cf. http://vimeo.com/24608862 !

Proteus.java

package org.ros.tutorials.pubsub;

import org.apache.commons.logging.Log;
import org.ros.MessageListener;
import org.ros.Node;
import org.ros.NodeConfiguration;
import org.ros.NodeMain;
import org.ros.Subscriber;
import org.ros.Publisher;

import org.ros.message.sensor_msgs.LaserScan;
import org.ros.message.geometry_msgs.Twist;

public class Proteus implements NodeMain {

  @Override
  public void main(NodeConfiguration configuration) {
    Node node = null;
    try {
      node = new Node("test_cmd", configuration);
      final Publisher<Twist> publisher =
          node.createPublisher("/ATRV/Motion_Controller", Twist.class);

      final Log log = node.getLog();
      node.createSubscriber("/ATRV/Sick", new MessageListener<LaserScan>() {
        @Override
        public void onNewMessage(LaserScan msg) {
          int i, mid = msg.ranges.length / 2;
          Twist cmd = new Twist();
          // halt if an object is less than 2m in a 30deg angle
          boolean halt = false;
          for (i = mid - 15; i <= mid + 15; i++) {
            if (msg.ranges[i] < 2.0) {
              halt = true;
              break;
            }
          }
          if (halt) {
            double midA = 0, midB = 0;
            // we go to the highest-range side scanned
            for (i = 0; i < mid; i++)
              midA += msg.ranges[i];
            for (i = mid; i < msg.ranges.length; i++)
              midB += msg.ranges[i];
            log.info("A:" + midA + ", B:" + midB);
            if (midA > midB) {
              cmd.angular.z = -1;
            } else {
              cmd.angular.z = 1;
            }
          } else {
            cmd.linear.x = 1;
          }
          publisher.publish(cmd);
        }
      }, LaserScan.class);
    } catch (Exception e) {
      if (node != null) {
        node.getLog().fatal(e);
      } else {
        e.printStackTrace();
      }
    }
  }
}