How to Include JAR Files in the Classpath for Java Compilation (javac and apt)?

Including Jars in Classpath on Command Line (javac or apt)

To compile Java programs that rely on external libraries, these libraries must be included in the classpath. This article explores how to incorporate jars into the classpath using command-line options for javac or apt.

javac

For javac, use the -cp option followed by a colon-separated list of directories and jar files. For example, to compile HelloImp.java with the jsr181-api.jar library:

javac -cp .:jsr181-api.jar HelloImp.java

apt

apt also supports -cp to set the classpath. However, it recommends using the -module-path option for modular Java applications. For example:

apt -module-path .:jsr181-api jar HelloImp

Temporary Inclusion

If you prefer not to permanently modify your command-line arguments, you can use the java command with the -cp option:

java -cp .:jsr181-api.jar HelloImp

This will set the classpath temporarily for the duration of the command.

Manifest Text File

The manifest text file approach can be more versatile. Create a manifest file named MANIFEST.MF with the following content:

Manifest-Version: 1.0
Class-Path: jsr181-api.jar

Then, compile the program with:

javac HelloImp.java -m MANIFEST.MF

Additional Notes

• Ensure the correct directory separators are used, depending on your operating system (':' for Linux/macOS, ';' for Windows).
• Add the current working directory (.) to the classpath to access files in the current folder.
• When using multiple jars, ensure they are all available in the specified order.

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