import java.util.Timer;

import java.util.TimerTask;

/**

* Repeatedly move an asterisk forward 20 steps and then backward 20 steps.

*/

public class BackAndForth{

private static final long INTERVAL = 500;

private static final String TOKEN = "*";

private static int MAX_STEP = 20;

private static volatile int stepCount = 0;

private static volatile boolean isForward = true;

public static void main(String[] args){

Timer timer = new Timer();

TimerTask task = new TimerTask(){

@Override

public void run(){

StringBuilder sb = new StringBuilder(TOKEN);

for(int i=0; i<stepCount; i++){

sb.insert(0, " ");

}

System.out.println(sb.toString());

if(isForward){

stepCount++;

}else{

stepCount--;

}

if(stepCount == MAX_STEP){

isForward = false;

}else if(stepCount == 0){

isForward = true;

}

}

};

long interval = -1;

if(args.length!=0){

try{

interval = Long.parseLong(args[0]);

}catch(NumberFormatException nfe){

nfe.printStackTrace();

}

}

if(interval < 0){

interval = INTERVAL;

}

timer.schedule(task, 1000, interval);

}

}