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By default, classpath is set to current directory. System/Application ClassLoader: This is the child classloader of Extension classloader.It loades the jar files located inside $JAVA_HOME/jre/lib/ext directory. Extension ClassLoader: This is the child classloader of Bootstrap and parent classloader of System classloader.It loads the rt.jar file which contains all class files of Java Standard Edition like java.lang package classes, package classes, java.util package classes, java.io package classes, java.sql package classes etc.

Bootstrap ClassLoader: This is the first classloader which is the super class of Extension classloader.There are three built-in classloaders in Java. Whenever we run the java program, it is loaded first by the classloader.

It contains classloader, memory area, execution engine etc.Ĭlassloader is a subsystem of JVM which is used to load class files. Let's understand the internal architecture of JVM. Runtime Instance Whenever you write java command on the command prompt to run the java class, an instance of JVM is created.An implementation Its implementation is known as JRE (Java Runtime Environment).

Its implementation has been provided by Oracle and other companies. But implementation provider is independent to choose the algorithm.