added ex S1

src/exercises/ex_s1/Cow.java

@@ -0,0 +1,33 @@
+package exercises.ex_s1;
+
+import java.util.Random;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class Cow implements Runnable {
+    private String name;
+    private ConcurrentHashMap<String, Integer> stalls;
+    private final Random random = new Random();
+
+    public Cow(String name, ConcurrentHashMap<String, Integer> stalls) {
+        this.name = name;
+        this.stalls = stalls;
+    }
+
+    @Override
+    public void run() {
+        while (true) {
+            try {
+                Thread.sleep((long) (1000L + Math.random() * 5000L));
+            } catch (InterruptedException e) {
+                break;
+            }
+            String key = "box" + random.nextInt(1, 4);
+            Integer units = stalls.replace(key, 0);
+            if (units == null || units == 0) {
+                System.out.println(name + " ate nothing");
+            } else {
+                System.out.println(name + " ate " + units + " units of food from " + key);
+            }
+        }
+    }
+}

src/exercises/ex_s1/Farmer.java

@@ -0,0 +1,30 @@
+package exercises.ex_s1;
+
+import java.util.Random;
+import java.util.concurrent.ConcurrentHashMap;
+
+public class Farmer implements Runnable {
+    private String name;
+    private ConcurrentHashMap<String, Integer> stalls;
+    private final Random random = new Random();
+
+    public Farmer(String name, ConcurrentHashMap<String, Integer> stalls) {
+        this.name = name;
+        this.stalls = stalls;
+    }
+
+    @Override
+    public void run() {
+        while (true) {
+            try {
+                Thread.sleep((long) (1000L + Math.random() * 2000L));
+            } catch (InterruptedException e) {
+                break;
+            }
+            String key = "box" + random.nextInt(1, 4);
+            int units = random.nextInt(10, 100);
+            stalls.put(key, units);
+            System.out.println(name + " puts " + units + " units of food in " + key);
+        }
+    }
+}

src/exercises/ex_s1/TestingConcurrentHashMap_Farm.java

@@ -0,0 +1,14 @@
+package exercises.ex_s1;
+
+import java.util.concurrent.ConcurrentHashMap;
+
+public class TestingConcurrentHashMap_Farm {
+    public static void main(String[] args) {
+        ConcurrentHashMap<String, Integer> animalStallMap = new ConcurrentHashMap<>();
+        new Thread(new Farmer("Verena", animalStallMap)).start();
+        new Thread(new Farmer("Pierre", animalStallMap)).start();
+        for (int i = 1; i < 10; i++) {
+            new Thread(new Cow("Cow" + i, animalStallMap)).start();
+        }
+    }
+}