最近在自学第一行代码遇到问题实在想不出怎么解决求大神

package com.example.windows10.broadcast;

import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.ConnectivityManager;
import android.net.NetworkInfo;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {
    private IntentFilter intentFilter;
    private NetworkChangeReceiver networkChangeReceiver;

    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        intentFilter = new IntentFilter();
        intentFilter.addAction("android.net.conn.CONNECTIVITY_CHANGE");//系统网络发生变化的时候会发出一条android.net.conn.CONNECTIVITY_CHANGE的指令
        networkChangeReceiver = new NetworkChangeReceiver();//创建一个实例
        registerReceiver(networkChangeReceiver, intentFilter);//调用registerReceiver方法进行注册并且把intentFilter也放入让networkChangeRecelver可以实现接收
    }

    protected void onDestroy() {//注销广播
        super.onDestroy();
        unregisterReceiver(networkChangeReceiver);//调用unregisterReceive取消注册networkChangeRecelver
    }

    class NetworkChangeReceiver extends BroadcastReceiver {
        @Override
        public void onReceive(Context context, Intent intent) {
            ConnectivityManager connectionManager = (ConnectivityManager) getSystemService(MainActivity.CONNECTIVITY_SERVICE);
            NetworkInfo networkInfo = connectionManager.getActiveNetworkInfo();
            if (networkInfo != null && networkInfo.isAvailable()) {
                Toast.makeText(MainActivity.this, "网络可用", Toast.LENGTH_SHORT);
            } else {
                Toast.makeText(MainActivity.this, "网络不可用", Toast.LENGTH_SHORT).show();
            }
        }
    }

}

描述：一到模拟器运行仿真的时候会直接stop不知道问题出哪里了 文件权限也按照书里写了

这个是报错的logcat：