集合:Set
Set集合包含有:EnumSet,SortedSet,HashSet,TreeSet,LinkHashSet,其中treeSet是SortedSet的进一步实现,LinkHashSet是HashSet的进一步实现。
1. EnumSet:EnumSet类是一种专为枚举类设计的集合类,EnumSet中的所有元素都必须是指定枚举类型的枚举值,该枚举类型在创建EnumSe类时显式或隐式的指定。EnumSet的集合元素也是有序的,EnumSet以枚举值在Enum类内的定义顺序来决定集合元素的顺序。
2. SortedSet接口,TreeSet实现类:无序无重复集合(Sorted:按照对象的比较函数对元素排序,而不是指元素的插入次序),由源码可见,底层实现是通过TreeMap的Key值来实现集合无重复元素。
/**
* Constructs a set backed by the specified navigable map.
*/
TreeSet(NavigableMap<E,Object> m) {
this.m = m;
}
/**
* Constructs a new, empty tree set, sorted according to the
* natural ordering of its elements. All elements inserted into
* the set must implement the {@link Comparable} interface.
* Furthermore, all such elements must be <i>mutually
* comparable</i>: {@code e1.compareTo(e2)} must not throw a
* {@code ClassCastException} for any elements {@code e1} and
* {@code e2} in the set. If the user attempts to add an element
* to the set that violates this constraint (for example, the user
* attempts to add a string element to a set whose elements are
* integers), the {@code add} call will throw a
* {@code ClassCastException}.
*/
public TreeSet() {
this(new TreeMap<E,Object>());
}
TreeMap部分源码:元素结构Entry类:链表结构
/**
* Node in the Tree. Doubles as a means to pass key-value pairs back to
* user (see Map.Entry).
*/
static final class Entry<K,V> implements Map.Entry<K,V> {
K key;
V value;
Entry<K,V> left;//左元素
Entry<K,V> right;//右元素
Entry<K,V> parent;//父元素
boolean color = BLACK;
}
3. HashSet:无序无重复集合,由源码可见,底层实现是通过HashMap的Key值来实现集合无序无重复元素,HashMap节点是一个单向链表
4.LinkedHashSet:无序无重复集合,由源码可见,底层实现是通过LinkHashMap(HashMap的进一步实现)的Key值来实现集合无序无重复元素,LinkHashMap节点是一个双向链表。