import java.io.*;
class TestInOut implements Runnable
{
    Process p=null;
    public TestInOut()
    {
        try
        {
            p=Runtime.getRuntime().exec("java MyTest");
            new Thread(this).start();
        }catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    public static void main(String []args)
    {
        TestInOut tio=new TestInOut();
        tio.send();
    }
    public void send()
    {
        //int count=0;
        try
        {
            OutputStream os=p.getOutputStream();
            while(true)
            {
        //        System.out.println(++count);
                os.write("help\r\n".getBytes());
            }
        }catch(Exception e)
        {
            e.printStackTrace();
        }
    }
    public void run()
    {
        try
        {
            InputStream in=p.getInputStream();
            BufferedReader br=new BufferedReader(new InputStreamReader(in));
            while(true)
            {
                String strLine=br.readLine();
                if(strLine!=null)
                System.out.println(strLine);
                else
                return;
            }
        }catch(Exception e)
        {
            e.printStackTrace();
        }
    }
}

import java.io.*;
public class MyTest
{
    public static void main(String []args) throws Exception
    {
        BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
        while(true)
        {
        //    System.out.println("Hi:"+new BufferedReader(new InputStreamReader(System.in)).readLine());//原始状态
        //    String strLine=new BufferedReader(new InputStreamReader(System.in)).readLine();//修改状态
            String strLine=br.readLine();
            if(strLine!=null)
            System.out.println("Hi:"+strLine);
            else
            return;
        }
    }
}

import java.io.*;

public class MyTest {
    public static void main(String[] args) throws Exception {
        //获取控制台的流，包装为BufferedReader，方便正行读取
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        while (true) {
            // System.out.println("Hi:"+new BufferedReader(new
            // InputStreamReader(System.in)).readLine());//原始状态
            // String strLine=new BufferedReader(new
            // InputStreamReader(System.in)).readLine();//修改状态
            
            //控制台中读取一行，返回null表示结束
            String strLine = br.readLine();
            
            //如果没有结束，答应Hi +　输入的信息
            if (strLine != null)
                System.out.println("Hi:" + strLine);
            //否则退出程序
            else
                return;
        }
    }
}

------解决方案--------------------
Java code

import java.io.*;

class TestInOut implements Runnable {
    Process p = null;

    public TestInOut() {
        try {
            // 运行My Test 监听MyTest输入输出
            p = Runtime.getRuntime().exec("java MyTest");
            new Thread(this).start();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        TestInOut tio = new TestInOut();
        tio.send();
    }

    public void send() {
        // int count=0;
        try {
            // 输出流，往My Test循环发送help的信息
            OutputStream os = p.getOutputStream();
            while (true) {
                // System.out.println(++count);
                os.write("help\r\n".getBytes());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public void run() {
        try {
            // 输入流，获取My Test的输出
            InputStream in = p.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(in));
            while (true) {
                String strLine = br.readLine();
                if (strLine != null)
                    System.out.println(strLine);
                else
                    return;
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}