Java Basic Knowledge Hardening Collection Framework note 39:set Collection HashSet store string and traverse

1. Overview of the HashSet class:

(1) No guarantee of Set iteration order

(2) In particular, it does not guarantee that the order is constant

2. How HashSet guarantees element uniqueness

(1) The underlying data structure is a hash table (an array of elements when the list is linked)

(2) Hash table relies on the storage of hashes

(3) Adding a function bottom-up relies on two methods:

• int hashcode ()

• boolean equals (Object obj)

3. HashSet stores strings and iterates through:

(1) The code example is as follows:

1  Packagecn.itcast_02;2 3 ImportJava.util.HashSet;4 5 /*6 * HashSet: Store string and Traverse7  */8  Public classHashsetdemo {9      Public Static voidMain (string[] args) {Ten         //To create a collection object Onehashset<string> HS =NewHashset<string>(); A  -         //Creating and adding elements -Hs.add ("Hello"); theHs.add ("World"); -Hs.add ("Java"); -Hs.add ("World"); -  +         //iterating through the collection -          for(String s:hs) { + System.out.println (s); A         } at     } -}

The results are as follows:

(2) Question: Why are strings stored with the same contents of a string when the strings are stored only one?

Java Basic Knowledge Hardening Collection Framework note 39:set Collection HashSet store string and traverse