How does java permanate generation & young generation work?

Java Stacks or Frames

Java stacks are created private to a thread. Every thread will have a program counter (PC) and a java stack. PC will use the java stack to store the intermediate values, dynamic linking, return values for methods and dispatch exceptions. This is used in the place of registers.

Memory Generations

HotSpot VM’s garbage collector uses generational garbage collection. It separates the JVM’s memory into and they are called young generation and old generation.

Young Generation

Young generation memory consists of two parts, Eden space and survivor space. Shortlived objects will be available in Eden space. Every object starts its life from Eden space. When GC happens, if an object is still alive and it will be moved to survivor space and other dereferenced objects will be removed.

Old Generation – Tenured and PermGen

Old generation memory has two parts, tenured generation and permanent generation (PermGen). PermGen is a popular term. We used to error like PermGen space not sufficient.

GC moves live objects from survivor space to tenured generation. The permanent generation contains meta data of the virtual machine, class and method objects.