Note that the javac command requires a filename (or multiple source files separated by spaces), whereas the java command requires a single class name. We run the program using the java command, which displays the output on the following line. Running ls again, we see that the compiler generated a new file, Hello.class, which contains the byte code. 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 ( java).įigure A.3 shows an example where the Hello.java source file is stored in the Desktop directory.Īfter changing to that location and listing the files, we use the javac command to compile Hello.java. There are many good tutorials online for learning the command line for your operating system just search the web for “command line tutorial”. Many advanced tools, both for software development and general purpose computing, are available only at the command line. It allows you to run programs, manage files and directories, and monitor system resources. The command line is a direct interface to the operating system. One of the most powerful and useful skills you can learn is how to use the command-line interface, also called the “terminal”. What’s nice about this feature is that you don’t have to create a new class, declare a main method, write arbitrary expressions inside statements, save the source file, and get all of your code to compile in advance.Īlso, you can press the up/down arrows on the keyboard to repeat previous commands and experiment with incremental differences. This feature saves you from having to type every time. Notice in Figure A.2 how the variable declarations end with semicolons, but the logic expressions in the following lines do not. If you don’t end an expression (or statement) with a semicolon, DrJava automatically displays its value. There is one subtle detail to note when using the Interactions feature. Refer to the DrJava documentation ( ) for more details. Simply double-click the JAR file to run DrJava. We recommend that you save it to your Desktop or another convenient location. To install DrJava, visit and download the JAR file. Then accept the license agreement and select the installer for your operating system.ĭon’t forget to run the installer after you download it! Scroll down to “Java Platform, Standard Edition” and click the download button under JDK. To install the JDK, search the web for “download JDK” which should take you to Oracle’s website. The IDE we recommend is DrJava, which is an open-source development environment written in Java (see Figure A.1). The JDK we recommend is Java SE (Standard Edition), which Oracle makes available for free. A simple text editor such as Notepad++ or Sublime Text, and/or an IDE such as DrJava, Eclipse, jGrasp, or NetBeans.The Java Development Kit (JDK), which includes the compiler, the Java Virtual Machine (JVM) that interprets the compiled byte code, and other tools such as Javadoc.If you are unable to install software on your computer (which is often the case in public schools and Internet cafés), you can use these online development environments for almost everything in this book.īut if you want to compile and run Java programs on your own computer, you will need: The easiest way to start programming in Java is to use a website that compiles and runs Java code in the browser.Įxamples include, ,, and others. Instead, we provide this appendix with a brief introduction to DrJava – an integrated development environment (IDE) that is well suited for beginners – and other development tools, including Checkstyle for code quality and JUnit for testing. We avoided putting these details in the main text, because they can be distracting. The steps for compiling, running, and debugging Java code depend on your development environment and operating system. You might prefer to read the PDF version, or you can buy a hardcopy at In particular, some of the symbols are not rendered correctly. This HTML version of Think Java is provided for convenience, but it is not the best format of the book.
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