finished ex Z4

src/exercises/ex_z4/Bidder.java

@@ -30,16 +30,27 @@ public class Bidder implements Runnable {
             if (state == BIDDING) {
                 Random rand = new Random();
                 double addon = rand.nextDouble(500);
-                double base = auctioneer.getMaximumBid().amount();
+                Bid maximumBid = auctioneer.getMaximumBid();
+                double base = maximumBid == null ? 0 : maximumBid.amount();
                 lastBid = base + addon;
                 auctioneer.placeBid(new Bid(this, lastBid));
+                long minSleep = (long) (base * 10);
                 try {
-                    Utils.randomSleep(100, 5000);
+                    Utils.randomSleep(minSleep, minSleep + 1000);
                 } catch (InterruptedException e) {
                     throw new RuntimeException(e);
                 }
             } else if (state == FINISHED) {
                 break;
+            } else {
+                auctioneer.stateLock.lock();
+                try {
+                    auctioneer.stateCond.await();
+                } catch (InterruptedException e) {
+                    throw new RuntimeException(e);
+                } finally {
+                    auctioneer.stateLock.unlock();
+                }
             }
         }
     }