LoginActivity.java

package br.com.geifferson.today;

import android.content.Intent;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.content.pm.Signature;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.util.Base64;
import android.util.Log;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.GraphRequest;
import com.facebook.GraphResponse;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;
import com.squareup.picasso.Picasso;

import org.json.JSONException;
import org.json.JSONObject;
import org.w3c.dom.Text;

import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.Arrays;


public class LoginActivity extends AppCompatActivity {

    private LoginButton loginButton;
    private CallbackManager callbackManager;
    private ImageView  fotoFacebook;
    private TextView nomeFacebook;
    private TextView emailFacebook;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_login);
        fotoFacebook = (ImageView) findViewById(R.id.fotofacebook);
        nomeFacebook = (TextView) findViewById(R.id.NomeDaPessoa);
        emailFacebook = (TextView) findViewById(R.id.emailDaPessoa);

        callbackManager = CallbackManager.Factory.create();

        loginButton = (LoginButton) findViewById(R.id.loginButton);

        loginButton.setReadPermissions(Arrays.asList("email"));

        loginButton.registerCallback(callbackManager, new FacebookCallback<LoginResult>() {
            @Override
            public void onSuccess(LoginResult loginResult) {

                GraphRequest graphRequest   =   GraphRequest.newMeRequest(loginResult.getAccessToken(), new GraphRequest.GraphJSONObjectCallback()
                {
                    @Override
                    public void onCompleted(JSONObject object, GraphResponse response)
                    {
                        Toast.makeText(LoginActivity.this, "Logado com Sucesso", Toast.LENGTH_SHORT).show();
                        Log.d(">>>>",object.toString());
                        try {
                            String NomeDaPessoa = object.getString("name");
                            String emailDaPessoa = object.getString("email");

                            JSONObject jsonFoto = object.getJSONObject("picture");
                            JSONObject jsonFotoData = jsonFoto.getJSONObject("data");
                            String photoUrl = jsonFotoData.getString("url");

                            goMainScreen(NomeDaPessoa, photoUrl, emailDaPessoa);

                        } catch (JSONException e) {
                            e.printStackTrace();
                        }

                    }
                });

                Bundle parameters = new Bundle();
                parameters.putString("fields", "id,name,first_name,last_name,email,picture");
                graphRequest.setParameters(parameters);
                graphRequest.executeAsync();


            }

            @Override
            public void onCancel() {
                Toast.makeText(getApplicationContext(), R.string.cancel_login, Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onError(FacebookException error) {
                Toast.makeText(getApplicationContext(), R.string.error_login, Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void goMainScreen(String nomeDaPessoa, String photoUrl, String emailDaPessoa) {
        Intent intent = new Intent(this, MainActivity.class);
        intent.putExtra("nome", nomeDaPessoa);
        intent.putExtra("photoUrl",photoUrl);
      intent.putExtra("emailDaPessoa",emailDaPessoa);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(intent);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        callbackManager.onActivityResult(requestCode, resultCode, data);
    }
}

main_activity.xml

<!-- Adiciona esse textview no teu layout e posiciona ele onde tu quer -->

<Textview
          android:id="@+id/emailDaPessoa"
          android:width="wrap_content"
          android:height="wrap_content" />

MainActivity.java

package br.com.geifferson.today;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

import com.facebook.AccessToken;
import com.facebook.login.LoginManager;
import com.squareup.picasso.Picasso;


public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
      
        TextView nome = (TextView) findViewById(R.id.NomeDaPessoa);
        ImageView imagem = (ImageView) findViewById(R.id.fotofacebook);
        TextView email = (TextView) findViewById(R.id.emailDaPessoa);
      
        if (getIntent().hasExtra("nome")){
            nome.setText(getIntent().getStringExtra("nome"));
            email.setText(getIntent().getStringExtra("emailDaPessoa"));
            Picasso.with(MainActivity.this).load(getIntent().getStringExtra("photoUrl"))
                    .into(imagem);
        }

        if (AccessToken.getCurrentAccessToken() == null) {
            goLoginScreen();
        }

    }

    private void goLoginScreen() {
        Intent intent = new Intent(this, LoginActivity.class);
        intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP | Intent.FLAG_ACTIVITY_CLEAR_TASK | Intent.FLAG_ACTIVITY_NEW_TASK);
        startActivity(intent);

    }
    public void link(View v) {
        startActivity(new Intent(this, LinkActivity.class));
    }


    public void logout(View view) {
        LoginManager.getInstance().logOut();
        Toast.makeText(MainActivity.this, "Encerrado com Sucesso", Toast.LENGTH_SHORT).show();
        goLoginScreen();
    }
}