Facebook Login example Android

 MainActivity.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:gravity="center"
    android:layout_height="match_parent"
    tools:context=".LoginActivity2">


    <com.facebook.login.widget.LoginButton
        android:id="@+id/login_button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="30dp"
        android:layout_marginBottom="30dp" />

</LinearLayout>

MainActivity.java

public class LoginActivity2 extends AppCompatActivity {

    private CallbackManager callbackManager;
    private LoginButton loginButton;
    private static final String EMAIL = "email";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_login2);

        callbackManager = CallbackManager.Factory.create();
        loginButton = (LoginButton) findViewById(R.id.login_button);
        loginButton.setReadPermissions(Arrays.asList(EMAIL));

        // Callback registration
        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {
                // App code
                FBLogin(loginResult.getAccessToken());
            }

            @Override
            public void onCancel() {
                // App code
            }

            @Override
            public void onError(FacebookException exception) {
                // App code
            }
        });

    }

    void FBLogin(AccessToken accessToken)
    {
        AuthCredential authCredential = FacebookAuthProvider.getCredential(accessToken.getToken());
        FirebaseAuth firebaseAuth=FirebaseAuth.getInstance();
        firebaseAuth.signInWithCredential(authCredential).addOnSuccessListener(new OnSuccessListener<AuthResult>() {
            @Override
            public void onSuccess(AuthResult authResult) {
                Toast.makeText(LoginActivity2.this, "Success", Toast.LENGTH_SHORT).show();
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(LoginActivity2.this, "Failed "+e.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });


    }
}