Java模拟实现机场过安检处理流程

Java模拟实现机场过安检处理流程

目录一 场景描述二 实战三 测试四 问题分析五 说明

一 场景描述

乘飞机时，在进入登机口之前必须经过安全检查，安检口类似于独木桥，每次只能通过一个人，工作人员除了检查你的登机牌外，还有一些其它检查。在此模拟一个非线程安全的安检口类，旅客（线程）分别手持登机牌和身份证接受工作人员的检查。

二 实战

1 FlightSecurity

package concurrent.FlightSecurity;

public class FlightSecurity {

private int count;

// 登机牌

private String boardingPass = "null";

// 身份证

private String idCard = "null";

public void pass(String boardingPass,String idCard){

this.boardingPass = boardingPass;

this.idCard = idCard;

this.count++;

check();

}

private void check() {

// 简单测试，当登机牌和身份证首字母不相同时则表示检查不通过

if(boardingPass.charAt(0)!=idCard.charAt(0)){

throw new RuntimeException("======Excepton======"+toString());

}

}

public String toString(){

return "The " +count +" paaaenges,boardingPass [" + boardingPass + "],idCard [" + idCard +"]";

}

}

2 FightSecurityTest

package concurrent.FlightSecurity;

public class FightSecurityTest {

// 旅客线程

static class Passengers extends Thread{

// 机场安检类

private final FlightSecurity fightSecurity;

// 旅客的身份证

private final String idCard;

// 旅客登机牌

private final String boardingPass;

Passengers(FlightSecurity fightSecurity, String idCard, String boardingPass) {

this.fightSecurity = fightSecurity;

this.idCard = idCard;

this.boardingPass = boardihttp://ngPass;

}

@Override

public void run() {

while(true){

// 旅客不断地过安检

fightSecurity.pass(boardingPass,idCard);

}

}

}

public static void main(String[] args) {

// 定义三个旅客，身份证和登机牌首字母相同

final FlightSecurity flightSecurity= new FlightSecurity();

new Passengers(flightSecurity,"A","A").start();

new Passengers(flightSecurity,"B","B").start();

new Passengers(flightSecurity,"C","C").start();

}

}

三 测试

1 测试结果1

Exception in thread "Thread-1" Exception in thread "Thread-0" java.lang.RuntimeException: ======Excepton======The 356 paaaenges,boardingPass [B],idCard [A]    at concurrent.FlightSecurity.FlightSecurity.check(FlightSecurity.java:20)    at concurrent.FlightSecurity.FlightSecurity.pass(FlightSecurity.java:14)    at concurrent.FlightSecurity.FightSecurityTest$Passengers.run(FightSecurityTest.java:24)java.lang.RuntimeException: ======Excepton======The 356 paaaenges,boardingPass [B],idCard [A]    at concurrent.FlightSecurity.FlightSecurity.check(FlightSecurity.java:20)    at concurrent.FlightSecurity.FlightSecurity.pass(FlightSecurity.java:14)    at concurrent.FlightSecurity.FightSecurityTest$Passengers.run(FightSecurityTest.java:24)

2 测试结果2

Exception in thread "Thread-0" Exception in thread "Thread-1" java.lang.RuntimeException: ======Excepton======The 953 paaaenges,boardingPass [C],idCard [C]    at concurrent.FlightSecurity.FlightSecurity.check(FlightSecurity.java:20)    at concurrent.FlightSecurity.FlightSecurity.pass(FlightSecurity.java:14)    at concurrent.FlightSecurity.FightSecurityTest$Passengers.run(FightSecurityTest.java:24)java.lang.RuntimeException: ======Excepton======The 1039 paaaenges,boardingPass [C],idCard [C]    at concurrent.FlightSecurity.FlightSecurity.check(FlightSecurity.java:20)    at concurrent.FlightSecurity.FlightSecurity.pass(FlightSecurity.java:14)    at concurrent.FlightSecurity.FightSecurityTest$Passengers.run(FightSecurityTest.java:24)

四 问题分析

在多线程情况下调用 pass 方法，虽然参数的传递百分百保证就是这两个值，但是在 pass 方法中对这两个值的赋值很有可能交叉，不能保证原子性操作。

解决的方法是给 pass 方法加上 synchronized 关键字。

public synchronized void pass(String boardingPass,String idCard)

五 说明

在 Java 中经常会听到线程安全的类和线程非安全的类，所谓线程安全的类是指多个线程同时进行操作时，不会引起数据不一致问题，反之则是线程非安全的类，在线程安全的类中经常会看到 synchronized 关键字的身影。

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