添加访问权限（AndroidManifest.xml文件里）

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

Java代码（MainActivity.java文件）

    package com.example.androidtest;  
      
    import android.net.ConnectivityManager;  
    import android.net.NetworkInfo.State;  
    import android.os.Bundle;  
    import android.app.Activity;  
    import android.content.Context;  
    import android.util.Log;  
    import android.view.Menu;  
      
    public class MainActivity extends Activity {  
      
        @Override  
        protected void onCreate(Bundle savedInstanceState) {  
            super.onCreate(savedInstanceState);  
            setContentView(R.layout.activity_main);  
              
            boolean bFlag = isWifiAvailable(this.getApplicationContext());  
            if (bFlag) {  
                Log.i("Wifi state - ", "connected");  
            } else {  
                Log.i("Wifi state - ", "not connected");  
            }  
              
        }  
          
        /** 
         * 判断wifi连接状态 
         *  
         * @param ctx 
         * @return 
         */  
        public boolean isWifiAvailable(Context ctx) {  
            ConnectivityManager conMan = (ConnectivityManager) ctx  
                    .getSystemService(Context.CONNECTIVITY_SERVICE);  
            State wifi = conMan.getNetworkInfo(ConnectivityManager.TYPE_WIFI)  
                    .getState();  
            if (State.CONNECTED == wifi) {  
                return true;  
            } else {  
                return false;  
            }  
        }  
          
        @Override  
        public boolean onCreateOptionsMenu(Menu menu) {  
            // Inflate the menu; this adds items to the action bar if it is present.  
            getMenuInflater().inflate(R.menu.activity_main, menu);  
            return true;  
        }  
      
    }