Exiting the App when Using FireBase Database on Android Studio (Java)

Question

Need to use firebase database I:

• Create an account on FireBase and create simple json file which shows the Hierarchy of the Database and Add it to the Realtime DataBase.

• Add these dependencies to the build.gradle(Module) File:

  compile 'com.google.firebase:firebase-core:10.2.0'

  compile 'com.google.firebase:firebase-database:10.2.0'

• I made two activities the main activity has two buttons when you click at the Sign in Button the second activity starts.(It was working very well until I add the Firebase using these commands):(the App Crush (Exiting))

  FirebaseDatabase database = FirebaseDatabase.getInstance();

  DatabaseReference table_user = database.getReference("User");

Answer 1

I should add on Gradle (Project File):

dependencies {
    classpath 'com.google.gms:google-services:3.0.0'
}

And Add on Gradle on (Module File):

dependencies {
.
.
.
 }
apply plugin: 'com.google.gms.google-services'