diff --git a/app/src/main/java/ch/nuth/zhaw/exbox/CObject.java b/app/src/main/java/ch/nuth/zhaw/exbox/CObject.java
new file mode 100644
index 0000000..1fb7f78
--- /dev/null
+++ b/app/src/main/java/ch/nuth/zhaw/exbox/CObject.java
@@ -0,0 +1,29 @@
+package ch.nuth.zhaw.exbox;
+
+/** base class of collectable objects */
+public class CObject implements Collectable {
+   private boolean mark;  // to mark object
+   public CObject next, down;
+   public String value;
+
+   public CObject (String value) {
+      this.value = value;
+   }
+
+   public void setMark(boolean mark) {
+      this.mark = mark;
+   }
+
+   public boolean isMarked() {
+      return mark;
+   }
+
+   public String toString() {
+     return value;
+   }
+
+   @Override
+   public boolean equals(Object o) {
+      return this.getClass() == o.getClass() && this.value.equals(((CObject)o).value);
+   }
+}
diff --git a/app/src/main/java/ch/nuth/zhaw/exbox/Collectable.java b/app/src/main/java/ch/nuth/zhaw/exbox/Collectable.java
new file mode 100644
index 0000000..944a959
--- /dev/null
+++ b/app/src/main/java/ch/nuth/zhaw/exbox/Collectable.java
@@ -0,0 +1,6 @@
+package ch.nuth.zhaw.exbox;
+
+public interface Collectable {
+   void setMark(boolean b);
+   boolean isMarked();
+}
diff --git a/app/src/main/java/ch/nuth/zhaw/exbox/Storage.java b/app/src/main/java/ch/nuth/zhaw/exbox/Storage.java
new file mode 100644
index 0000000..46a0cf0
--- /dev/null
+++ b/app/src/main/java/ch/nuth/zhaw/exbox/Storage.java
@@ -0,0 +1,188 @@
+package ch.nuth.zhaw.exbox;
+
+import java.lang.reflect.Constructor;
+import java.lang.reflect.Field;
+import java.util.HashMap;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Consumer;
+
+public class Storage {
+    public static boolean generationalGCActive = true; // in Aufgabe 2 verwendet
+    public static StringBuffer log = new StringBuffer();
+    private static List<Collectable> root;
+    private static List<Collectable> youngHeap;
+    private static List<Collectable> oldHeap;
+    public static boolean youngGenerationOnly = true;
+
+    static {
+        clear();
+    }
+
+    public static void clear() {
+        root = new LinkedList<>();
+        youngHeap = new LinkedList<>();
+        // oldHeap erst in Aufgabe 2 verwenden!
+        oldHeap = new LinkedList<>();
+    }
+
+    /* add root object */
+    public static void addRoot(Collectable obj) {
+        root.add(obj);
+    }
+
+    // create a collectable object of class cls
+    public static Collectable _new(String cls, Object arg) {
+        Collectable obj = null;
+        try {
+            // create an object and call constructor
+            Constructor<?> cst = Class.forName(getPackage() + cls).getConstructor(arg.getClass());
+            obj = (Collectable) cst.newInstance(new Object[] { arg });
+            // add object to heap
+            youngHeap.add(obj);
+            log.append("New: ").append(obj).append("\n");
+        } catch (Exception ex) {
+            log.append("error creating object ").append(cls).append("\n");
+        }
+        return obj;
+    }
+
+    private static String getPackage() {
+        Package pack = Storage.class.getPackage();
+        if (pack != null && !pack.getName().equals("")) {
+            return pack.getName() + ".";
+        } else {
+            return "";
+        }
+    }
+
+    /* remove object from heap */
+    public static void delete(Collectable obj) {
+        if (youngHeap.remove(obj)) {
+            if (generationalGCActive) {
+                log.append("Delete young heap: ").append(obj).append("\n");
+            } else {
+                log.append("Delete heap: ").append(obj).append("\n");
+            }
+        } else if (oldHeap.remove(obj)) {
+            log.append("Delete old heap: ").append(obj).append("\n");
+        } else {
+            log.append("error trying to delete not existing object ").append(obj).append("\n");
+        }
+    }
+
+    /* get all root objects */
+    public static Iterable<Collectable> getRoot() {
+        return new LinkedList<>(root);
+    }
+
+    /* get young heap */
+    public static Iterable<Collectable> getYoungHeap() {
+        return new LinkedList<>(youngHeap);
+    }
+
+    /* get old heap */
+    public static Iterable<Collectable> getOldHeap() {
+        return new LinkedList<>(oldHeap);
+    }
+
+    /* get heap */
+    public static Iterable<Collectable> getHeap() {
+        return new LinkedList<>(youngHeap);
+    }
+
+    /* get references to collectables of an object */
+    public static Iterable<Collectable> getRefs(Collectable obj) {
+        // get all fields of an object
+        List<Collectable> fieldList = new LinkedList<>();
+        for (Field field : obj.getClass().getFields()) {
+            try {
+                Object o = field.get(obj);
+                if (o instanceof Collectable) {
+                    fieldList.add((Collectable) o);
+                }
+            } catch (Exception ex) {
+                ex.printStackTrace();
+            }
+        }
+        return fieldList;
+    }
+
+    /* dump an iterator */
+    public static void dump(String s, Iterable<Collectable> itr) {
+        log.append(s);
+        for (Collectable o : itr) {
+            log.append(" ").append(o);
+        }
+        log.append("\n");
+    }
+
+    public static String getLog() {
+        return log.toString();
+    }
+
+    private static void mark(Collectable cObject) {
+        // TODO Aufgabe 13.1
+        if (!cObject.isMarked()) {
+            cObject.setMark(true);
+
+            for (Collectable item : getRefs(cObject)) {
+                mark(item);
+            }
+        }
+    }
+
+    private static void sweep() {
+        // TODO Aufgabe 13.1 und Aufgabe 13.2
+        Map<Iterable<Collectable>, Consumer<Collectable>> heaps = new HashMap<>();
+        Consumer<Collectable> noOp = (item) -> {};
+
+        Consumer<Collectable> copy = (item) -> {
+            youngHeap.remove(item);
+            oldHeap.add(item);
+        };
+
+        heaps.put(getYoungHeap(), generationalGCActive ? copy : noOp);
+
+        if (!youngGenerationOnly) {
+            heaps.put(getOldHeap(), noOp);
+        }
+
+        for (Map.Entry<Iterable<Collectable>, Consumer<Collectable>> entry : heaps.entrySet()) {
+            for (Collectable item : entry.getKey()) {
+                if (!item.isMarked()) {
+                    delete(item);
+                } else {
+                    item.setMark(false);
+                    entry.getValue().accept(item);
+                }
+            }
+        }
+    }
+
+    public static void gc() {
+        if (generationalGCActive) {
+            if (youngGenerationOnly) {
+                log.append("\nCollector start young generation only\n");
+            } else {
+                log.append("\nCollector start young and old generation\n");
+            }
+        } else {
+            log.append("\nCollector start\n");
+        }
+
+        // TODO Aufgabe 13.1 und Aufgabe 13.2
+        for (Collectable item : getRoot()) {
+            mark(item);
+        }
+
+        sweep();
+
+        if (generationalGCActive) {
+            youngGenerationOnly = !youngGenerationOnly;
+        }
+
+        log.append("Collector end\n");
+    }
+}
diff --git a/app/src/main/java/ch/nuth/zhaw/exbox/TestCObjectServer.java b/app/src/main/java/ch/nuth/zhaw/exbox/TestCObjectServer.java
new file mode 100644
index 0000000..d601b11
--- /dev/null
+++ b/app/src/main/java/ch/nuth/zhaw/exbox/TestCObjectServer.java
@@ -0,0 +1,66 @@
+package ch.nuth.zhaw.exbox;
+
+public class TestCObjectServer implements CommandExecutor  {
+   private static CObject new_CObject(Object s) {
+      return (CObject) Storage._new("CObject", s);
+   }
+
+   static CObject a;
+   static CObject e;
+
+   public String execute (String input) {
+     run();
+     return Storage.getLog();
+   }
+
+  private void run() {
+     a = new_CObject("A");
+     CObject b = new_CObject("B");
+     CObject c = new_CObject("C");
+     CObject d = new_CObject("D");
+     e = new_CObject("E");
+     CObject f = new_CObject("F");
+     CObject g = new_CObject("G");
+     Storage.addRoot(a);
+     Storage.addRoot(e);
+     a.next = b; b.next = c; b.down = a; c.down = d;
+     e.next = f; f.next = g; g.next = e;
+     Storage.dump("\nRoots:", Storage.getRoot());
+     if (Storage.generationalGCActive) {
+        Storage.dump("\nYoung heap 1:", Storage.getYoungHeap());
+        Storage.dump("Old heap 1:", Storage.getOldHeap());
+     } else {
+        Storage.dump("Heap 1:", Storage.getYoungHeap());
+     }
+     Storage.gc();
+     if (Storage.generationalGCActive) {
+        Storage.dump("Young heap 2:", Storage.getYoungHeap());
+        Storage.dump("Old heap 2:", Storage.getOldHeap());
+     } else {
+        Storage.dump("Heap 2:", Storage.getYoungHeap());
+     }
+     b.next = f;
+     Storage.gc();
+     if (Storage.generationalGCActive) {
+        Storage.dump("Young heap 3:", Storage.getYoungHeap());
+        Storage.dump("Old heap 3:", Storage.getOldHeap());
+     } else {
+        Storage.dump("Heap 3:", Storage.getYoungHeap());
+     }
+     f.next = null;
+     Storage.gc();
+     if (Storage.generationalGCActive) {
+        Storage.dump("Young heap 4:", Storage.getYoungHeap());
+        Storage.dump("Old heap 4:", Storage.getOldHeap());
+     } else {
+        Storage.dump("Heap 4:", Storage.getYoungHeap());
+     }
+     Storage.gc();
+     if (Storage.generationalGCActive) {
+        Storage.dump("Young heap 5:", Storage.getYoungHeap());
+        Storage.dump("Old heap 5:", Storage.getOldHeap());
+     } else {
+        Storage.dump("Heap 5:", Storage.getYoungHeap());
+     }
+  }
+}
diff --git a/app/src/test/java/ch/nuth/zhaw/exbox/ADS13_1_test.java b/app/src/test/java/ch/nuth/zhaw/exbox/ADS13_1_test.java
new file mode 100644
index 0000000..9745fd5
--- /dev/null
+++ b/app/src/test/java/ch/nuth/zhaw/exbox/ADS13_1_test.java
@@ -0,0 +1,92 @@
+package ch.nuth.zhaw.exbox;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ADS13_1_test {
+    private CObject new_CObject(Object s) {
+        return (CObject) Storage._new("CObject", s);
+    }
+
+    static CObject a, d;
+    CObject b, c, e, f, g;
+
+    @BeforeEach
+    public void setUp() {
+        Storage.generationalGCActive = false;
+        Storage.clear();
+        newObjects();
+    }
+
+    private void testContent(String message, Iterable<Collectable> content, String expected) {
+        StringBuilder b = new StringBuilder();
+        content.forEach(b::append);
+        assertEquals(expected, b.toString(), message);
+    }
+
+    private void newObjects() {
+        a = new_CObject("A");
+        b = new_CObject("B");
+        c = new_CObject("C");
+        d = new_CObject("D");
+        e = new_CObject("E");
+        f = new_CObject("F");
+        g = new_CObject("G");
+        Storage.addRoot(a);
+        Storage.addRoot(d);
+        a.next = b;
+        b.next = c;
+        b.down = a;
+        c.down = d;
+        d.next = e;
+        e.next = f;
+        f.next = g;
+    }
+
+    @Test
+    public void testRoot() {
+        testContent("ROOT", Storage.getRoot(), "AD");
+    }
+
+    @Test
+    public void testInitialHeap() {
+        testContent("HEAP1", Storage.getHeap(), "ABCDEFG");
+    }
+
+    @Test
+    public void testAfterFirstGC() {
+        Storage.gc();
+        testContent("HEAP2", Storage.getHeap(), "ABCDEFG");
+    }
+
+    @Test
+    public void testAfterFirstChangeGC() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        testContent("HEAP3", Storage.getHeap(), "ABCDE");
+    }
+
+    @Test
+    public void testAfterSecondChangeGC() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        a.next = null;
+        Storage.gc();
+        testContent("HEAP4", Storage.getHeap(), "ADE");
+    }
+
+    @Test
+    public void testFinalHeap() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        a.next = null;
+        Storage.gc();
+        Storage.gc();
+        testContent("HEAP5", Storage.getHeap(), "ADE");
+    }
+}
diff --git a/app/src/test/java/ch/nuth/zhaw/exbox/ADS13_3_test.java b/app/src/test/java/ch/nuth/zhaw/exbox/ADS13_3_test.java
new file mode 100644
index 0000000..f86cf10
--- /dev/null
+++ b/app/src/test/java/ch/nuth/zhaw/exbox/ADS13_3_test.java
@@ -0,0 +1,130 @@
+package ch.nuth.zhaw.exbox;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ADS13_3_test {
+    private CObject new_CObject(Object s) {
+        return (CObject) Storage._new("CObject", s);
+    }
+
+    static CObject a, d;
+    CObject b, c, e, f, g, h;
+
+    @BeforeEach
+    public void setUp() {
+        Storage.generationalGCActive = true;
+        Storage.youngGenerationOnly = true;
+        Storage.clear();
+        newObjects();
+    }
+
+    private void testContent(String message, Iterable<Collectable> content, String expected) {
+        StringBuilder b = new StringBuilder();
+        content.forEach(b::append);
+        assertEquals(expected, b.toString(), message);
+    }
+
+    private void newObjects() {
+        a = new_CObject("A");
+        b = new_CObject("B");
+        c = new_CObject("C");
+        d = new_CObject("D");
+        e = new_CObject("E");
+        f = new_CObject("F");
+        g = new_CObject("G");
+        Storage.addRoot(a);
+        Storage.addRoot(d);
+        a.next = b;
+        b.next = c;
+        b.down = a;
+        c.down = d;
+        d.next = e;
+        e.next = f;
+        f.next = g;
+    }
+
+    @Test
+    public void testRoot() {
+        testContent("ROOT", Storage.getRoot(), "AD");
+    }
+
+    @Test
+    public void testInitialHeap() {
+        testContent("YOUNG HEAP1", Storage.getYoungHeap(), "ABCDEFG");
+        testContent("OLD HEAP1", Storage.getOldHeap(), "");    }
+
+    @Test
+    public void testAfterFirstGC() {
+        Storage.gc();
+        Storage.getYoungHeap();
+        Storage.getOldHeap();
+        testContent("YOUNG HEAP2", Storage.getYoungHeap(), "");
+        testContent("OLD HEAP2", Storage.getOldHeap(), "ABCDEFG");
+    }
+
+    @Test
+    public void testAfterFirstChangeGC() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        testContent("YOUNG HEAP3", Storage.getYoungHeap(), "");
+        testContent("OLD HEAP3", Storage.getOldHeap(), "ABCDE");
+    }
+
+    @Test
+    public void testAfterSecondChangeGC() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        a.next = null;
+        Storage.gc();
+        testContent("YOUNG HEAP4", Storage.getYoungHeap(), "");
+        testContent("OLD HEAP4", Storage.getOldHeap(), "ABCDE");
+    }
+
+    @Test
+    public void testAfterSecondCallGC() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        a.next = null;
+        Storage.gc();
+        Storage.gc();
+        testContent("YOUNG HEAP5", Storage.getYoungHeap(), "");
+        testContent("OLD HEAP5", Storage.getOldHeap(), "ADE");
+    }
+
+    @Test
+    public void testAfterAddObjecthGC() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        a.next = null;
+        Storage.gc();
+        Storage.gc();
+        h = new_CObject("H");
+        a.next = h;
+        testContent("YOUNG HEAP5", Storage.getYoungHeap(), "H");
+        testContent("OLD HEAP5", Storage.getOldHeap(), "ADE");
+    }
+
+    @Test
+    public void testFinalHeap() {
+        Storage.gc();
+        e.next = d;
+        Storage.gc();
+        a.next = null;
+        Storage.gc();
+        Storage.gc();
+        h = new_CObject("H");
+        a.next = h;
+        testContent("YOUNG HEAP5", Storage.getYoungHeap(), "H");
+        testContent("OLD HEAP5", Storage.getOldHeap(), "ADE");
+        Storage.gc();
+        testContent("YOUNG HEAP5", Storage.getYoungHeap(), "");
+        testContent("OLD HEAP5", Storage.getOldHeap(), "ADEH");
+    }
+}