Java™ Application Development on Linux - Dator

168Chapter 6The IBM Developer Kit for Linux, Java 2 Technology Edition6.2USE LINUX FEATURES TO MAKE MULTIPLE JAVA SDKSPLAY NICELY TOGETHERWe did not spend much time discussing the installation of Java on your Linuxsystem in previous chapter. In fact, we did not discuss it at all. This is becausethe installation instructions that come with the SDK are more than adequateif you wish only to install a single Java SDK. But what if you want to install,say, both the Sun Java SDK and the IBM Java SDK? Then things get a bit moreinteresting.We’re going to review the concept of filesystem links, and how they workon Linux. While it may seem odd to discuss them here, we’ll be using links toswitch gracefully between different Java installations. Links are a powerfulfeature in Linux filesystems, and switching SDKs is a good application thereof.If you’re already familiar with links, skip ahead to Section 6.2.2.6.2.1 LinksA link is simply a name attached to a collection of data—that is, to a file. Inother words, every file has one set of data and at least one link (a name). But afile may have more than one link. In other words, two different filenames maypoint to the same data. When you do this, you appear to have two copies ofthe file, but a change to one also changes the other. Deleting one, however,does not delete the other. It merely deletes the link. The file itself is onlydeleted when the last link is gone.6.2.1.1 Hard LinksLinks come in two flavors: hard and symbolic. A hard link looks like a file inand of itself. Let’s show you a hard link, before and after.$ ls -latotal 12drwxrwxr-x 2 mschwarz mschwarz 4096 Jul 8 10:11 .drwx------ 50 mschwarz mschwarz 4096 Jul 8 10:11 ..-rw-rw-r-- 1 mschwarz mschwarz 45 Jul 8 10:11 sample$ cat sampleThis is a samplefile to demonstratelinks.$