java模拟实现机场过安检处理流程-mile米乐体育
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
1flightsecurity
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 "]"; } }
2fightsecuritytest
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://www.cppcns.comngpass; } @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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