package com.starter.android_starter;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Intent intent = new Intent(this,Login.class);
        startActivity(intent);
    }
}

package com.starter.android_starter;

import android.content.Intent;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {
private static final String TWITTER_KEY = "your twitter key";
    private static final String TWITTER_SECRET = "your twitter secret";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
          TwitterAuthConfig authConfig = new TwitterAuthConfig(TWITTER_KEY, TWITTER_SECRET);
        Fabric.with(this, new Twitter(authConfig));
        setContentView(R.layout.activity_main);
        Intent intent = new Intent(this,Login.class);
        startActivity(intent);
    }
}

Update MainActivity.java