MainActivity.java

package com.paperwrrk;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.support.multidex.MultiDex;
import android.view.View;
import android.widget.Button;

import com.google.android.youtube.player.YouTubeBaseActivity;
import com.google.android.youtube.player.YouTubeInitializationResult;
import com.google.android.youtube.player.YouTubePlayer;
import com.google.android.youtube.player.YouTubePlayerView;

public class MainActivity extends YouTubeBaseActivity implements View.OnClickListener {

    Button mbutton;
    Button btn2;
    private YouTubePlayerView myouTubePlayerView;
    private YouTubePlayer.OnInitializedListener monInitializedListener;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        myouTubePlayerView = (YouTubePlayerView) findViewById(R.id.youtube_player_view);
        monInitializedListener = new YouTubePlayer.OnInitializedListener() {
            @Override
            public void onInitializationSuccess(YouTubePlayer.Provider provider, YouTubePlayer youTubePlayer, boolean b) {
                youTubePlayer.loadVideo("_GuOjXYl5ew");
            }

            @Override
            public void onInitializationFailure(YouTubePlayer.Provider provider, YouTubeInitializationResult youTubeInitializationResult) {

            }
        };

        mbutton = (Button) findViewById(R.id.button_play_youtube_video);
        btn2 =(Button) findViewById(R.id.btn2);
        mbutton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
              myouTubePlayerView.initialize("Your API-KEY", monInitializedListener);// you can also have a separate class for API KEY
            }
        });
    }
    @Override
    public void onClick(View view){
        if (view == btn2){
            startActivity(new Intent(this, Activity2.class));
        }
    }
    @Override
    protected void attachBaseContext(Context newBase) {

        super.attachBaseContext(newBase);

        MultiDex.install(this);
    }

}