ClearScreen.java

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;

/*
 * Clear console, i.e., push any existing content out of viewport.
 *
 * Command usage is static call:
 *
 * ClearScreen      uses default value of lineFeeds, if default process
 *                  of clearing screen is required
 *
 * ClearScreen n    overrides default value of lineFeeds to integer n to
 *                  be used in case that default process of clearing screen
 *                  is required
 *
 * @author: richarduie [at] yahoo [dot] com
 */

public class ClearScreen {
    // system (OS) specific command to clear console - initialize to
    // default for Mac and Linux
    private static String clearCmd = "clear";

    // default number of line-feeds for brute-force screen-clearing
    // process of defaultClear() method
    private static int lineFeeds = 50;

    // args[0]...optional integer value to replace lineFeeds, in case
    //           caller prefers some other number for default process
    public static void main(String[] args) {
        // reset from default, if argument given
        if (0 < args.length) setLineFeeds( args[ 0 ] );

        setClearCmd();  // set needed command by OS

        // if command could not be identified, use default process...
        if ( "default".equals( clearCmd ) ) defaultClear();
        // ...otherwise execute command
        else {
            try {
                // for read/write of stdout for command process
                String str;
                // execute command - will run in separate, external
                // process not directly impacting current console
                Process p = Runtime.getRuntime().exec( clearCmd );
                // read in process output associated with command
                BufferedReader in = new BufferedReader(
                    new InputStreamReader( p.getInputStream( ) )
                );
                // write each line of external command process to
                // current console
                while ( null != (str = in.readLine( ))) {
                    System.out.println( str );
                }
            }
            catch (IOException e) {
                defaultClear();
            }
        }
    }

    // for any console, assume entering lineFeed newlines pushes
    // existing content above top of viewport (brute-force approach)
    private static void defaultClear() {
        for (int i = 0; i < lineFeeds; i++) {
            System.out.print("\n");
        }
    }
    private static void setLineFeeds( String n ) {
        // attempt to reset lineFeeds from call argument
        try {
            lineFeeds = Integer.parseInt( n );
        }
        catch (NumberFormatException e) {
            // nothing to do - can't remedy caller's failure to provide
            // valid integer input; eat exception and leave default value
            // of lineFeeds unchanged as best guess
            ;   // intentionally empty statement
        }
    }
    // by detected OS, determine needed command
    private static String setClearCmd() {
        String osName = System.getProperty("os.name").toLowerCase();
        boolean isWin = -1 != osName.indexOf( "win" );
        boolean isMac = -1 != osName.indexOf( "mac" );
        boolean isLin = -1 != osName.indexOf( "linux" );
        if (!( isWin || isMac || isLin) ) clearCmd = "default";
        else if (isWin) clearCmd = "cls";
        return clearCmd;
    }
}