Remove usage of Java 8 features (lambdas)

Author: tom-andersen

Diff for: src/main/java/com/google/firebase/cloud/FirestoreClient.java

@@ -14,6 +14,7 @@
 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;
 
@@ -139,16 +140,24 @@ private static class FirestoreInstances {
     private final FirebaseApp app;
 
     private final Map<String, FirestoreClient> clients =
-        Collections.synchronizedMap(new HashMap<>());
+        Collections.synchronizedMap(new HashMap<String, FirestoreClient>());
 
     private FirestoreInstances(FirebaseApp app) {
       this.app = app;
     }
 
     FirestoreClient get(String databaseId) {
-      return clients.computeIfAbsent(databaseId, id -> new FirestoreClient(app, id));
+      return clients.computeIfAbsent(databaseId, newFirestoreInstance);
     }
 
+    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()) {

Diff for: src/test/java/com/google/firebase/cloud/FirestoreClientTest.java

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