Garbage Collection

Garbage collection in Java is the process by which Java programs perform automatic memory management. Java programs compile to bytecode that can be run on a Java Virtual Machine, or JVM for short. When Java programs run on the JVM, objects are created on the heap, which is a portion of memory dedicated to the program. Eventually, some objects will no longer be needed. The garbage collector finds these unused objects and deletes them to free up memory.

Garbage collection in Java is a process that automatically frees up memory that is no longer being used by your program. It's like a cleaning service for your program's memory, taking care of objects that are no longer needed so that the memory they occupy can be reused for new objects.

Here's a simple way to understand it:

Creating Objects: In Java, when you create objects (like when you're creating new characters in a video game), these objects use up a portion of your computer's memory.
Using Objects: As long as your program is using these objects, they stay in memory. This is like having books out on a desk that you are currently reading.
No Longer Needed: Eventually, some objects are no longer needed. Maybe your program has moved on to a different task, just like you might finish reading some of those books. But, just finishing reading doesn't automatically put the books back on the shelf.
Garbage Collection Kicks In: This is where garbage collection comes in. Java has a built-in garbage collector whose job is to find these "no longer needed" objects and free up the memory they occupy. It's like someone comes in, sees the books you're done with, and puts them back on the shelf for you.
Reusing Memory: Once the memory is freed up, Java can use that space for new objects, just like you can use the cleared space on your desk for new books.

This process is automatic in Java. As a programmer, you generally don't need to manually manage memory, which is different from languages like C or C++ where you have to explicitly free memory. The garbage collector runs in the background, helping to ensure that your program doesn't run out of memory by cleaning up old, unused objects.

Why Garbage Collection?

When objects are no longer needed, they should be destroyed.
This frees up the memory that they consumed.
Java handles all of the memory operations for you.
Simply set the reference to null, and Java will reclaim the memory

How Does Garbage Collection in Java work?

Java garbage collection is an automatic process. Automatic garbage collection is 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. Any part of your program no longer references an unused or unreferenced object. So the memory used by an unreferenced object can be reclaimed. The programmer does not need to mark objects to be deleted explicitly. The garbage collection implementation lives in the JVM.

To destroy an object in Java, you need to make it eligible for garbage collection. This means that you need to remove all references to the object, so that there are no more active references to it in your program.

Once there are no more active references to the object, the garbage collector will eventually remove the object from memory.

// create an object
MyObject myObj = new MyObject();

// set myObj reference to null
myObj = null;

// Call garbage collector
System.gc();

In this example, we create an object called myObj of type MyObject. Then, we set the reference myObj to null, which means that there are no more active references to the object. Finally, we call the garbage collector using the System.gc() method. This will remove the object from memory at some point in the future.

Note that calling System.gc() does not guarantee that the garbage collector will run immediately or that the object will be destroyed immediately. The garbage collector is a non-deterministic process and it will run on its own schedule.

Notes on `System.gc()`

The use of System.gc() in Java is a topic of some debate among developers. System.gc() is a call that suggests to the Java Virtual Machine (JVM) to initiate garbage collection. However, whether or not this call is necessary or even advisable depends on several factors.

The Role of `System.gc()`

Suggestion, Not a Guarantee: System.gc() suggests to the JVM that it is a good time to perform garbage collection, but it does not guarantee that the garbage collector will actually run. The JVM's garbage collector algorithm and the current state of the system ultimately determine whether it will act on this suggestion.
JVM Optimization: Modern JVMs are highly optimized and have sophisticated garbage collection algorithms designed to manage memory efficiently. They continuously monitor the runtime environment and make informed decisions about the best time to perform garbage collection based on the goal of maximizing performance and minimizing pause times.

Conclusion

In most cases, it's best to leave garbage collection to the JVM and focus on writing efficient, memory-friendly code. Use System.gc() sparingly, if at all, and consider it mainly as a tool for debugging and testing rather than a feature to rely on in production code. Modern JVMs are equipped with garbage collection algorithms that are efficient for a wide range of applications, making explicit garbage collection requests unnecessary and often counterproductive.

Notes on System.gc()

The Role of System.gc()

Conclusion

Notes on `System.gc()`

The Role of `System.gc()`