The Java compiler expects its input from files whose names end in .java . Table 3.2 has some of the common suffixes. Note that, unlike in some other operating systems, Unix does not care what your file is called, and what suffix it has. Many programs, however, do expect certain suffixes. The file system separates users' files using a concept called directories .
Directories are special files that can contain both files and more directories.
Each user on the system has a home directory in which they may create files and directories. Similarly, each child directory cha contain other files and also other child directories. Because they are hierarchically organized, directories provide a logical way to organize files.