One of the most powerful and useful skills you can learn is how to use the command-line interface, also called the “terminal”. The command line is a direct interface to the operating system. It allows you to run programs, manage files and directories, and monitor system resources. Many advanced tools, both for software development and general purpose computing, are available only at the command line.
There are many good tutorials online for learning the command line for your operating system; just search the web for “command line tutorial”. On Unix systems like Linux and OS X, you can get started with just four commands: change the working directory (
cd), list directory contents (
ls), compile Java programs (
javac), and run Java programs (
Figure 15.3.1 shows an example where the
Hello.java source file is stored in the Desktop directory. After changing to that location and listing the files, we use the
javac command to compile
ls again, we see that the compiler generated a new file,
Hello.class, which contains the byte code. We run the program using the
java command, which displays the output on the following line.
Note that the
javac command requires a filename (or multiple source files separated by spaces), whereas the
java command requires a single class name. If you use DrJava, it runs these commands for you behind the scenes and displays the output in the Interactions Pane.
Taking time to learn this efficient and elegant way of interacting with your operating system will make you more productive. People who don’t use the command line don’t know what they’re missing.