代码如下：
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import *;
import *;
import java.util.*;

class A {
    public ServerSocket server = null;
    public Socket client = null;
    public static boolean flag = true;    //此处我设置成静态
    public Scanner sc = null;

    public A() throws Exception {
        server = new ServerSocket(8888);
        System.out.println("已建立服务端");

        while (A.flag) {    //如果A.flag为false则，服务端终止
            client = server.accept();
            System.out.println("一客户端连入");

            sc = new Scanner(client.getInputStream());

            while (sc.hasNext()) {
                String str = sc.nextLine();
                System.out.println(str);
            }

            sc.close();
        }
    }
}

class B {
    public Socket client = null;
    public Scanner sc = new Scanner(System.in);
    public PrintStream ps = null;
    public boolean flag = true;

    public B() throws Exception {
        client = new Socket("localhost", 8888);
        ps = new PrintStream(client.getOutputStream());
        System.out.println("客户端连入端口号为8888的服务端");

        while (flag) {
            String str = sc.nextLine();

            if ("bye".equals(str)) {
                ps.println(str);
                A.flag = false;    //结果这里并没有成功更改A类的静态属性，为何？
                flag = false;
            } else {
                ps.println(str);
            }
        }

        ps.close();
        client.close();
    }
}

public class Test24 {
    public static void main(String[] args) throws Exception {
        //new A();//先运行A
                //new B();//在运行B
    }
}

應該把A放在無限循環中否則執行完之後直接退出並沒有對B的改變做出反應