About the thread safety of containers

1, Summary: https://www.cnblogs.com/cgy-home/p/11184124.html

• Thread-safe collection objects:

Vector

HashTable

StringBuffer (? About StringBuffer thread safety, StringBuilder thread is not safe , the essence is whether the append method is synchronized)

ConcurrentHashMap

• Non-thread-safe collection objects:

ArrayList 

LinkedList

HashMap

HashSet

TreeMap

TreeSet

StringBulider

2. Detailed explanation of the principle: Are all operations of a synchronized container necessarily thread-safe?