Introduced in Java 5, pack200 was a compression scheme for JAR files. It was used to decrease the disk space and bandwidth demand when Java programs were packaged, transmitted, or delivered. Developers used pack200 and unpack200 to compress and decompress the Java JAR files.

However, these are becoming irrelevant in today's modern storage and transmission improvements. JEP 336 deprecates the pack200 and unpack200 tools, and also the corresponding pack200 API.