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Message:

: c08:controller:Controller.java (Thinking in Java)

Posted by Ivan Villanueva on January 22, 2001 at 9:24 AM

In the example of the Book "Thinking in Java 2", in the chapter 8, ": c08:controller:Controller.java", I don't understand the line "if((next == (start + 1) % events.length) $$ looped) return null;" in the programm.
I think that if "start == next" in the loop, the list is empty and we don't need to write that line, isn't it?

Here the programm:

//: c08:controller:Controller.java
// From 'Thinking in Java, 2nd ed.' by Bruce Eckel
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
// Along with Event, the generic
// framework for all control systems:
package c08.controller;

// This is just a way to hold Event objects.
class EventSet {
private Event[] events = new Event[100];
private int index = 0;
private int next = 0;
public void add(Event e) {
if(index >= events.length)
return; // (In real life, throw exception)
events[index++] = e;
}
public Event getNext() {
boolean looped = false;
int start = next;
do {
next = (next + 1) % events.length;
// See if it has looped to the beginning:
if(start == next) looped = true;
// If it loops past start, the list
// is empty:
if((next == (start + 1) % events.length)
&& looped)
return null;
} while(events[next] == null);
return events[next];
}
public void removeCurrent() {
events[next] = null;
}
}

public class Controller {
private EventSet es = new EventSet();
public void addEvent(Event c) { es.add(c); }
public void run() {
Event e;
while((e = es.getNext()) != null) {
if(e.ready()) {
e.action();
System.out.println(e.description());
es.removeCurrent();
}
}
}
} ///:~