新人求助

[liuhuannnnn]

刚刚学习安卓scoket通信，在网上找了个代码运行出现：
FATAL EXCEPTION: main
Process: com.liuhuan, PID: 3760
java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.net.Socket.isConnected()' on a null object reference
at com.liuhuan.MainActivity$2.onClick(MainActivity.java:66)
at android.view.View.performClick(View.java:5198)
at android.view.View$PerformClick.run(View.java:21147)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
请问可能是什么原因？