problem:
Exception in thread "main" java.lang.NullPointerException
Screenshot:
the reason:
The error is caused by the NULL value put into HashTable. Although HashTabale has been basically eliminated, I believe that some people will have this problem.
Foreword:
HashMap and HashTable and ConcurrentHashMap are knowledge points that most Java developers have experienced. Today I will talk about the differences, advantages and disadvantages between them.
Comparison chart:
