JVM(Java Virtual Machine) acts as a run-time engine to run Java applications. JVM is the one that actually calls the main method present in a java code. JVM is a part of JRE(Java Runtime Environment).
Java applications are called WORA (Write Once Run Anywhere). This means a programmer can develop Java code on one system and can expect it to run on any other Java-enabled system without any adjustment. This is all possible because of JVM.
When we compile a .java file, .class files(contains byte-code) with the same class names present in .java file are generated by the Java compiler. This .class file goes into various steps when we run it. These steps together describe the whole JVM.
Class Loader Subsystem
It is mainly responsible for three activities.
1. Loading
2. Linking
3. Initialization
Loading: The Class loader reads the “.class” file, generate the corresponding binary data and save it in the method area. For each “.class” file, JVM stores the following information in the method area.
The fully qualified name of the loaded class and its immediate parent class.
Whether the “.class” file is related to Class or Interface or Enum.
Modifier, Variables and Method information etc.
After loading the “.class” file, JVM creates an object of type Class to represent this file in the heap memory. Please note that this object is of type Class predefined in java.lang package. These Class object can be used by the programmer for getting class level information like the name of the class, parent name, methods and variable information etc. To get this object reference we can use getClass() method of Object class.