diff --git a/pom.xml b/pom.xml
index a1613eb..1dfc8fa 100644
--- a/pom.xml
+++ b/pom.xml
@@ -59,8 +59,8 @@
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.3</version>
                 <configuration>
-                    <source>1.7</source>
-                    <target>1.7</target>
+                    <source>1.8</source>
+                    <target>1.8</target>
                 </configuration>
             </plugin>
             <plugin>
diff --git a/src/main/java/ru/spbau/mit/Injector.java b/src/main/java/ru/spbau/mit/Injector.java
index c54168d..dcd296a 100644
--- a/src/main/java/ru/spbau/mit/Injector.java
+++ b/src/main/java/ru/spbau/mit/Injector.java
@@ -1,9 +1,16 @@
 package ru.spbau.mit;
 
-import java.util.List;
+import java.lang.reflect.Constructor;
+import java.lang.reflect.InvocationTargetException;
+import java.util.*;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
 
 
 public final class Injector {
+    private static Map<String, Object> alreadyCreatedObjects = new HashMap<>();
+    private static Set<String> enqueued = new HashSet<>();
+
     private Injector() {
     }
 
@@ -12,6 +19,71 @@ private Injector() {
      * `implementationClassNames` for concrete dependencies.
      */
     public static Object initialize(String rootClassName, List<String> implementationClassNames) throws Exception {
-        throw new IllegalStateException();
+        try {
+            return initialize0(rootClassName, implementationClassNames);
+        } finally {
+            deinitializeStructures();
+        }
+    }
+
+    private static void deinitializeStructures() {
+        alreadyCreatedObjects.clear();
+        enqueued.clear();
+    }
+
+    private static Object initialize0(String rootClassName, List<String> implementationClassNames)
+            throws ImplementationNotFoundException,
+            ClassNotFoundException,
+            AmbiguousImplementationException,
+            InjectionCycleException {
+        if (alreadyCreatedObjects.containsKey(rootClassName)) {
+            return alreadyCreatedObjects.get(rootClassName);
+        }
+        if (enqueued.contains(rootClassName)) {
+            return new InjectionCycleException();
+        }
+        enqueued.add(rootClassName);
+
+        Class rootClass = Class.forName(rootClassName);
+        Constructor rootConstructor = rootClass.getConstructors()[0];
+        List<Object> args = new ArrayList<>();
+        for (Class<?> dependencyClass : rootConstructor.getParameterTypes()) {
+            Predicate<String> predicate = (implName) -> {
+                try {
+                    Class implementationClass = Class.forName(implName);
+                    return dependencyClass.isAssignableFrom(implementationClass);
+                } catch (ClassNotFoundException e) {
+                    throw new RuntimeException();
+                }
+            };
+            List<String> allowedClasses = implementationClassNames
+                    .stream()
+                    .filter(predicate)
+                    .collect(Collectors.toList());
+
+            if (allowedClasses.size() == 1) {
+                String allowedClass = allowedClasses.get(0);
+                Object arg = initialize0(allowedClass, implementationClassNames);
+                args.add(arg);
+            } else if (allowedClasses.size() > 1) {
+                throw new AmbiguousImplementationException();
+            } else {
+                if (enqueued.stream().anyMatch(predicate)) {
+                    throw new InjectionCycleException();
+                } else {
+                    throw new ImplementationNotFoundException();
+                }
+            }
+        }
+
+        Object rootObject;
+        try {
+            rootObject = rootConstructor.newInstance(args.toArray());
+        } catch (InstantiationException | IllegalAccessException | InvocationTargetException e) {
+            throw new RuntimeException();
+        }
+        enqueued.remove(rootClassName);
+        alreadyCreatedObjects.put(rootClassName, rootObject);
+        return rootObject;
     }
 }