Java class loading
The JVM (Java Virtual Machine) will load classes as and when the classes are required (this is called lazy-loading). Locations of the classes to be used are specified in three places:-
jre/lib/ext/)Classes are loaded using classes that are subtypes of java.lang.ClassLoader. This described in a more detail in this Topic: Classloaders.
Classpath
The classpath is a parameter used by the JVM or compiler which specifies the locations of user-defined classes and packages.
This can be set in the command line as with most of these examples or through an environmental variable (CLASSPATH)