17.11Collection或Map的同步控制

    **   快速报错：**<br />               java容器有一种保护机制，能够防止多个进程同时修改一个容器的内容。对此，java采取快速报错的方式，立刻抛出ConcurrentModficationExcetion异常。<br />   

public class FailFast {
    public static void main(String[] args) {
        Collection<String> c=new ArrayList<>();
        c.add("aaa");
        c.add("bbbb");
        c.add("ccc");
        Iterator<String> iterator = c.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());//在迭代的时候有进行添加
            c.add("fff");
        }
    }
}
public class FailFast {
    public static void main(String[] args) {
        Collection<String> c=new ArrayList<>();
        Iterator<String> iterator = c.iterator();
        c.add("sss");
        System.out.println(iterator.next());
    }
}
OutPut:抛出异常
Exception in thread "main" java.util.ConcurrentModificationException
    at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
    at java.util.ArrayList$Itr.next(ArrayList.java:859)
    at com.package17.FailFast.main(FailFast.java:12)

 上述的两个程序都会引起快速报错，一个是在迭代的时候添加元素，改变了容器的状态，另一个是在容器获得迭代器之后又有元素加入容器，也导致容器的状态不一致。<br />      <br />二、![image.png](https://cdn.nlark.com/yuque/0/2021/png/12862216/1619097716244-9c5feb9f-87ec-41a5-83ff-c0711c9f9d18.png#clientId=ua4b14b63-f65e-4&from=paste&height=18&id=ue1a692e2&name=image.png&originHeight=35&originWidth=857&originalType=binary&size=18798&status=done&style=none&taskId=uea18aa96-a5a2-4e49-879f-94262fb4bcc&width=429)都使用了可以避免快速快速报错的技术<br />          

package com.package17;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.CopyOnWriteArrayList;
import java.util.concurrent.CopyOnWriteArraySet;
public class FailFast {
    public static void main(String[] args) {
        System.out.println("CopyOnWriteArrayList:");
        testList();
        System.out.println("CopyOnWriteArraySet:");
        testSet();
    }
    static void testList(){
        CopyOnWriteArrayList<String> c=new CopyOnWriteArrayList<>();
        c.add("sss");
        c.add("aaa");
        c.add("sccc");
        Iterator<String> iterator = c.iterator();
        while (iterator.hasNext()){
            c.add("123");
            System.out.print(iterator.next()+" ");
        }
        System.out.println(c);
    }
    static void testSet(){
        CopyOnWriteArraySet <String> c=new CopyOnWriteArraySet<>();
        c.add("001");
        c.add("002");
        Iterator<String> iterator = c.iterator();
        while (iterator.hasNext()){
            c.add("123");
            System.out.print(iterator.next()+"  ");
        }
        System.out.println(c);
    }
}
OutPut:
CopyOnWriteArrayList:
sss aaa sccc [sss, aaa, sccc, 123, 123, 123]
CopyOnWriteArraySet:
001  002  [001, 002, 123]