JVM

1. JDK = Java Language + JVM + Java API
JRE = JVM + JAVA SE API

2. 3 famous JVM: HotSpot(Sun), JRocket(BEA), J9(IBM)

3. GC 收集器
Young Generation： Serial， ParNew & Parallel Scavenge
Tenured Generation: Serial Old, Parallel Old & CMS
G1 between Young & Tenured Generation.

4. Heap Space & Non-heap space
Heap Space: Eden Space, Survivor Space & Tenured Space
Non-heap Space: Code Cache, Perm Generation, JVM Stack & Local Method Stack

5. Command Tools
1) jps (JVM Process Status) like linus ps command
2) jstat + -gcutil + vmid
3) jmap (Memory Map for Java）: 获取dump文件，查询finalize执行队列，java Heap & Perm 详细信息
4) jmap -dump:format=b,file=<filename>
jmap -heap +vmid : detail of heap (only availabe in Linux)
jmap -histo +vmid: 显示堆中对象统计信息，包括类，实例数量，合计容量
5) jhat (JVM Heap Analysis Tool): 与jmap搭配使用，分析堆转储快照（html方式）
但现在更常用Eclipse Memory Analyzer, IBM Heap Analyzer.
6) jstack (Statck Trace for Java): 当前线程快照threaddump
jstatck + vmid