The implementation of hash table in Java class Library--hashset

HashSet is implemented based on the implementation--hashmap of the hash table in the Java class Library, unlike HashMap, which holds a single element instead of a key-value pair.

In HashSet, use HashMap to store elements:

private transient hashmap<e,object> map;

As seen from this map type, it stores the hashset element as a HashMap key. Because the value position of the key-value pair is empty, a value is used to occupy the position of the value of the key-value pair:

Private static Final Object PRESENT = new Object ();

present is set to static so that it belongs to a class so that all HashSet instances use this object to save storage space.

Let's take a look at some of the operations in HashSet.

(1) Add an element to the HashSet

    Public boolean Add (E e) {        return Map.put (E, PRESENT) ==null;    }

The put method of HashMap is already mentioned in the implementation--hashmap of the hash table in the Java class Library.

(2) Removing an element from the HashSet

    public boolean remove (Object o) {        return Map.Remove (o) ==present;    }

The Remove method of HashMap is also mentioned in the implementation--hashmap of the hash table in the Java class Library .
(3) See if HashSet contains an element

    Public Boolean contains (Object o) {        return Map.containskey (o);    }

The ContainsKey method of HashMap is also mentioned in the implementation--hashmap of the hash table in the Java class Library .

The implementation of hash table in Java class Library--hashset