law(pingpong,language(java))

public class Pingpong extends Law {

    public void sent(String source, String message, String dest) {
        String pingToY = "pingTo(" + dest + ")";
        String pingFromY = "pingFrom(" + dest + ")";

        if (message.startsWith("ping(") && !CS.has(pingToY)) {
            doAdd(pingToY); 
	    doForward();
        }
        if (message.startsWith("pong(") && CS.has(pingFromY)) {
            doRemove(pingFromY);
	    doForward();
        }
    }

    public void arrived(String source, String message, String dest) {
        if (message.startsWith("ping(")) {
            doAdd("pingFrom(" + source + ")");
            doDeliver();
        }
        if (message.startsWith("pong(")) {
            doRemove("pingTo(" + source + ")");
            doDeliver();
        } 
    }

    public void disconnected() {
	doQuit();

    }
}