201771010112罗松《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。

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()));// 在指定的毫秒数内让当前正在执行的线程休眠
                    }
                } catch (InterruptedException e) {
                }
            };
            Thread t = new Thread(r);// 分配新的 Thread 对象
            t.start();// 开始线程
        }
    }
}

SynchBankTest

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;
    private Lock bankLock;
    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();// 加锁
        try {
            while (accounts[from] < amount)
                sufficientFunds.await();// 锁对象的条件对象
            System.out.print(Thread.currentThread());// 返回对当前正在执行的线程对象的引用
            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.signalAll();// 唤醒所有等待线程
        } finally {
            bankLock.unlock();// 解锁
        }
    }

    /**
     * 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;
    }
}

Bank

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。

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()));// 在指定的毫秒数内让当前正在执行的线程休眠
                    }
                } catch (InterruptedException e) {
                }
            };
            Thread t = new Thread(r);// 分配新的 Thread 对象
            t.start();// 使线程开始执行
        }
    }
}

SynchBankTest2

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();// 添加一个线程到等待集中
        System.out.print(Thread.currentThread());// 返回对当前正在执行的线程对象的引用
        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());
        notifyAll();// 解除等待线程的阻塞状态
    }

    /**
     * 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;
    }
}

Bank

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();

  }

}

运行结果：

 

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

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;

    @Override
    public void run() {
        // TODO Auto-generated method stub
        while (flag) {
            try {
                Thread.sleep(500);
            } catch (Exception e) {
                // TODO: handle exception
                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;
                }
            }

        }

    }
}

三、实验总结：

 

这次实验比起前几次来说不算难，完成得也比较轻松，接下来的时间主要是复习之前的知识，为期末考试做准备。