What is class loader in Java..?

part of the Java Runtime Environment that dynamically loads Java classes into the Java Virtual Machine

the concept  of class loader describes the behavior of converting class (ie. Class S) into the bits which are responsible of implementing that Class.

the Java run time does not need to know anything about files and file systems when running Java programs because of the existance of this concept

class loader load .class file into method area

The javaclass loader is a part of the java runtime environment that dynamically loads java classes into the java virtual machine. usually classes are only loaded on demand. the java runtime system does not need to know about files and file systems because of class loaders. 

Java ClassLoader is a part of JRE that dynamically loads the Java classes into JVM

Calss loader in java is a part of JRE ( Java Runtiem Environemnt) that laods java classes into JVM ( Java Virtual Machine). it is the responsible to locate the libarireis, reads the content and load them.