Java Memory Basic

最新推荐文章于 2025-08-11 20:54:36 发布

weixin_30624825

最新推荐文章于 2025-08-11 20:54:36 发布

阅读量58

点赞数

CC 4.0 BY-SA版权

文章标签： java

原文链接：http://www.cnblogs.com/reynold-lei/p/3422531.html

本文详细介绍了 HotSpot 虚拟机的垃圾回收机制，包括新生代和老年代的划分，以及 Eden 和 Survivor 空间的运作方式。解释了对象如何在这些区域间移动，何时触发 Minor GC 和 Full GC，并讨论了垃圾收集过程中的性能考量。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

转自： http://www.blogjava.net/justinchen/archive/2009/justinchen/archive/2009/01/08/248738.html

GC and Full GC

The garbage collector (GC) detects garbage, defined as objects that are no longer reachable, then reclaims it and makes space available to the running program. The GC typically works in a stop-the-world fashion -- that is, it freezes the heap when working.

The above diagram describes the layout of HotSpot VM Heap and it consists of three parts: perm generation, old generation and new/yang generation. The perm generation is basically for class loading. Next are the old and young generation. The young generation is further broken up into three spaces: Eden, Survivor Space 1 (SS#1) and Survivor Space 2 (SS#2).

Garbage Collection1. When you have a new object, the object gets created in Eden space.
2. So after running for a while, Eden space will fill up.a minor garbage collection occurs, in which all the objects alive in Eden are copied over to SS#1. Eden is then empty and ready to receive new objects.
3. After the minor GC, objects are allocated to Eden again. After a time, the Eden space fills up again, and another minor GC occurs. The objects surviving in SS#1 and Eden are copied to SS#2, and both SS#1 and Eden are reset. Although objects are frequently recopied, either from Eden or from one SS to another, at any one time, only Eden and one SS are operating.
4. Every time an object moves from Eden to SS or from one SS to another, a counter and its header is incremented. By default, if the copying occurs 16 times or more, the HotSpot VM stops copying them and moves them to the old generation.
5. If an object can't be created in Eden, it goes directly to the old generation. Moving an object from SS to the old generation because of its age is called tenuring. Because of tenuring, the old generation becomes full over time. This calls for garbage collection of the old generation, which is called a full GC. A full GC is a compaction process that is slower than a minor GC.

转载于:https://www.cnblogs.com/reynold-lei/p/3422531.html