About ClassLoader

All three default classloaders follow the delegation model. Before a child classloader tries to locate a class, it delegates that task to a parent. When your application requests a particular class, the application classloader delegates this request to the extension classloader, which in turn delegates it to the bootstrap classloader. If the class that you requested is a Java core class, the bootstrap classloader will make the class available to you. However, if it cannot find the class, the request returns to the extension classloader, and from there to the application classloader itself. The idea is that each classloader first looks up to its parent for a particular class. Only if the parent does not have the class does the child classloader try to look it up itself.

About Memory

Each instance of a JVM has one method area and a heap. These areas are shared by all threads running within the instance.
The information regarding the type is loaded from the class files when the JVM loads a class file. This information is stored in the method area. All the objects which are instantiated placed on the heap.
As each new thread is created, it is assigned its own pc register(program counter) and java stack. If the thread is executing a java method (not a native method), the counter in the pc register points to the next instruction to execute. The java stack comprises of frames. A frame consists of the state of one method invocation. When a thread invokes a method, a new frame is pushed on the thread’s stack. On completion of the method execution, the VM pops and discards the frame. No other thread can access another threads pc register or java stack.