Physics Simulation       Lecture 12A Browsers System Properties Cursor Icons MouseButtons Keystrokes Audio Timing Toolkit AppletContext Run Ext. Programs Misc. Tools Lectures 1A: Introduction 1B: Java Intro 2A: BuildingBlocks 2B: Objects 3A: More Objects 3B: Exceptions        & Threads 4A: Waves 4B: Nuclear &        Particle 5A: AWT 5B: More AWT       & Graphics 6A:Detectors &       Simulation 6B: LHC/Atlas &      RandomSims     7A: Swing 7B: Java2D 8A: Java Apps 8B: Dialogs &     MoreClasses 9A: Java I/O 9B: Utilities,         Unicode 10A: More     Threading 10B: File     Handling 11A: Array,Print,     Images 11B: SimplePhysics     Simulation 12A: Tips &     Techniques 12B: More Tips &     Techniques 13A: Satellite     Simulations 13B: Intro to Java     Networking 14A: Java Servers 14B: HTTP Server 15A: ServerClient 15B: ServerClient    Expt.Simulation 16A: Course           Review 16B: ExerciseTest         Discussion     Contacts     Description     Exercises     Index     Outline     Q&A     Resources     StudentInfoForm     Student Pages     What's New

Home : Lectures : Lecture 12A : Running External Programs Running External Programs Applications occasionally need to start other programs. For example, one might want to start a browser. The java.lang.Runtime and java.lang.Process classes are available for executing and communicating with external programs. Here is code to run a MS-DOS batch file that does a directory listing. The program reads the output from this program and prints it out. doDir.bat: dir *.java execDir.java // Modified from Just Java import java.io.*; public class execDir {     public static void main(String args[]) {     try {       Runtime rt = Runtime.getRuntime();       // step 1         Process prcs = rt.exec("doDir.bat");     // step 2       InputStreamReader isr =                  // step 3         new InputStreamReader( prcs.getInputStream() );       BufferedReader br = new BufferedReader(  // step 4.                                         isr );       String line;       while  ((line = br.readLine()) != null)                    System.out.println(line);     } catch(IOException ioe) { System.out.println(ioe); }   } } Note that this obviously involves the details of the particular host platform and OS. For example, the exec method does not use a shell. If a shell is needed, then it can be run directly. Communication can only be via the standard in, out, and err streams.

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