JVM Heap, GC (Garbage Collection)

1. JVM Heap

JVM Heap is the Memory area where Objects (Instances) allocated mainly through the new syntax are located. The JVM Heap is divided into three areas: Young Generation, Old Generation, and Permanent. The Young Generation is the area where recently created Objects are located, and the Old Generation is the area where Objects that have survived multiple GC operations after creation are located. The Permanent area is the space where Static Objects, String Objects, Class Meta, Method Meta, and JIT Meta information are stored. The Permanent area is not subject to GC. In addition, since the Permanent area does not exist in Java 8, this article does not cover it in detail.

[Figure 2] shows the Options related to the JVM Heap. The size of each area can be configured in various ways through these options. -Xms means the Heap Size at JVM startup, and -Xmx means the maximum Heap Size.

2. Garbage Collector

2.1. Serial, Parallel, CMS

2.2. G1

3. Object Reachability

4. References

Java Garbage Collection (NAVER D2) : http://d2.naver.com/helloworld/1329
Java Reference and GC (NAVER D2) : http://d2.naver.com/helloworld/329631
Java 8 Perm : https://yckwon2nd.blogspot.kr/2015/03/java8-permanent.html
G1 : http://www.oracle.com/technetwork/tutorials/tutorials-1876574.html

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