summary

HashSet is implemented based on HashMap. The bottom layer uses the key of HashMap to save data, so that the elements are not repeated. Therefore, the implementation of HashSet is relatively simple. Basically, it is completed by directly calling the relevant methods of the bottom HashMap

The construction method of HashSet is to create HashMap:

basic operation

1. Add operation

2. Delete

3. Iterator

Other methods basically call the HashMap method

Because HashSet is implemented based on HashMap, the elements put in should also override the equals and hashcode methods