docs: began merging variant client samples (#696)

Author: craiglabenz

samples/snippets/src/main/java/com/example/firestore/Quickstart.java

@@ -43,19 +43,10 @@ public class Quickstart {
 
  private Firestore db;
 
- /**
- * Initialize Firestore using default project ID.
- */
- public Quickstart() {
- // [START fs_initialize]
- // [START firestore_setup_client_create]
- Firestore db = FirestoreOptions.getDefaultInstance().getService();
- // [END firestore_setup_client_create]
- // [END fs_initialize]
- this.db = db;
- }
-
  public Quickstart(String projectId) throws Exception {
+ // [START firestore_setup_client_create]
+ // Option 1: Initialize a Firestore client with a specific `projectId` and
+ // authorization credential.
  // [START fs_initialize_project_id]
  // [START firestore_setup_client_create_with_project_id]
  FirestoreOptions firestoreOptions =
@@ -64,8 +55,24 @@ public Quickstart(String projectId) throws Exception {
  .setCredentials(GoogleCredentials.getApplicationDefault())
  .build();
  Firestore db = firestoreOptions.getService();
- // [END firestore_setup_client_create_with_project_id]
  // [END fs_initialize_project_id]
+ // [END firestore_setup_client_create_with_project_id]
+ // [END firestore_setup_client_create]
+ this.db = db;
+ }
+
+ /**
+ * Initialize Firestore using default project ID.
+ */
+ public Quickstart() {
+ // [START firestore_setup_client_create]
+
+ // Option 2: Initialize a Firestore client with default values inferred from
+ // your environment.
+ // [START fs_initialize]
+ Firestore db = FirestoreOptions.getDefaultInstance().getService();
+ // [END firestore_setup_client_create]
+ // [END fs_initialize]
  this.db = db;
  }