Revert "Remove usage of Java 8 features (lambdas)"

This reverts commit 24813d0.

Author: tom-andersen

src/main/java/com/google/firebase/cloud/FirestoreClient.java

@@ -14,7 +14,6 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
-import java.util.function.Function;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -140,24 +139,16 @@ private static class FirestoreInstances {
     private final FirebaseApp app;
 
     private final Map<String, FirestoreClient> clients =
-        Collections.synchronizedMap(new HashMap<String, FirestoreClient>());
+        Collections.synchronizedMap(new HashMap<>());
 
     private FirestoreInstances(FirebaseApp app) {
       this.app = app;
     }
 
     FirestoreClient get(String databaseId) {
-      return clients.computeIfAbsent(databaseId, newFirestoreInstance);
+      return clients.computeIfAbsent(databaseId, id -> new FirestoreClient(app, id));
     }
 
-    private final Function<String, FirestoreClient> newFirestoreInstance =
-        new Function<String, FirestoreClient>() {
-          @Override
-          public FirestoreClient apply(String id) {
-            return new FirestoreClient(app, id);
-          }
-        };
-
     void destroy() {
       synchronized (clients) {
         for (FirestoreClient client : clients.values()) {

src/test/java/com/google/firebase/cloud/FirestoreClientTest.java

@@ -19,7 +19,6 @@
 import java.io.IOException;
 import org.junit.After;
 import org.junit.Test;
-import org.junit.function.ThrowingRunnable;
 
 public class FirestoreClientTest {
 
@@ -136,7 +135,7 @@ public void testFirestoreOptionsOverride() throws IOException {
   @Test
   public void testAppDelete() throws IOException {
     final String databaseId = "databaseIdInTestAppDelete";
-    final FirebaseApp app = FirebaseApp.initializeApp(FirebaseOptions.builder()
+    FirebaseApp app = FirebaseApp.initializeApp(FirebaseOptions.builder()
         .setCredentials(GoogleCredentials.fromStream(ServiceAccount.EDITOR.asStream()))
         .setProjectId("mock-project-id")
         .setFirestoreOptions(FIRESTORE_OPTIONS)
@@ -152,33 +151,13 @@ public void testAppDelete() throws IOException {
 
     assertNotSame(firestore1, firestore2);
 
-    final DocumentReference document = firestore1.collection("collection").document("doc");
+    DocumentReference document = firestore1.collection("collection").document("doc");
     app.delete();
 
-    assertThrows(IllegalStateException.class, new ThrowingRunnable() {
-      public void run() {
-        FirestoreClient.getFirestore(app);
-      }
-    });
-    assertThrows(IllegalStateException.class, new ThrowingRunnable() {
-      public void run() throws Throwable {
-        document.get();
-      }
-    });
-    assertThrows(IllegalStateException.class, new ThrowingRunnable() {
-      public void run() throws Throwable {
-        FirestoreClient.getFirestore();
-      }
-    });
-    assertThrows(IllegalStateException.class, new ThrowingRunnable() {
-      public void run() throws Throwable {
-        FirestoreClient.getFirestore(app, databaseId);
-      }
-    });
-    assertThrows(IllegalStateException.class, new ThrowingRunnable() {
-      public void run() throws Throwable {
-        FirestoreClient.getFirestore(databaseId);
-      }
-    });
+    assertThrows(IllegalStateException.class, () -> FirestoreClient.getFirestore(app));
+    assertThrows(IllegalStateException.class, () -> document.get());
+    assertThrows(IllegalStateException.class, () -> FirestoreClient.getFirestore());
+    assertThrows(IllegalStateException.class, () -> FirestoreClient.getFirestore(app, databaseId));
+    assertThrows(IllegalStateException.class, () -> FirestoreClient.getFirestore(databaseId));
   }
 }