How to load classes at runtime from a folder or Java package

Using CLASSPATH, you can load any classes at runtime.

Like the .java source files, the compiled .class files should be in a series of directories that reflect the package name. However, the path to the .class files does not have to be the same as the path to the .java source files. You can arrange your source and class directories separately, as −

<path-one>\sources\com\apple\computers\Dell.java
<path-two>\classes\com\apple\computers\Dell.class

By doing this, it is possible to give access to the classes directory to other programmers without revealing your sources. You also need to manage source and class files in this manner so that the compiler and the Java Virtual Machine (JVM) can find all the types your program uses.

The full path to the classes directory, \classes, is called the classpath and is set with the CLASSPATH system variable. Both the compiler and the JVM construct the path to your .class files by adding the package name to the classpath.

Say \classes is the class path, and the package name is com.apple.computers, then the compiler and JVM will look for .class files in \classes\com\apple\computers.

A classpath may include several paths. Multiple paths should be separated by a semicolon (Windows) or colon (Unix). By default, the compiler and the JVM search the current directory and the JAR file containing the Java platform classes so that these directories are automatically in the classpath.