classpaths

Classpaths (or the Java classpath) are a mechanism used by the Java platform and other JVM-based environments to locate class files and libraries at runtime. A classpath is a list of file system locations and archives, such as directories and JAR or ZIP files. The runtime searches these locations in a defined order to find a requested class or resource.

The classpath can be specified in several ways: via the CLASSPATH environment variable, or via the -cp (or -classpath) option passed to the java launcher. For compilation, javac also accepts -cp. The current directory is included by default if no classpath is specified. The path separator is a semicolon on Windows and a colon on Unix-like systems. Each entry may point to a directory containing package subdirectories or to a JAR/ZIP file; a JAR may contribute a manifest Class-Path entry that further extends the effective classpath.

Class loading in the JVM uses a parent-first delegation model. When a class is requested, the loader searches the classpath entries in order, stopping at the first match. Since modern Java supports modules, there is also a module path for modular applications; the classpath remains relevant for legacy and non-modular code.

Practical notes: avoid over-reliance on a global CLASSPATH; use -cp in scripts for reproducible builds. Quotes may be needed to handle spaces. Common examples show different separators for Windows and Unix. The System.getProperty("java.class.path") can reveal the current classpath, and -verbose:class can trace loaded classes.