Question

Exception in thread "main" java.lang.NullPointerException at Client.main(Client.java:10)

求教为啥是这样的错误 怎么改
import java.io.*;import java.net.*;
public class Client {
public static void main(String [] args) throws Exception {
Socket socket = null;

BufferedReader keyBoard = new BufferedReader(new InputStreamReader(System.in));

DataOutputStream toserver = new DataOutputStream(socket.getOutputStream());

BufferedReader fromserver= new BufferedReader(new InputStreamReader(socket.getInputStream()));

String ip="127.0.0.1";
String data = keyBoard.readLine();
String serverData=fromserver.readLine();
int port=80;
try {
socket=new Socket(ip,port);
toserver.writeBytes(data+'\n');
System.out.println("服务器反馈："+serverData);

} catch (Exception e) {
// TODO: handle exception
}
socket.close();

Answer 1

Socket还没实例化就用了
socket.getInputStream()

肯定报空指针错误

需要在
public static void main(String [] args) throws Exception {
Socket socket = null;
下面实例化socket对象

Answer 2

意思是：第10行出现空指针错误，也就是创建的对象不存在。你可以在第10行检查，需要对创建对象的那一句进行检查。

Answer 3

空据指针异常了，把所有的值都用System.out.println()打出来看看哪一个不能为空但又是空的呗

Answer 4

没有获取到相应的参数吧，空指针异常。。。

Answer 5

import java.io.*;import java.net.*;
public class Client {
public static void main(String [] args) throws Exception {
Socket socket = null;
try {
String ip="127.0.0.1";
int port=80;
socket=new Socket(ip,port);
BufferedReader keyBoard = new BufferedReader(new InputStreamReader(System.in));
DataOutputStream toserver = new DataOutputStream(socket.getOutputStream());
BufferedReader fromserver= new BufferedReader(new InputStreamReader(socket.getInputStream()));
String data = keyBoard.readLine();
String serverData=fromserver.readLine();
toserver.writeBytes(data+'\n');
System.out.println("服务器反馈："+serverData);
socket.close();
} catch (Exception e) {

System.out.println(e.getMessage());
}

}
}

追问

e.getmessage()能得到啥

Answer 6

空指针异常

Answer 7

DataOutputStream toserver = new DataOutputStream(socket.getOutputStream());

你socket为空，这件调用它的getOutputStream()报空值异常。要先实例化。