Added MessageIdGenerator for providing unique message IDs in the future.

src/main/java/envoy/data/MessageIdGenerator.java

@@ -0,0 +1,41 @@
+package envoy.data;
+
+/**
+ * Generates increasing IDs between two numbers.<br>
+ * <br>
+ * Project: <strong>envoy-common</strong><br>
+ * File: <strong>MessageIdGenerator.java</strong><br>
+ * Created: <strong>31.12.2019</strong><br>
+ * 
+ * @author Kai S. K. Engelbart
+ * @since Envoy Common v0.2-alpha
+ */
+public class MessageIdGenerator {
+
+	private final long	end;
+	private long		current;
+
+	/**
+	 * Creates an instance of {@link MessageIdGenerator}.
+	 *
+	 * @param begin the first ID
+	 * @param end   the last ID
+	 */
+	public MessageIdGenerator(long begin, long end) {
+		current		= begin;
+		this.end	= end;
+	}
+
+	/**
+	 * @return {@code true} if there are unused IDs remaining
+	 */
+	public boolean hasNext() { return current < end; }
+
+	/**
+	 * @return the next ID
+	 */
+	public long next() {
+		if (!hasNext()) throw new IllegalStateException("All IDs have been used");
+		return current++;
+	}
+}