Java™ Application Development on Linux - Dator

8.2 Source Control: Whys and Hows193Kwan goes to commit his modified version of Account.java to the repository,he is notified that Account.java has been changed since his copy was checkedout, and the commit attempt fails. So Kwan does an update which merges the1.8 version of Account.java in with his modified 1.7 version. If all goes well,the resulting file will be a 1.8 version of Account.java which includes Kwan’snew changes in the right place(s). Kwan just commits this to the repository,and Account.java then stands at version 1.9.Note that cautionary phrase “if all goes well.” The merge will work if Tiand Kwan have each modified different parts of the same file. If all Kwan didwas add a new method, it would merge just fine. But what if they both makechanges in the same region of the source file? It is up to the programmer toresolve such conflicts and commit the source once again.In such a situation, CVS does what it can to help out. There is an exampleof a merge conflict later in this chapter. But such conflicts require humanintervention.Merging of conflicts is, undoubtedly, a very manual process, but you willbe surprised by how infrequently you need to do this. Most changes will bemerged clean with no manual intervention required. That’s probably becausemost often, when two or more programmers are modifying the same file, theyare modifying different sections of it.With merging, you have the ability to incorporate other developer’schanges into your version of the source without the fear of losing your changes.No one’s changes get lost, no one’s files get “stepped on.”8.2.1 SetupBefore you can use CVS to track your sources, you need to initialize a repository.You can use this repository for several different projects, so you only needto do this setup once.There are two different ways to connect to a repository—directly on afilesystem, or indirectly over a network. We will use the simpler filesystemmechanism for this discussion. The network connections are described in thereferences at the end of this chapter.In order for CVS to know where the repository is located and how toconnect to it, it looks for an environment variable called CVSROOT. You canassign a value to CVSROOT from the command line each time you create a CVSproject, or for more convenience, you can set it in the shell startup script(e.g., .bashrc) so that its ready all the time. The CVSROOT value is really only