Question

It’s quite often to see com.* package namespace. What does ‘com’ mean? Thanks.

Answer 1

The naming convention for packages is specified in the JLS. Here is the relevant snippet (there’s a lot more in the section):

JLS 7.7 Unique Package Names

You form a unique package name by first having (or belonging to an organization that has) an Internet domain name, such as sun.com. You then reverse this name, component by component, to obtain, in this example, com.sun, and use this as a prefix for your package names, using a convention developed within your organization to further administer package names.

It’s also given in Naming Conventions section of Sun’s code conventions document:

Packages: The prefix of a unique package name is always written in all-lowercase ASCII letters and should be one of the top-level domain names, currently com, edu, gov, mil, net, org, or one of the English two-letter codes identifying countries as specified in ISO Standard 3166, 1981.

Subsequent components of the package name vary according to an organization’s own internal naming conventions. Such conventions might specify that certain directory name components be division, department, project, machine, or login names.

Examples: com.sun.eng, com.apple.quicktime.v2, edu.cmu.cs.bovik.cheese

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So com. prefix in package names means the same as .com suffix in domain names: "commercial".