10、JUC:CopyOnWriteArrayList

其他 2021-02-26 14:51:05 阅读次数: 0

学习过程观看视频：[狂神说Java]
https://www.bilibili.com/video/BV1B7411L7tE?t=194&p=11
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1、常用的ArrayList是存在并发安全问题的

package com.unsafe;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;

/**
 * Created by zjl
 * 2020/11/23
 **/
public class ListTest {
    
    

    public static void main(String[] args) {
    
    

        List<String> list =  new ArrayList<>();

        for (int i = 0; i < 10; i++) {
    
    
            new Thread(()->{
    
    
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

运行结果：报并发修改异常：java.util.ConcurrentModificationException

/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/bin/java "-javaagent:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=53952:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/tools.jar:/Users/zhangjianlong/testCode/JUC-study/target/classes:/Users/zhangjianlong/apache-maven-3.6.3/repository/org/projectlombok/lombok/1.18.8/lombok-1.18.8.jar com.unsafe.ListTest
[null, null, 53ab6, ebf87, a3254, 9b84b]
[null, null, 53ab6, ebf87, a3254, 9b84b, 79924, fea34, 9ee15, c6154]
[null, null, 53ab6, ebf87, a3254, 9b84b, 79924, fea34, 9ee15]
[null, null, 53ab6, ebf87, a3254, 9b84b, 79924, fea34]
[null, null, 53ab6, ebf87, a3254, 9b84b, 79924]
[null, null, 53ab6, ebf87, a3254, 9b84b]
Exception in thread "0" Exception in thread "2" Exception in thread "3" Exception in thread "1" java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
	at java.util.ArrayList$Itr.next(ArrayList.java:859)
	at java.util.AbstractCollection.toString(AbstractCollection.java:461)
	at java.lang.String.valueOf(String.java:2994)
	at java.io.PrintStream.println(PrintStream.java:821)
	at com.unsafe.ListTest.lambda$main$0(ListTest.java:20)
	at java.lang.Thread.run(Thread.java:748)
java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
	at java.util.ArrayList$Itr.next(ArrayList.java:859)
	at java.util.AbstractCollection.toString(AbstractCollection.java:461)
	at java.lang.String.valueOf(String.java:2994)
	at java.io.PrintStream.println(PrintStream.java:821)
	at com.unsafe.ListTest.lambda$main$0(ListTest.java:20)
	at java.lang.Thread.run(Thread.java:748)
java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
	at java.util.ArrayList$Itr.next(ArrayList.java:859)
	at java.util.AbstractCollection.toString(AbstractCollection.java:461)
	at java.lang.String.valueOf(String.java:2994)
	at java.io.PrintStream.println(PrintStream.java:821)
	at com.unsafe.ListTest.lambda$main$0(ListTest.java:20)
	at java.lang.Thread.run(Thread.java:748)
java.util.ConcurrentModificationException
	at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:909)
	at java.util.ArrayList$Itr.next(ArrayList.java:859)
	at java.util.AbstractCollection.toString(AbstractCollection.java:461)
	at java.lang.String.valueOf(String.java:2994)
	at java.io.PrintStream.println(PrintStream.java:821)
	at com.unsafe.ListTest.lambda$main$0(ListTest.java:20)
	at java.lang.Thread.run(Thread.java:748)

Process finished with exit code 0

第一种解决方案：使用Vector

package com.unsafe;

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;
import java.util.Vector;

/**
 * Created by zjl
 * 2020/11/23
 **/
public class ListTest {
    
    

    public static void main(String[] args) {
    
    

        List<String> list =  new Vector<>();

        for (int i = 0; i < 10; i++) {
    
    
            new Thread(()->{
    
    
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/bin/java "-javaagent:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=54247:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/tools.jar:/Users/zhangjianlong/testCode/JUC-study/target/classes:/Users/zhangjianlong/apache-maven-3.6.3/repository/org/projectlombok/lombok/1.18.8/lombok-1.18.8.jar com.unsafe.ListTest
[8115c, 975ea, e9704]
[8115c, 975ea, e9704, b106a, 90a5e, a6786, a812b, 36696, 7de1e, a8074]
[8115c, 975ea, e9704, b106a, 90a5e, a6786, a812b, 36696, 7de1e, a8074]
[8115c, 975ea, e9704, b106a, 90a5e, a6786, a812b, 36696]
[8115c, 975ea, e9704, b106a, 90a5e, a6786, a812b, 36696]
[8115c, 975ea, e9704, b106a, 90a5e, a6786, a812b]
[8115c, 975ea, e9704, b106a, 90a5e, a6786, a812b]
[8115c, 975ea, e9704, b106a, 90a5e, a6786]
[8115c, 975ea, e9704, b106a, 90a5e]
[8115c, 975ea, e9704, b106a, 90a5e]

Process finished with exit code 0

第二种解决方案：

Collections.synchronizedList(new ArrayList<>())创建集合。

package com.unsafe;

import java.util.*;

/**
 * Created by zjl
 * 2020/11/23
 **/
public class ListTest {
    
    

    public static void main(String[] args) {
    
    

        List<String> list = Collections.synchronizedList(new ArrayList<>());

        for (int i = 0; i < 10; i++) {
    
    
            new Thread(()->{
    
    
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/bin/java "-javaagent:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=54328:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/tools.jar:/Users/zhangjianlong/testCode/JUC-study/target/classes:/Users/zhangjianlong/apache-maven-3.6.3/repository/org/projectlombok/lombok/1.18.8/lombok-1.18.8.jar com.unsafe.ListTest
[f8702, 5edc6]
[f8702, 5edc6, 874e3, b7fa6, a8312, 39ba9, ce170, 5719e]
[f8702, 5edc6, 874e3, b7fa6, a8312, 39ba9, ce170]
[f8702, 5edc6, 874e3, b7fa6, a8312, 39ba9]
[f8702, 5edc6, 874e3, b7fa6]
[f8702, 5edc6, 874e3, b7fa6]
[f8702, 5edc6, 874e3, b7fa6, a8312]
[f8702, 5edc6]
[f8702, 5edc6, 874e3, b7fa6, a8312, 39ba9, ce170, 5719e, 3fa2a, b3e1b]
[f8702, 5edc6, 874e3, b7fa6, a8312, 39ba9, ce170, 5719e, 3fa2a]

Process finished with exit code 0

第三种解决方案：使用CopyOnWriteArrayList

package com.unsafe;

import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;

/**
 * Created by zjl
 * 2020/11/23
 **/
public class ListTest {
    
    

    public static void main(String[] args) {
    
    

        List<String> list = new CopyOnWriteArrayList();

        for (int i = 0; i < 10; i++) {
    
    
            new Thread(()->{
    
    
                list.add(UUID.randomUUID().toString().substring(0,5));
                System.out.println(list);
            },String.valueOf(i)).start();
        }
    }
}

运行结果：

/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/bin/java "-javaagent:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/lib/idea_rt.jar=55439:/Users/zhangjianlong/Library/Application Support/JetBrains/Toolbox/apps/IDEA-U/ch-0/193.5662.53/IntelliJ IDEA.app/Contents/bin" -Dfile.encoding=UTF-8 -classpath /Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/charsets.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/deploy.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/cldrdata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/dnsns.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jaccess.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/jfxrt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/localedata.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/nashorn.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunec.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunjce_provider.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/sunpkcs11.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/ext/zipfs.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/javaws.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jce.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfr.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jfxswt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/jsse.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/management-agent.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/plugin.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/resources.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/jre/lib/rt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/ant-javafx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/dt.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/javafx-mx.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/jconsole.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/packager.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/sa-jdi.jar:/Library/Java/JavaVirtualMachines/jdk1.8.0_231.jdk/Contents/Home/lib/tools.jar:/Users/zhangjianlong/testCode/JUC-study/target/classes:/Users/zhangjianlong/apache-maven-3.6.3/repository/org/projectlombok/lombok/1.18.8/lombok-1.18.8.jar com.unsafe.ListTest
[01910, 3a4b6]
[01910, 3a4b6, 7ae31, 919f9, ee55e, abfe7, e7625]
[01910, 3a4b6, 7ae31, 919f9, ee55e, abfe7]
[01910, 3a4b6, 7ae31]
[01910, 3a4b6, 7ae31]
[01910, 3a4b6, 7ae31, 919f9, ee55e]
[01910, 3a4b6, 7ae31, 919f9]
[01910, 3a4b6, 7ae31, 919f9, ee55e, abfe7, e7625, 3aa1f, 122f9]
[01910, 3a4b6, 7ae31, 919f9, ee55e, abfe7, e7625, 3aa1f, 122f9, dd2dd]
[01910, 3a4b6, 7ae31, 919f9, ee55e, abfe7, e7625, 3aa1f]

Process finished with exit code 0

附加：为什么CopyOnWriteArrayList比Vector要好呢？

vector的add方法，带有synchronized，会使效率变慢。

  public synchronized boolean add(E e) {
    
    
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
    }

CopyOnWriteArrayList的add方法，使用的是lock锁，效率高。

public boolean add(E e) {
    
    
        final ReentrantLock lock = this.lock;
        lock.lock();
        try {
    
    
            Object[] elements = getArray();
            int len = elements.length;
            Object[] newElements = Arrays.copyOf(elements, len + 1);
            newElements[len] = e;
            setArray(newElements);
            return true;
        } finally {
    
    
            lock.unlock();
        }
    }

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