差异: 关于等级制度: HashSet实现Set。 HashMap实现Map并存储键和值的映射。

在数据库中使用HashSet和HashMap将帮助您理解它们的重要性。 HashSet:通常用于存储唯一的集合对象。 例如:它可以用作存储之间的多对一关系的实现类 class Item和class Bid where (Item有多个投标) HashMap:用于将键映射到值。该值可以为null或Object的任意Object /list (Object本身就是Object)。

HashMap是用来添加、获取、删除…由任何类型的自定义键索引的对象。 HashSet用于添加元素，删除元素，并通过比较它们的哈希值来检查元素是否存在。

HashMap包含元素，HashSet记住它们的哈希值。

顾名思义，HashMap是一个关联Map(从键映射到值)，HashSet只是一个Set。

基本上在HashMap中，用户必须同时提供Key和Value，而在HashSet中只提供Value, Key是通过哈希函数从Value自动派生出来的。因此，在拥有Key和Value之后，HashSet可以在内部存储为HashMap。

HashSet

HashSet class implements the Set interface In HashSet, we store objects(elements or values) e.g. If we have a HashSet of string elements then it could depict a set of HashSet elements: {“Hello”, “Hi”, “Bye”, “Run”} HashSet does not allow duplicate elements that mean you can not store duplicate values in HashSet. HashSet permits to have a single null value. HashSet is not synchronized which means they are not suitable for thread-safe operations until unless synchronized explicitly.[similarity] add contains next notes HashSet O(1) O(1) O(h/n) h is the table

HashMap

HashMap class implements the Map interface HashMap is used for storing key & value pairs. In short, it maintains the mapping of key & value (The HashMap class is roughly equivalent to Hashtable, except that it is unsynchronized and permits nulls.) This is how you could represent HashMap elements if it has integer key and value of String type: e.g. {1->”Hello”, 2->”Hi”, 3->”Bye”, 4->”Run”} HashMap does not allow duplicate keys however it allows having duplicate values. HashMap permits single null key and any number of null values. HashMap is not synchronized which means they are not suitable for thread-safe operations until unless synchronized explicitly.[similarity] get containsKey next Notes HashMap O(1) O(1) O(h/n) h is the table

更多信息请参考这篇文章。

它们之间的主要区别如下:

HashSet

它不允许重复密钥。 即使它不是同步的，这样也会有更好的性能。 它允许一个空键。 当您想要维护一个唯一的列表时，可以使用HashSet。 HashSet实现了Set接口，它是由哈希表(实际上是HashMap实例)支持的。 HashSet存储对象。 HashSet不允许重复元素，但允许空值。 该接口不能保证顺序随时间保持不变。

HashMap

It allows duplicate keys. It is not synchronized, so this will have better performance. HashMap does not maintain insertion order. The order is defined by the Hash function. It is not Thread Safe It allows null for both key and value. It allows one null key and as many null values as you like. HashMap is a Hash table-based implementation of the Map interface. HashMap store object as key and value pair. HashMap does not allow duplicate keys but null keys and values are allowed. Ordering of the element is not guaranteed overtime.