201771010109焦旭超《面向对象程序设计（java）》第十七周学习总结

1、实验目的与要求

(1) 掌握线程同步的概念及实现技术； 

(2) 线程综合编程练习

2、实验内容和步骤

实验1：测试程序并进行代码注释。

测试程序1：

l 在Elipse环境下调试教材651页程序14-7，结合程序运行结果理解程序；

l 掌握利用锁对象和条件对象实现的多线程同步技术。

代码：

package synch;

import java.util.*;
import java.util.concurrent.locks.*;

/**
 * A bank with a number of bank accounts that uses locks for serializing access.
 * @version 1.30 2004-08-01
 * @author Cay Horstmann
 */
public class Bank
{
   private final double[] accounts;//银行运转的基本数据
   private Lock bankLock;//锁对象
   private Condition sufficientFunds;//

   /**
    * Constructs the bank.
    * @param n the number of accounts
    * @param initialBalance the initial balance for each account
    */
   public Bank(int n, double initialBalance)
   {
      accounts = new double[n];
      Arrays.fill(accounts, initialBalance);
      bankLock = new ReentrantLock();
      sufficientFunds = bankLock.newCondition();
   }

   /**
    * Transfers money from one account to another.
    * @param from the account to transfer from
    * @param to the account to transfer to
    * @param amount the amount to transfer
    */
   public void transfer(int from, int to, double amount) throws InterruptedException
   {
      bankLock.lock();
      try
      {//锁对象的引用条件对象
         while (accounts[from] < amount)
           sufficientFunds.await();
         System.out.print(Thread.currentThread());//打印出线程号
         accounts[from] -= amount;
         System.out.printf(" %10.2f from %d to %d", amount, from, to);
         accounts[to] += amount;
         System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
         sufficientFunds.signal();
      }
      finally
      {
         bankLock.unlock();
      }
   }

   /**
    * Gets the sum of all account balances.
    * @return the total balance
    */
   public double getTotalBalance()
   {
      bankLock.lock();//加锁
      try
      {
         double sum = 0;

         for (double a : accounts)
            sum += a;

         return sum;
      }
      finally
      {
         bankLock.unlock();//解锁
      }
   }

   /**
    * Gets the number of accounts in the bank.
    * @return the number of accounts
    */
   public int size()
   {
      return accounts.length;
   }
}

 

package synch;

/**
 * This program shows how multiple threads can safely access a data structure.
 * @version 1.31 2015-06-21
 * @author Cay Horstmann
 */
public class SynchBankTest
{
   public static final int NACCOUNTS = 100;
   public static final double INITIAL_BALANCE = 1000;
   public static final double MAX_AMOUNT = 1000;
   public static final int DELAY = 10;
   
   public static void main(String[] args)
   {
      Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE);
      for (int i = 0; i < NACCOUNTS; i++)
      {
         int fromAccount = i;
         Runnable r = () -> {
            try
            {
               while (true)
               {
                  int toAccount = (int) (bank.size() * Math.random());
                  double amount = MAX_AMOUNT * Math.random();
                  bank.transfer(fromAccount, toAccount, amount);
                  Thread.sleep((int) (DELAY * Math.random()));
               }
            }
            catch (InterruptedException e)
            {
            }            
         };
         Thread t = new Thread(r);
         t.start();
      }
   }
}

测试程序2：

l 在Elipse环境下调试教材655页程序14-8，结合程序运行结果理解程序；

l 掌握synchronized在多线程同步中的应用。

代码：

package synch2;

import java.util.*;

/**
 * A bank with a number of bank accounts that uses synchronization primitives.
 * @version 1.30 2004-08-01
 * @author Cay Horstmann
 */
public class Bank
{
   private final double[] accounts;

   /**
    * Constructs the bank.
    * @param n the number of accounts
    * @param initialBalance the initial balance for each account
    */
   public Bank(int n, double initialBalance)
   {
      accounts = new double[n];
      Arrays.fill(accounts, initialBalance);
   }

   /**
    * Transfers money from one account to another.
    * @param from the account to transfer from
    * @param to the account to transfer to
    * @param amount the amount to transfer
    */
   public synchronized void transfer(int from, int to, double amount) throws InterruptedException
   {
      while (accounts[from] < amount)
         wait();//导致线程进入等待状态直到它被通知。该方法只能在一个同步方法中调用。
      System.out.print(Thread.currentThread());//打印出线程号
      accounts[from] -= amount;
      System.out.printf(" %10.2f from %d to %d", amount, from, to);//第一个打印结果保留两位小数（最大范围是十位），
      accounts[to] += amount;
      System.out.printf(" Total Balance: %10.2f%n", getTotalBalance());
      notifyAll();//解除那些在该对象上调用wait方法的线程阻塞状态。该方法只能在同步方法或同步块内部调用。
   }

   /**
    * Gets the sum of all account balances.
    * @return the total balance
    */
   public synchronized double getTotalBalance()
   {
      double sum = 0;

      for (double a : accounts)
         sum += a;

      return sum;
   }

   /**
    * Gets the number of accounts in the bank.
    * @return the number of accounts
    */
   public int size()
   {
      return accounts.length;
   }
}

package synch2;

/**
 * This program shows how multiple threads can safely access a data structure,
 * using synchronized methods.
 * @version 1.31 2015-06-21
 * @author Cay Horstmann
 */
public class SynchBankTest2
{
   public static final int NACCOUNTS = 100;
   public static final double INITIAL_BALANCE = 1000;
   public static final double MAX_AMOUNT = 1000;
   public static final int DELAY = 10;

   public static void main(String[] args)
   {
      Bank bank = new Bank(NACCOUNTS, INITIAL_BALANCE);
      for (int i = 0; i < NACCOUNTS; i++)
      {
         int fromAccount = i;
         Runnable r = () -> {
            try
            {
               while (true)
               {
                  int toAccount = (int) (bank.size() * Math.random());
                  double amount = MAX_AMOUNT * Math.random();
                  bank.transfer(fromAccount, toAccount, amount);
                  Thread.sleep((int) (DELAY * Math.random()));
               }
            }
            catch (InterruptedException e)
            {
            }
         };
         Thread t = new Thread(r);
         t.start();
      }
   }
}

测试程序3：

l 在Elipse环境下运行以下程序，结合程序运行结果分析程序存在问题；

l 尝试解决程序中存在问题。

class Cbank {      private static int s=2000;      public   static void sub(int m)      {            int temp=s;            temp=temp-m;           try {      Thread.sleep((int)(1000*Math.random()));    }            catch (InterruptedException e)  {              }           s=temp;           System.out.println("s="+s);   } }     class Customer extends Thread {   public void run()   {    for( int i=1; i<=4; i++)      Cbank.sub(100);     }  } public class Thread3 {  public static void main(String args[])   {    Customer customer1 = new Customer();    Customer customer2 = new Customer();    customer1.start();    customer2.start();   } }

修改后

class Cbank
{
     private static int s=2000;
     public  synchronized  static void sub(int m)
     {
           int temp=s;
           temp=temp-m;
          try {
                 Thread.sleep((int)(1000*Math.random()));
               }
           catch (InterruptedException e)  {              }
              s=temp;
              System.out.println("s="+s);
          }
    }


class Customer extends Thread
{
  public void run()
  {
   for( int i=1; i<=4; i++)
     Cbank.sub(100);
    }
 }
public class Thread3
{
 public static void main(String args[])
  {
   Customer customer1 = new Customer();
   Customer customer2 = new Customer();
   customer1.start();
   customer2.start();
  }
}

实验2 编程练习

利用多线程及同步方法，编写一个程序模拟火车票售票系统，共3个窗口，卖10张票，程序输出结果类似（程序输出不唯一，可以是其他类似结果）。

Thread-0窗口售：第1张票

Thread-0窗口售：第2张票

Thread-1窗口售：第3张票

Thread-2窗口售：第4张票

Thread-2窗口售：第5张票

Thread-1窗口售：第6张票

Thread-0窗口售：第7张票

Thread-2窗口售：第8张票

Thread-1窗口售：第9张票

Thread-0窗口售：第10张票

代码：

package xaincheng;

import java.nio.charset.MalformedInputException;

public class Demo {
    public  static void main(String[] args)
    {
        Mythread mythread=  new  Mythread();
        Thread t1 = new Thread(mythread);
        Thread t2 = new Thread(mythread);
        Thread t3 = new Thread(mythread);
        t1.start();
        t2.start();
        t3.start();
        
    }
    
    
}

class Mythread implements Runnable{
    
    int t=1;
    boolean flag=true;
     
    public void run() {
        
        while(flag) {
            try {
                
                 Thread.sleep(500);
                  }
            catch (InterruptedException e)
            {
                e.printStackTrace();
            }            
            
            
            
             synchronized  (this) {
            
            if(t<=10){
                System.out.println(Thread.currentThread().getName()+"窗口售:第"+t+"张票");
                t++;
            }
            if(t>10){
              flag=false;    
            }
            
        }
        
    }
}
}

实验总结:

　　这周学习的多线程处理技术,相对于前几周实验来说很简单,但是实验本来就是这样,是一个有难到易的过程.等把很多难的东西学过之后再回头发现,这些都很容易.