通过阅读源码发现，HashSet底层的实现源码其实就是调用HashMap的方法实现的，所以如果你阅读过HashMap或对HashMap比较熟悉的话，那么阅读HashSet就很轻松，也很容易理解了。我之前也写了一篇关于hashMap源码阅读的文章，可以点击这里查看。

使用过HashSet的都清楚它保存的元素是不可以重复的，其实HashSet的元素都是保存在HashMap的key中的，而HashMap的key是没有重复的。

构造函数

/**

* Constructs a new, empty set; the backing HashMap instance has

* the specified initial capacity and the specified load factor.

*

* @param initialCapacity the initial capacity of the hash map

* @param loadFactor the load factor of the hash map

* @throws IllegalArgumentException if the initial capacity is less

* than zero, or if the load factor is nonpositive

*/

public HashSet(int initialCapacity, float loadFactor) {

map = new HashMap<>(initialCapacity, loadFactor);

}

HashSet的构造方法都是直接调用了HashMap的构造方法，HashSet有很多个构造方法全部都是直接调用了HashMap的构造方法。

add方法

/**

* Adds the specified element to this set if it is not already present.

* More formally, adds the specified element e to this set if

* this set contains no element e2 such that

* (e==null ? e2==null : e.equals(e2)).

* If this set already contains the element, the call leaves the set

* unchanged and returns false.

*

* @param e element to be added to this set

* @return true if this set did not already contain the specified

* element

*/

public boolean add(E e) {

return map.put(e, PRESENT)==null;

}

contains方法

/**

* Returns true if this set contains the specified element.

* More formally, returns true if and only if this set

* contains an element e such that

* (o==null ? e==null : o.equals(e)).

*

* @param o element whose presence in this set is to be tested

* @return true if this set contains the specified element

*/

public boolean contains(Object o) {

return map.containsKey(o);

}

remove方法

/**

* Removes the specified element from this set if it is present.

* More formally, removes an element e such that

* (o==null ? e==null : o.equals(e)),

* if this set contains such an element. Returns true if

* this set contained the element (or equivalently, if this set

* changed as a result of the call). (This set will not contain the

* element once the call returns.)

*

* @param o object to be removed from this set, if present

* @return true if the set contained the specified element

*/

public boolean remove(Object o) {

return map.remove(o)==PRESENT;

}

作者：Java邵先生
链接：https://www.jianshu.com/p/45e01d99cdbe