Java HashSet Collection __java

Java HashSet Collection HashSet Collection

Inherit from Abstractcollection

Implements the Collection interface

The bottom layer uses the HashMap collection to store the elements as keys to the HashMap collection

The iterator invokes the Map.keyset () of the underlying map. iterator

Store unordered, cannot use index to get elements

Element is not repeatable, hash algorithm and Equals method to determine whether the element is repeated, repeat does not add the use method

adding elements

Example

hashset<integer> hs = new hashset<> ();

add Element
Hs.add (a);
Hs.add (a);
System.out.println ("Add (E E):" + HS);

Add a set
//Because the collection itself is added, all elements are duplicated and not added
Hs.addall (HS);
System.out.println ("AddAll" (collection<? Extends e> c): "+ HS";

Run results

removing elements from

Example

hashset<integer> hs = new hashset<> ();
for (int i = 1; I <= 5; i++) {
    hs.add (i);
}

Hs.remove (Integer.valueof (3));
System.out.println ("Remove (Object O):" + HS);

Remove intersection element
//RemoveAll (collection<?> C)

Run results

Judge related

Example

hashset<integer> hs = new hashset<> ();
for (int i = 1; I <= 5; i++) {
    hs.add (i);
}

Determines whether the collection contains the specified element
boolean result = Hs.contains (integer.valueof (3));
System.out.println ("contains (Object o)" + result);

Determines whether the set is null result
= Hs.isempty ();
System.out.println ("IsEmpty ()" + result);

Operation result
Traverse Collection

Converts the collection to an array, and then iterates through the arrays

Example

hashset<integer> hs = new hashset<> ();
for (int i = 1; I <= 5; i++) {
    hs.add (i);
}

integer[] Array = Hs.toarray (new Integer[hs.size ()));
for (int i = 0; i < Array.Length i++) {
    System.out.println (array[i]);

Run results

foreach (Enhanced for) sample

hashset<integer> hs = new hashset<> ();
for (int i = 1; I <= 5; i++) {
    hs.add (i);
}

integer[] Array = Hs.toarray (new Integer[hs.size ()));
for (int i = 0; i < Array.Length i++) {
    System.out.println (array[i]);

foreach (Enhanced for)

Example

hashset<integer> hs = new hashset<> ();
for (int i = 1; I <= 5; i++) {
    hs.add (i);
}

for (Integer i:hs) {
    System.out.println (i);
}

Run results

Iterator iterator

Example

hashset<integer> hs = new hashset<> ();
for (int i = 1; I <= 5; i++) {
    hs.add (i);
}

Iterator<integer> iterator = Hs.iterator ();

while (Iterator.hasnext ()) {
    System.out.println (Iterator.next ());
}

Run results