Fix sample app style issues

Summary:
Start adding Nullable and finals in some places to
make our sample app (and hopefully rest of the codebase) follow
some of the standards we have in place elsewhere.

Reviewed By: jknoxville

Differential Revision: D10463816

fbshipit-source-id: 7df6758919331ba8a334c94214b9e02bbab8cd2d

android/sample/src/main/java/com/facebook/flipper/sample/FlipperSampleApplication.java

@@ -9,6 +9,7 @@ package com.facebook.flipper.sample;
 
 import android.app.Application;
 import android.content.Context;
+import android.support.annotation.Nullable;
 import com.facebook.flipper.android.AndroidFlipperClient;
 import com.facebook.flipper.core.FlipperClient;
 import com.facebook.flipper.plugins.example.ExampleFlipperPlugin;
@@ -28,7 +29,7 @@ import okhttp3.OkHttpClient;
 
 public class FlipperSampleApplication extends Application {
 
-  public static OkHttpClient okhttpClient;
+  @Nullable public static OkHttpClient sOkHttpClient = null;
 
   @Override
   public void onCreate() {
@@ -38,10 +39,10 @@ public class FlipperSampleApplication extends Application {
     final FlipperClient client = AndroidFlipperClient.getInstance(this);
     final DescriptorMapping descriptorMapping = DescriptorMapping.withDefaults();
 
-    NetworkFlipperPlugin networkPlugin = new NetworkFlipperPlugin();
+    final NetworkFlipperPlugin networkPlugin = new NetworkFlipperPlugin();
-    FlipperOkhttpInterceptor interceptor = new FlipperOkhttpInterceptor(networkPlugin);
+    final FlipperOkhttpInterceptor interceptor = new FlipperOkhttpInterceptor(networkPlugin);
 
-    okhttpClient =
+    sOkHttpClient =
         new OkHttpClient.Builder()
             .addNetworkInterceptor(interceptor)
             .connectTimeout(60, TimeUnit.SECONDS)

android/sample/src/main/java/com/facebook/flipper/sample/MainActivity.java

@@ -19,14 +19,14 @@ import com.facebook.litho.LithoView;
 public class MainActivity extends AppCompatActivity {
 
   @Override
-  protected void onCreate(Bundle savedInstanceState) {
+  protected void onCreate(final Bundle savedInstanceState) {
     super.onCreate(savedInstanceState);
     final ComponentContext c = new ComponentContext(this);
     setContentView(LithoView.create(c, RootComponent.create(c).build()));
 
-    FlipperClient client = AndroidFlipperClient.getInstanceIfInitialized();
+    final FlipperClient client = AndroidFlipperClient.getInstanceIfInitialized();
     if (client != null) {
-      FlipperPlugin samplePlugin = client.getPlugin(ExampleFlipperPlugin.ID);
+      final FlipperPlugin samplePlugin = client.getPlugin(ExampleFlipperPlugin.ID);
       if (samplePlugin instanceof ExampleFlipperPlugin) {
         ((ExampleFlipperPlugin) samplePlugin).setActivity(this);
       }

android/sample/src/main/java/com/facebook/flipper/sample/RootComponentSpec.java

@@ -68,7 +68,7 @@ public class RootComponentSpec {
 
     final Request request =
         new Request.Builder().url("https://api.github.com/repos/facebook/yoga").get().build();
-    FlipperSampleApplication.okhttpClient
+    FlipperSampleApplication.sOkHttpClient
         .newCall(request)
         .enqueue(
             new Callback() {
@@ -101,7 +101,7 @@ public class RootComponentSpec {
             .post(formBody)
             .build();
 
-    FlipperSampleApplication.okhttpClient
+    FlipperSampleApplication.sOkHttpClient
         .newCall(request)
         .enqueue(
             new Callback() {