import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;

public class StartReceiver extends BroadcastReceiver {

        @Override
        public void onReceive(Context context, Intent intent) {
                String action = intent.getAction();

                if(action.equals("android.intent.action.BOOT_COMPLETED")) {
                        Intent i = new Intent(context, MainActivity.class);
                        i.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
                        context.startActivity(i);
                }
        }

}

    <uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />

    <application .....>

        <receiver android:name=".StartReceiver"
            android:enabled="true"
            android:exported="false"
            android:label="StartReceiver"
            >
            <intent-filter>
                <action android:name="android.intent.action.BOOT_COMPLETED" />
            </intent-filter>
        </receiver>

    </application>