The Java Runtime Environment and the JDK Java compiler use the CLASSPATH environment variable to locate classes referenced within Java code. A CLASSPATH variable provides the link between Java code and the actual file path or URL location of the classes being referenced. For example, import java.io.* allows all the classes in the java.io package to be referenced without a fully qualified name. Only the class name is required in the following Java code to use classes from the java.io package. The CLASSPATH environment variable on the system where the Java class declaration is to be compiled must include the location of the Java directory, the root of the java.io package.

 CLASSPATH used to install classes

INSTALL JAVA NEW
FROM FILE 'Invoice.class';