1、ArraryList

1.1、ArraryList线程不安全演示

import java.util.ArrayList;
import java.util.List;
import java.util.UUID;public class ThreadDemo04 {public static void main(String[] args) {List list = new ArrayList<>();for (int i = 0; i <=10 ; i++) {new Thread(()->{list.add(UUID.randomUUID().toString().substring(0,8));System.out.println(list);},String.valueOf(i)).start();}}

1.2、解决方案

1. 2.1、使用Vector

import java.util.List;
import java.util.UUID;
import java.util.Vector;public class ThreadDemo04 {public static void main(String[] args) {//List list = new ArrayList<>();List list = new Vector<>();for (int i = 0; i <=20 ; i++) {new Thread(()->{list.add(UUID.randomUUID().toString().substring(0,8));System.out.println(list);},String.valueOf(i)).start();}}
}

原理：使用同步关键字 synchronized
源码：

  /*** Adds the specified component to the end of this vector,* increasing its size by one. The capacity of this vector is* increased if its size becomes greater than its capacity.** 
This method is identical in functionality to the* {@link #add(Object) add(E)}* method (which is part of the {@link List} interface).** @param   obj   the component to be added*/public synchronized void addElement(E obj) {modCount++;ensureCapacityHelper(elementCount + 1);elementData[elementCount++] = obj;}

1.2.2、使用Collections

import java.util.*;public class ThreadDemo04 {public static void main(String[] args) {//List list = new ArrayList<>();List list = Collections.synchronizedList(new ArrayList<>());for (int i = 0; i <=20 ; i++) {new Thread(()->{list.add(UUID.randomUUID().toString().substring(0,8));System.out.println(list);},String.valueOf(i)).start();}}
}

1.2.3、使用CopyOnWriteArrayList

import java.util.*;
import java.util.concurrent.CopyOnWriteArrayList;public class ThreadDemo04 {public static void main(String[] args) {//List list = new ArrayList<>();List list = new CopyOnWriteArrayList<>();for (int i = 0; i <=20 ; i++) {new Thread(()->{list.add(UUID.randomUUID().toString().substring(0,8));System.out.println(list);},String.valueOf(i)).start();}}
}

原理：写时复制技术（类似多人签到）
源码：

 /*** Appends the specified element to the end of this list.** @param e element to be appended to this list* @return {@code true} (as specified by {@link Collection#add})*/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();}}

2、HashSet

2.1、HashSet线程不安全演示

import java.util.*;public class ThreadDemo04 {public static void main(String[] args) {Set set = new HashSet<>();for (int i = 0; i <=20 ; i++) {new Thread(()->{set.add(UUID.randomUUID().toString().substring(0,8));System.out.println(set);},String.valueOf(i)).start();}}
}

2.2、解决方案

2.2.1、使用CopyOnWriteArraySet

import java.util.*;
import java.util.concurrent.CopyOnWriteArraySet;

public class ThreadDemo04 {
public static void main(String[] args) {
//Set set = new HashSet<>();
Set set = new CopyOnWriteArraySet<>();
for (int i = 0; i <=20 ; i++) {
new Thread(()->{
set.add(UUID.randomUUID().toString().substring(0,8));
System.out.println(set);
},String.valueOf(i)).start();
}
}
}

3、HashMap

3.1、HashMap线程不安全演示

import java.util.*;public class ThreadDemo04 {public static void main(String[] args) {Map map = new HashMap<>();for (int i = 0; i <=20 ; i++) {String key=String.valueOf(i);new Thread(()->{map.put(key,UUID.randomUUID().toString().substring(0,8));System.out.println(map);},String.valueOf(i)).start();}}
}

3.2、解决方案

3.2.1、使用ConcurrentHashMap

public class ThreadDemo04 {public static void main(String[] args) {//Map map = new HashMap<>();Map map = new ConcurrentHashMap<>();for (int i = 0; i <=20 ; i++) {String key=String.valueOf(i);new Thread(()->{map.put(key,UUID.randomUUID().toString().substring(0,8));System.out.println(map);},String.valueOf(i)).start();}}
}