GC garbage collection

GC means garbage collection (Gabage Collection), and memory processing is a place where programmers are prone to problems. Forgetting or wrong memory recycling can lead to programsOr the system is unstable or even crashes. The GC function provided by Java can automatically monitor whether the object exceeds the scope to achieve the purpose of automatic memory recovery. The Java language does not provide a display operation method to release the allocated memory.

What is the rationale for the garbage collector?

For GC, when the programmer creates an object, the GC starts to monitor the address, size and usage of the object.Generally, GC records and manages all objects in the heap in a directed graph manner.In this way it is determined which objects are "reachable" and which objects are "unreachable".When the GC determines that some objects are "unreachable", it is the responsibility of the GC to reclaim the memory space.

Can the garbage collector reclaim memory right away?Is there any way to proactively notify the virtual machine for garbage collection?

Yes. Yes.Programmers can manually execute System.gc() to notify the GC to run, but the Java language specification does not guarantee that the GC will be executed.

Key points of the garbage collection mechanism
1. The garbage collection mechanism only reclaims the object space in the JVM heap memory.
2. Powerless to other physical connections, such as database connection, input stream output stream, Socket connection.
3. The current JVM has a variety of garbage collection implementation algorithms, with different performances.
4. The occurrence of garbage collection is unpredictable, and the program cannot precisely control the execution of the garbage collection mechanism.
5. The reference variable of the object can be set to null, implying that the garbage collection mechanism can recycle the object.
6. Programmers can notify the system to perform garbage collection through System.gc() or Runtime.getRuntime().gc(). There will be some effects, but it is still uncertain whether the system will perform garbage collection.
7. Before any object is reclaimed by the garbage collection mechanism, its finalize method is always called first (if the method is overridden and the object is re-referenced by a new reference variable, the object will be reactivated).
8. Never actively call the finalize method of an object, it should be called by the garbage collection mechanism.