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The Java Compiler & Interpreter
Java Development Kit
The Java Development Kit has been installed on the class server. It contains a variety of tools and Java development information. The following list indicates the main components of the JDK:- Runtime interpreter
- Compiler
- Applet viewer
- Debugger
- Class file disassembler
- Header and stub file generator
- Documentation generator
- Archiver
- Digital signer
- Remote Method Invocation tools
- Sample demos and source code
- API source code
Compiling Your Program
The Java compiler (javac) is used to compile Java source code files into executable Java bytecode classes. In Java, source code files have the extension .java. The Java compiler takes files with this extension and generates executable class files with the .class extension. The compiler creates one class file for each class defined in a source file. This means that it is possible for a single Java source code file to compile into multiple executable class files. When this happens, it means that the source file contains multiple class definitions.Even though Java source files and classes are typically given the extensions .java and .class, it is important to note that some operating systems are not capable of fully representing these extensions because of their length. For example, Windows 3.1 is limited to three-character extensions, so Java source files and classes must use the extensions .jav and .cla.
The Java compiler is a command-line utility that works in a manner similar to the Java runtime interpreter. The syntax for the Java compiler follows:
javac Options SourceFilename.extensionThe Filename argument specifies the name of the source code file you want to compile. The Options argument specifies options related to how the compiler creates the executable Java classes. To compile the program which calculates the area of a circle, we would use the folloeing command:
javac CircleThree.javaThis would create a file named CircleThree.class which can then be run using the Java interpreter.
The table below lists the command line options that are available for the Java compiler.
| Option | Description |
| -classpath path | Determines the path in which the compiler looks for classes. |
| -d directory | Determines the directory in which javac stores the output files. |
| -deprecation | Provides details about program statements and objects which have been deprecated in newer standards. |
| -g | Tells javac to create debugging information, which is used by debugging tools. |
| -nowarn | Tells javac not to display warnings as it compiles a file. |
| -O | Tells java to optimize the compiled program. |
| -verbose | Tells javac to display status information as it works. |
Running Your Program
The Java runtime interpreter (java) is used to run standalone Java executable programs in compiled, bytecode format. The runtime interpreter acts as a command-line tool for running Java programs that are either nongraphical or that manage their own window frame (applications); graphical programs requiring the display support of a Web browser (applets) are executed entirely within a browser. The syntax for using the runtime interpreter is illustrated below:java Options ClassName ArgumentsThe ClassName argument specifies the filename of the class you want to execute. If the class resides in a package, you must fully qualify the name. For example, if you want to run a class called Circle that is located in a package called FindArea, you execute it in the interpreter as follows:
java FindArea.CircleWhen the Java interpreter executes a class, what it is really doing is executing the main() method of the class. The interpreter exits when the main() method and any threads created by it are finished executing. You need not worry if you are not yet familiar with the main() method or Java threads ... they are not critical to understanding the runtime interpreter at this point. The main() method accepts a list of arguments that can be used to control the program. The Arguments argument to the interpreter specifies the arguments passed into the main() method. For example, if you have a Java class called TextFormater that performs some kind of formating on a text file, you would likely pass the name of the file as an argument, like this:
java TextFormater MyFile.txtThe Options argument specifies options related to how the runtime interpreter executes the Java program. Please refer to the JDK documentation for more information about the options supported in the runtime interpreter.
