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+Implement a class `Exchanger<T>` that is usable to exchange an object
+of type `T` between exactly two threads:
+
+```java
+class Exchanger<T> {
+	// your task
+	T exchange(T s) {
+		// your task
+	}
+}
+```
+
+Every thread invokes method `exchange()` with the object it wants to pass to the other thread and
+receives as the result of that invocation the object that the other thread has passed. Make sure that
+your code works even when both threads happen to pass the same object.
+
+Initially, your Exchanger should be usable for a single exchange only. Then, add functionality to make
+it usable repeatedly by the same two threads. In a third step, extend your class to make it usable by
+any number of threads: Each time, the "next two" threads perform an exchange among each other;
+note that in this scenario it may happen that a thread uses an exchanger where the previous exchange
+has not yet finished.
+
+In the source code folder on the server you'll find a class `ExchangerTester` that tests your
+`Exchanger` (only for a single exchange; you can extend it yourself so as to test a series of exchanges).
+The output of that program should look as follows:
+
+```
+	Main thread received World in exchange for Hello
+	2nd thread received Hello in exchange for World
+	2nd thread received 2337 in exchange for 2337
+	Main thread received 2337 in exchange for 2337
+```