (worst case, if it is a "real" leak) in the JVM or runtime library itself (but genuine memory management bugs should not exist anymore after so many years of service).

Calling System.gc() does not guarantee any GC. Garbage is collected if there is a real need for memory.
You can have a look at different garbage collectors here.
http://javarevisited.blogspot.in/2011/04/garbage-collection-in-java.html
You can include any of these GCs in your command line params as per your needs.

Does the Garbage collector in Java work automatically?

I need to to know whether the Garbage Collector in Java works on its own or we do need to start it.

It works on its own. You can "suggest" that it run, but that's about it.

The GC is a deamon thread that's started with your JVM and ends when your JVM ends (JVM is stoped if no more non-deamon threads exist).
It runs in background and kicks into action when/if needed. The JVM decides when it runs and you can "request" it to run with System.gc().
But I should mention that you must not write your code to depend on the GC to run (finalizers in Java are not like destructors in C++). People tend to count to much on the GC and then forget about it which is a no-no and leads to memory leaks and hard to find bugs.
What you can count on is that before you get a java.lang.OutOfMemoryError, the GC kiked into action and did its best.

It works on its own according to an optimized algorithm to get the optimal performance. You can perform a force garbage collection but it is not recommended because it can block the normal Garbage collection pattern reducing the actual performance.
You should read this Old SO Discussion on a related topic.

Yes, garbage collection is automatically handelled by Java.
When an object is no longer referred to by any variable, Java automatically reclaims memory used by that object. This is known as garbage collection.
Still the method
System.gc() method may be used to call it explicitly.

The only occasion I know of where you have to call System.gc() is when you are creating lots of Direct ByteBuffers. For heap memory, an OutOfMemoryError will only occur after a Full GC, however for direct memory, if you run out (even though there might be buffers which are not referenced), no GC is called and so you might have to call it yourself before trying again.
I would hope this is something which is fixed in future versions of Java.

(This is probably just repeating what other answers were trying to say ... However, it is worth saying this clearly.)
The Java garbage collector runs automatically as required, and there is no need to start it.
There is a static method (System.gc()) that an application can call to request that the garbage collector run "now". However:
The JVM can be configured to pay no attention to this request.
It is generally a bad idea to make this request because it can significantly degrade garbage collector performance. Generally speaking, the best time to run the garbage collector is when there is lots of garbage to be collected, and only the JVM knows when that is likely to be.
EDIT - the cure for large garbage collection latencies is to change the JVM's garbage collector properties to select the low latency collector. Calling System.gc() is not the way to deal with this in a modern JVM.

How can I disable Java garbage collector?

We have a PHP webapp that calls a Java binary to produce a PDF report (with JasperReports). The Java binary outputs the PDF to standard output and exits; the PHP then sends the PDF to browser. This Java command lasts about 3 to 6 seconds, and I think when it lasts 6 second it's because the GC kicks in. I would like to disable the GC because anyway when the command exits all memory is returned.
I would like to know how to disable it for Java 1.4.2 and for Java 1.6.0 because we are currently testing both JVM to see which performs faster..

It sounds like you are trying to save time, but going about it the wrong way. The time saved in disabling garbage collection would be trivial (for a single task) compared to the time taken to launch and shutdown the java process. You might want to consider having a java process launch that you can ask multiple times to do the work you require if run-time performance is your goal.

There is no way to disable garbage collection entirely. Garbage collection is only run when the JVM runs out of space, so you could give the program more memory. Add these command line options to the Java command
-Xmx256M -Xms256M
This gives the program 256Mb of ram (the default is 64Mb). Garbage collection will not take 3 seconds for a default size JVM though, so you might want to investigate more closely what the program is doing. Yourkit profiler is very useful for figuring out what is taking a long time.

GC only kicks in when JVM is short on memory, so you either GC or die. Try turning on verbose GC and see if it actually takes significant amount of time.
java -verbose:gc

Java 11 comes with an no-op garbage collector.
It can be enabled by the -XX:+UseEpsilonGC option at JVM start.
According to the JEP decription one of its goals is to make certain short-lived jobs more efficient, what might be you use case:
Extremely short lived jobs. A short-lived job might rely on exiting quickly to free the resources (e.g. heap memory). In this case, accepting the GC cycle to futilely clean up the heap is a waste of time, because the heap would be freed on exit anyway. Note that the GC cycle might take a while, because it would depend on the amount of live data in the heap, which can be a lot.

Java 11 gives you the binary option to either have Java GC on, or have Java GC turned off. To turn off Java GC you use the Epsilon Garbage Collector which must be turned off on the command line. On Java 11, use the following two JVM arguments:
-XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC
Without the UnlockExperimentalVMOptions argument, the JVM will fail to start, so make sure it's included.
Can't Stop Java GC
Unfortunately, if you're not using Epsilon GC, there is no way to disable, stop or prevent garbage collection from happening. Just like not being able to trigger GC, you can't stop Java GC either. The algorithms are non-deterministic. Only the JVM can control when they occur.

You can use the -Xmx option to set the maximum heap size; using a larger heap should prevent the VM from runnning out of memory and, thereby, requiring garbage collection so soon.

Are you sure that it is garbage collection causing the slowdown? Have you run java with -verbose:gc to see what is happening?
You cannot disable garbage collection on the JVM. You could however look at tuning the garbage collector for better performance.

Contrary to what everyone else has said, there is a way to suspend GC, though it's very convoluted.
If you call a native function via JNI, in between the native code calling GetPrimitiveArrayCritical and ReleasePrimitiveArrayCritical, GC is suspended. It has to do this because it is the mechanism used for sharing memory between Java and native code, and GC may move objects around in memory.
So to utilise this you'd need to create a JNI function which calls the former, then polls a flag written to that critical array (which could just be a byte[1]) waiting till it sees the flag before calling the latter. When the Java code wishes to suspend GC it would call the JNI method and when it wishes to resume GC, set the aforementioned flag (I believe reads/writes to the critical array are volatile, so the native code would see the flag immediately).
Now I'm not saying this is a good idea, and certainly not the correct solution to the OP's problem. But if you absolutely had to temporarily suspend GC for some reason (perhaps you wish to manipulate raw memory via sun.misc.Unsafe and needed to ensure objects were not moved about by GC whilst doing so), that's how you could achieve it.

As everyone as said you can't disable GC in the JVM, which makes sense right, because if you could there'd be memory leaks due to java not having an explicit way for the developer to delete the heap data.
Do you have access to the source of this java binary? If so it might be worth analysing it and seeing if there's any bottle-necks which could be better written to cut down on GC activity. This could be done with most java profilers, like JProbe for example.

To avoid garbage collector release a variable or property from any object,
you must set this property (released by gc) as static in your class
it was my solution.
Example:
private static String myProperty;