- Java Virtual Machine
1) JVM?
Method area : All class level information like class name, immediate parent class name, methods and variables information are stored, including static variables. There is only one method area per JVM, and it is a shared resource.
Heap area :Information of all objects is stored in heap area. There is also one Heap Area per JVM. It is also a shared resource.
Stack area :For every thread, JVM create one run-time stack which is stored here. Every block of this stack is called activation record/stack frame which store methods calls. All local variables of that method are stored in their corresponding frame. After a thread terminate, it’s run-time stack will be destroyed by JVM. It is not a shared resource.
PC Registers :Store address of current execution instruction of a thread. Obviously each thread has separate PC Registers.
Native method stacks :For every thread, separate native stack is created. It stores native method information.
2) Class Loaders ?
Bootstrap class loader : It loads core java API classes present in JAVA_HOME/jre/lib directory. This path is popularly known as bootstrap path. It is implemented in native languages like C, C++.
Extension class loader : It is child of bootstrap class loader. It loads the classes present in the extensions directories JAVA_HOME/jre/lib/ext(Extension path) or any other directory specified by the java.ext.dirs system property. It is implemented in java by the sun.misc.Launcher$ExtClassLoader class.
System/Application class loader : It is child of extension class loader. It is responsible to load classes from application class path. It internally uses Environment Variable which mapped to java.class.path. It is also implemented in Java by the sun.misc.Launcher$AppClassLoader class.
