java网络编程错误java.net.ConnectException: Connection refused: connect求教

刚开始学习java网络编程，在书上看到一段代码，就动手试一下，结果出现下面错误：
java.net.ConnectException: Connection refused: connect
源代码如下：
import java.io.*;
import java.net.*;

class lx01 {
public static void main(String[] args) {
String host = "localhost";

    BufferedReader br = null;
    PrintWriter pw = null;
    Socket s = null;

    try {
        s = new Socket(host, 10000);

        InputStreamReader isr;
        isr = new InputStreamReader(s.getInputStream());

        br = new BufferedReader(isr);
        pw = new PrintWriter(s.getOutputStream(), true);

        pw.println("DATE");

        System.out.println(br.readLine());

        pw.println("PAUSE");

        pw.println("DOW");

        System.out.println(br.readLine());

        pw.println("DOM");

        System.out.println(br.readLine());

        pw.println("DOY");

        System.out.println(br.readLine());
    } catch (IOException e) {
        System.out.println(e.toString());
    } finally {
        try {
            if (br != null)
                br.close();

            if (pw != null)
                pw.close();

            if (s != null)
                s.close();
        } catch (IOException e) {
        }
    }
}

}
求教各位大神这是啥原因，如何解决？