PATH

CLASSPATH

used by operating system to locate JDK binaries like “java” or “javac”

used by Application ClassLoader to locate and load compile Java bytecodes stored in the .class file

cannot be overridden by any Java settings

can be overridden by providing command line option -classpath or -cp to both “java” and “javac” commands or by using Class-Path attribute in Manifest file inside JAR archive