1.线程安全的集合：集合类中，用于实现线程安全的有两种办法，一种是使用Collections.synchronizedList来替代ArrayList

具体的API如下图：

但是该类会出现并发异常：代码如下

package com.example.demo.juc;import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;public class TestCopyOnWriteArrayList {public static void main(String[] args) {ThreadDemo threadDemo = new ThreadDemo();for (int i = 0; i < 10 ; i++) {new Thread(threadDemo).start();}}
}class ThreadDemo implements Runnable{private static List<String> list = Collections.synchronizedList(new ArrayList<>());{list.add("a");list.add("b");list.add("c");}@Overridepublic void run() {Iterator<String> iterator = list.iterator();while (iterator.hasNext()){iterator.next();list.add("aa");}}
}

异常如下：

java.util.ConcurrentModificationExceptionat java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)at java.util.ArrayList$Itr.next(ArrayList.java:859)at com.example.demo.juc.ThreadDemo.run(TestCopyOnWriteArrayList.java:30)at java.lang.Thread.run(Thread.java:748)

使用第二种方式的CopyOnWriteArrayList不存在该问题,写入并复制，这个每写一个就需要去复制一份，如果添加操作就很多，那就不适合使用这个，如果迭代操作多，则选择该实现

package com.example.demo.juc;import java.util.Iterator;
import java.util.List;
import java.util.concurrent.CopyOnWriteArrayList;public class TestCopyOnWriteArrayList {public static void main(String[] args) {ThreadDemo threadDemo = new ThreadDemo();for (int i = 0; i < 10 ; i++) {new Thread(threadDemo).start();}}
}class ThreadDemo implements Runnable{//    private static List<String> list = Collections.synchronizedList(new ArrayList<>());private static List<String> list = new CopyOnWriteArrayList<>();{list.add("a");list.add("b");list.add("c");}@Overridepublic void run() {Iterator<String> iterator = list.iterator();while (iterator.hasNext()){iterator.next();list.add("aa");}}
}

2.可以使用如下类来：

ConcurrentHashMap替代HashMap
ConcurrentSkipListMap替代TreeMap
ConcurrentSkipListSet替代TreeSet
CopyOnWriteArrayList替代ArrayList
CopyOnWriteArraySet替代HashSet