JVM garbage collection overview

Learning with problems is more conducive to focusing our attention , I bring questions to this chapter .

1. What is rubbish ？

Simple question , But often many people can't answer , This is a misunderstanding in thinking , Well, not much bb 了 .

simply , When an object is not pointed to by any reference , Then it becomes garbage , If a person is not needed by anyone , Then he is garbage ( The example is not good , The dog's head lives ).

When there is more garbage like this , Without being cleaned up in time , It is easy to cause memory overflow .

2. Why garbage collection is needed ？

Connect with life , If the garbage is always there , So over time , The room becomes a garbage dump , Can you still live ？

The same is true for programs , Eventually, the memory is exhausted , There are only a bunch of useless objects left , Wasted resources .

And once there is garbage collection , Useless objects are cleaned up , The extra space can store new objects .

3. Early memory management

We all know ,Java There is an automatic garbage collection mechanism , This is also C,C++ What programmers envy , Because they need to make a manual memory request , Memory free , And if you forget to release , Will cause memory leaks .

What is memory leak ？

If an object has no reference, it points to , That's the useless object , But for some reason , Not recycled , This is it. Memory leak .

4. Java Automatic memory management for

The automatic garbage collection mechanism makes us Java Programmers do not need to request or free memory , But it also weakens our ability to deal with memory overflow , So it is very important for us to understand the garbage collection mechanism , We can use some monitoring or tuning tools to solve the corresponding problems .

It needs to be emphasized here ,GC and OOM Only in heap space and method area , There is no mandatory regulation on garbage collection in the method area , There are some JVM In fact, there is no garbage collection in the method area , But our default HotSpot There will still be .

Garbage recycling focuses on the new generation , Less collected in the old age , Almost immovable method area , Remember ！！！