java 安卓填充另一个类ArrayList

Question

我试图编写一个代码，从异步任务的输出中的一个类填充一个数组

现在代码给了我空引用。。把代码放在下面

数组类：

public class ClientDiscovery {
public static ArrayList<InetAddress> clientes;

public static void addclient(InetAddress address)
{
clientes.add(address);
}

public static void removeclient(InetAddress address)   
{
clientes.remove(address);
}

public static ArrayList<InetAddress>getclient()
{
Set<InetAddress> noduplicate = new HashSet<>();
if (!(clientes ==null)) {
    noduplicate.addAll(clientes);
    clientes.clear();
    clientes.addAll(noduplicate);
}
return clientes;
}

}

异步任务填充数组

public class RequestDiscoveryAsyncTask extends AsyncTask<Void,Void,Void>{

Context context;
public RequestDiscoveryAsyncTask(Context context) {
    this.context = context.getApplicationContext();
}

@Override
protected Void doInBackground(Void...voids) {


     ///HERE I INITIALIZE THE SOCKETS ****INTENTIONALLY OMITED TO EASY READING*** 


    /*HERE I INTENT TO GET THE ACK BACK FROM THE CLIENTES "MY CUSTOM ACK"*/

    while(!timeout) {
        byte[] ready = new byte[5];

        DatagramPacket pkgready = new DatagramPacket(ready, 0, 5);
            socket.receive(pkgready);
        if (new String(pkgready.getData()).contains("READY"))
            ClientDiscovery.addclient(pkgready.getAddress());
        }

    }
return null;
}


}

为了便于阅读，省略了socket初始化和捕获异常

日志：

07-18 21:50:43.889    4327-5025/fr.xplod.focal E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
java.lang.RuntimeException: An error occured while executing doInBackground()
        at 安卓.os.AsyncTask$3.done(AsyncTask.java:299)
        at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:352)
        at java.util.concurrent.FutureTask.setException(FutureTask.java:219)
        at java.util.concurrent.FutureTask.run(FutureTask.java:239)
        at 安卓.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
        at java.lang.Thread.run(Thread.java:838)
 Caused by: java.lang.NullPointerException
        at org.cyanogenmod.focal.ClientDiscovery.addclient(ClientDiscovery.java:16)
        at org.cyanogenmod.focal.RequestDiscoveryAsyncTask.doInBackground(RequestDiscoveryAsyncTask.java:68)
        at org.cyanogenmod.focal.RequestDiscoveryAsyncTask.doInBackground(RequestDiscoveryAsyncTask.java:23)
        at 安卓.os.AsyncTask$2.call(AsyncTask.java:287)
        at java.util.concurrent.FutureTask.run(FutureTask.java:234)
  at 安卓.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
        atjava.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
        atjava.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
        at java.lang.Thread.run(Thread.java:838)

Answer 1

仅创建对象，当前ArrayList对象不存在 添加此行： public static ArrayList<InetAddress> clientes = new ArrayList<InetAddress>();