這是一個在併發狀態下對共享資源的多執行緒訪問。這些訪問必須是互斥的進行，因為涉及到對資源的修改。假設現在銷售火車票。目的地有3個，分別是北京，天津和上海。使用一個列舉型別表示。
Destation.java

package com.zj.tickets;

 

public enum Destation {

    BEIJING, SHANGHAI, TIANJING

}
下面設計車票類，final int original表示車票基數；int current表示當前還有多少張票；Destation destation表示目的地，它必須從上面的列舉型中取出其一。
Ticket.java

package com.zj.tickets;

 

public class Ticket {

    private final int original;

    private int current;

    private final Destation destation;

 

    public Ticket(int nums, Destation
where) {

       current = original = nums;

       destation = where;

    }

 

    public int degress() {

       return —current;

    }

 

    public int original() {

       return original;

    }

 

    public boolean soldout() {

       return current <= 0;

    }

 

    public Destation getDestation() {

       return destation;

    }

 

    public int getCurrent() {

       return current;

    }

}
下面設計售票廳類，Map<Destation,
Ticket> tickets表示目前可銷售的車票種類，它通過一個static塊初始化。Map<Destation, Integer> records是當前售票廳的火車票銷售情況。List<BookingOffice>
offices表示當前可工作的所有售票廳，每個售票廳是一個執行緒。int ticketsSold表示當前售票廳售出的火車票總數。int id表示當前售票廳編號。
每個執行緒都會模擬客戶買票、工作人員查詢資料庫和售票交易過程。
模擬的資料為，當前發往北京、上海和天津的火車票各5張；每個售票廳交易5次（無論交易成功或失敗）後關閉。
BookingOffice.java

package com.zj.tickets;

import java.util.ArrayList;

import java.util.HashMap;

import java.util.List;

import java.util.Map;

import java.util.Random;

import
java.util.concurrent.TimeUnit;

 

public class BookingOffice implements Runnable {

    private static Map<Destation, Ticket>
tickets = new HashMap<Destation, Ticket>();

    private Map<Destation,
Integer> records;

    private static List<BookingOffice> offices = new
ArrayList<BookingOffice>();

    private int ticketsSold = 0;

    private final int id;

 

    // now
today`s tickets for sell:

    static {

       tickets.put(Destation.BEIJING, new Ticket(5,
Destation.BEIJING));

       tickets.put(Destation.SHANGHAI, new Ticket(5,
Destation.SHANGHAI));

       tickets.put(Destation.TIANJING, new Ticket(5,
Destation.TIANJING));

    }

 

    public BookingOffice(int id) {

       this.id = id;

       offices.add(this);

       resetRecords();

    }

 

    private void resetRecords() {

       records = new HashMap<Destation, Integer>();

    }

 

    private void addRecords(Destation d) {

       Integer freq = records.get(d);

       records.put(d, freq == null ? 1 : freq + 1);

    }

 

    public void run() {

       int transaction = 5;

       while (transaction– > 0) {

           // simulate a customer`s coming:

           Destation d = Destation.values()[new
Random().nextInt(Destation

                  .values().length)];

           print(this + “i want a ticket for “ + d);

           // simulate the officer`s checking:

           try {

              TimeUnit.SECONDS.sleep(1);

           } catch (InterruptedException e) {

              e.printStackTrace();

           }

           // simulate the transaction:

           Ticket wanted = tickets.get(d);

           synchronized (wanted) {

              if (!wanted.soldout()) {

                  print(this + “sold a ticket for “ + d);

                  wanted.degress();

                  addRecords(d);

                  ++ticketsSold;

                  print(this + “” + d + ” tickets still have “

                         + wanted.getCurrent());

              } else

                  print(this + “tickets for “ + d + ” have been sold out.”);

           }

       }

       print(this + “closed”);

       print(this + “totally sold tickets:” + ticketsSold + “,sell
records:”

              + records);

    }

 

    public synchronized int getValue() {

       return ticketsSold;

    }

 

    public String toString() {

       return “<Officce-“ + id + “>”;

    }

 

    static void print(String s) {

       System.out.println(s);

    }

}
模擬售票過程如下，啟動5個售票廳。
Sell.java

package com.zj.tickets;

import java.util.concurrent.ExecutorService;

import java.util.concurrent.Executors;

 

public class Sell {

    public static void main(String[] args) throws Exception
{

       ExecutorService exec = Executors.newCachedThreadPool();

       for (int i = 0; i < 5; i++)

           exec.execute(new
BookingOffice(i));

       exec.shutdown();

    }

}
結果：
<Officce-0>i want a
ticket for BEIJING

<Officce-1>i want a
ticket for SHANGHAI

<Officce-2>i want a
ticket for TIANJING

<Officce-3>i want a
ticket for SHANGHAI

<Officce-4>i want a
ticket for SHANGHAI

<Officce-0>sold a ticket
for BEIJING

<Officce-0>BEIJING tickets still
have 4

<Officce-0>i want a
ticket for TIANJING

<Officce-1>sold a ticket
for SHANGHAI

<Officce-1>SHANGHAI tickets still
have 4

<Officce-1>i want a
ticket for SHANGHAI

<Officce-2>sold a ticket
for TIANJING

<Officce-2>TIANJING
tickets still have 4

<Officce-2>i want a
ticket for BEIJING

<Officce-3>sold a ticket
for SHANGHAI

<Officce-3>SHANGHAI tickets still
have 3

<Officce-3>i want a
ticket for TIANJING

<Officce-4>sold a ticket
for SHANGHAI

<Officce-4>SHANGHAI tickets still
have 2

<Officce-4>i want a
ticket for BEIJING

<Officce-4>sold a ticket
for BEIJING

<Officce-4>BEIJING tickets still
have 3

<Officce-4>i want a
ticket for SHANGHAI

<Officce-3>sold a ticket
for TIANJING

<Officce-3>TIANJING
tickets still have 3

<Officce-3>i want a
ticket for TIANJING

<Officce-2>sold a ticket
for BEIJING

<Officce-2>BEIJING tickets still
have 2

<Officce-2>i want a
ticket for BEIJING

<Officce-1>sold a ticket
for SHANGHAI

<Officce-1>SHANGHAI tickets still
have 1

<Officce-1>i want a
ticket for SHANGHAI

<Officce-0>sold a ticket
for TIANJING

<Officce-0>TIANJING
tickets still have 2

<Officce-0>i want a
ticket for SHANGHAI

<Officce-4>sold a ticket
for SHANGHAI

<Officce-4>SHANGHAI tickets still
have 0

<Officce-4>i want a
ticket for BEIJING

<Officce-3>sold a ticket
for TIANJING

<Officce-3>TIANJING
tickets still have 1

<Officce-3>i want a
ticket for BEIJING

<Officce-2>sold a ticket
for BEIJING

<Officce-2>BEIJING tickets still
have 1

<Officce-2>i want a
ticket for SHANGHAI

<Officce-1>tickets for SHANGHAI have been sold
out.

<Officce-1>i want a
ticket for SHANGHAI

<Officce-0>tickets for SHANGHAI have been sold
out.

<Officce-0>i want a
ticket for SHANGHAI

<Officce-4>sold a ticket
for BEIJING

<Officce-4>BEIJING tickets still
have 0

<Officce-4>i want a
ticket for BEIJING

<Officce-3>tickets for BEIJING have been sold
out.

<Officce-3>i want a
ticket for BEIJING

<Officce-2>tickets for SHANGHAI have been sold
out.

<Officce-2>i want a
ticket for SHANGHAI

<Officce-1>tickets for SHANGHAI have been sold
out.

<Officce-1>i want a
ticket for BEIJING

<Officce-0>tickets for SHANGHAI have been sold
out.

<Officce-0>i want a
ticket for SHANGHAI

<Officce-4>tickets for BEIJING have been sold
out.

<Officce-4>closed

<Officce-4>totally sold
tickets:4,sell records:{BEIJING=2, SHANGHAI=2}

<Officce-3>tickets for BEIJING have been sold
out.

<Officce-3>closed

<Officce-3>totally sold
tickets:3,sell records:{TIANJING=2, SHANGHAI=1}

<Officce-2>tickets for SHANGHAI have been sold
out.

<Officce-2>closed

<Officce-2>totally sold
tickets:3,sell records:{BEIJING=2,
TIANJING=1}

<Officce-1>tickets for BEIJING have been sold
out.

<Officce-1>closed

<Officce-1>totally sold
tickets:2,sell records:{SHANGHAI=2}

<Officce-0>tickets for SHANGHAI have been sold
out.

<Officce-0>closed

<Officce-0>totally sold
tickets:2,sell records:{BEIJING=1,
TIANJING=1}