SortedSet简介
- 我们知道集合set是不要求元素的顺序的，Set访问元素的顺序和存入元素的顺序和时间都是无关的，而SortedSet接口在Set接口的基础上进一步提供了“顺序”的概念，可使得实现SortedSet接口的集合（Set）类,可以“顺序”访问；
- 这里“顺序”的可以是自然数顺序，可以是元素加入的先后顺序，可以是自定义的顺序。
SortedSet UML
SortedSet源码
package java.util;
* <p>All elements inserted into a sorted set must implement the <tt>Comparable</tt>
* interface (or be accepted by the specified comparator). Furthermore, all
* such elements must be <i>mutually comparable</i>: <tt>e1.compareTo(e2)</tt>
* (or <tt>comparator.compare(e1, e2)</tt>) must not throw a
* <tt>ClassCastException</tt> for any elements <tt>e1</tt> and <tt>e2</tt> in
* the sorted set. Attempts to violate this restriction will cause the
* offending method or constructor invocation to throw a
* <tt>ClassCastException</tt>.
*
* <p>Note that the ordering maintained by a sorted set (whether or not an
* explicit comparator is provided) must be <i>consistent with equals</i> if
* the sorted set is to correctly implement the <tt>Set</tt> interface. (See
* the <tt>Comparable</tt> interface or <tt>Comparator</tt> interface for a
* precise definition of <i>consistent with equals</i>.) This is so because
* the <tt>Set</tt> interface is defined in terms of the <tt>equals</tt>
* operation, but a sorted set performs all element comparisons using its
* <tt>compareTo</tt> (or <tt>compare</tt>) method, so two elements that are
* deemed equal by this method are, from the standpoint of the sorted set,
* equal. The behavior of a sorted set <i>is</i> well-defined even if its
* ordering is inconsistent with equals; it just fails to obey the general
* contract of the <tt>Set</tt> interface.
*
* <p>All general-purpose sorted set implementation classes should
* provide four "standard" constructors: 1) A void (no arguments)
* constructor, which creates an empty sorted set sorted according to
* the natural ordering of its elements. 2) A constructor with a
* single argument of type <tt>Comparator</tt>, which creates an empty
* sorted set sorted according to the specified comparator. 3) A
* constructor with a single argument of type <tt>Collection</tt>,
* which creates a new sorted set with the same elements as its
* argument, sorted according to the natural ordering of the elements.
* 4) A constructor with a single argument of type <tt>SortedSet</tt>,
* which creates a new sorted set with the same elements and the same
* ordering as the input sorted set. There is no way to enforce this
* recommendation, as interfaces cannot contain constructors.
*
* <p>Note: several methods return subsets with restricted ranges.
* Such ranges are <i>half-open</i>, that is, they include their low
* endpoint but not their high endpoint (where applicable).
* If you need a <i>closed range</i> (which includes both endpoints), and
* the element type allows for calculation of the successor of a given
* value, merely request the subrange from <tt>lowEndpoint</tt> to
* <tt>successor(highEndpoint)</tt>. For example, suppose that <tt>s</tt>
* is a sorted set of strings. The following idiom obtains a view
* containing all of the strings in <tt>s</tt> from <tt>low</tt> to
* <tt>high</tt>, inclusive:<pre>
* SortedSet<String> sub = s.subSet(low, high+" ");</pre>
*
* A similar technique can be used to generate an <i>open range</i> (which
* contains neither endpoint). The following idiom obtains a view
* containing all of the Strings in <tt>s</tt> from <tt>low</tt> to
* <tt>high</tt>, exclusive:<pre>
* SortedSet<String> sub = s.subSet(low+" ", high);</pre>
*
* <p>This interface is a member of the
* <a href="{@docRoot}/../technotes/guides/collections/index.html">
* Java Collections Framework</a>.
*
* @param <E> the type of elements maintained by this set
*
* @author Josh Bloch
* @see Set
* @see TreeSet
* @see SortedMap
* @see Collection
* @see Comparable
* @see Comparator
* @see ClassCastException
* @since 1.2
*/
public interface SortedSet<E> extends Set<E> {
// 实现接口的API约定：返回用于集合set排序的比较器，如果集合set使用Comparable的元素的自然排序，返回nul
Comparator<? super E> comparator();
// 返回集合set的子集合（称为视图）：从集合set的fromElement到toElement，包含fromElement,不含toElement,简称前闭后开
// 若 fromElement 等于 toElement,返回空集合
// 对视图结构的修改直接反映在父集合set上
// 对视图集合不合理的索引范围操作，会抛出IllegalArgumentException，
// fromElement toElement不可和集合Set中的元素比较，会抛出ClassCastException
// fromElement或toElement为null,但是集合set不可放null,会抛出NullPointerException
SortedSet<E> subSet(E fromElement, E toElement);
/**
* Returns a view of the portion of this set whose elements are
* strictly less than <tt>toElement</tt>. The returned set is
* backed by this set, so changes in the returned set are
* reflected in this set, and vice-versa. The returned set
* supports all optional set operations that this set supports.
*
* <p>The returned set will throw an <tt>IllegalArgumentException</tt>
* on an attempt to insert an element outside its range.
*
* @param toElement high endpoint (exclusive) of the returned set
* @return a view of the portion of this set whose elements are strictly
* less than <tt>toElement</tt>
* @throws ClassCastException if <tt>toElement</tt> is not compatible
* with this set's comparator (or, if the set has no comparator,
* if <tt>toElement</tt> does not implement {@link Comparable}).
* Implementations may, but are not required to, throw this
* exception if <tt>toElement</tt> cannot be compared to elements
* currently in the set.
* @throws NullPointerException if <tt>toElement</tt> is null and
* this set does not permit null elements
* @throws IllegalArgumentException if this set itself has a
* restricted range, and <tt>toElement</tt> lies outside the
* bounds of the range
*/
//
SortedSet<E> headSet(E toElement);
/**
* Returns a view of the portion of this set whose elements are
* greater than or equal to <tt>fromElement</tt>. The returned
* set is backed by this set, so changes in the returned set are
* reflected in this set, and vice-versa. The returned set
* supports all optional set operations that this set supports.
*
* <p>The returned set will throw an <tt>IllegalArgumentException</tt>
* on an attempt to insert an element outside its range.
*
* @param fromElement low endpoint (inclusive) of the returned set
* @return a view of the portion of this set whose elements are greater
* than or equal to <tt>fromElement</tt>
* @throws ClassCastException if <tt>fromElement</tt> is not compatible
* with this set's comparator (or, if the set has no comparator,
* if <tt>fromElement</tt> does not implement {@link Comparable}).
* Implementations may, but are not required to, throw this
* exception if <tt>fromElement</tt> cannot be compared to elements
* currently in the set.
* @throws NullPointerException if <tt>fromElement</tt> is null
* and this set does not permit null elements
* @throws IllegalArgumentException if this set itself has a
* restricted range, and <tt>fromElement</tt> lies outside the
* bounds of the range
*/
SortedSet<E> tailSet(E fromElement);
/**
* Returns the first (lowest) element currently in this set.
*
* @return the first (lowest) element currently in this set
* @throws NoSuchElementException if this set is empty
*/
E first();
/**
* Returns the last (highest) element currently in this set.
*
* @return the last (highest) element currently in this set
* @throws NoSuchElementException if this set is empty
*/
E last();
/**
* Creates a {@code Spliterator} over the elements in this sorted set.
*
* <p>The {@code Spliterator} reports {@link Spliterator#DISTINCT},
* {@link Spliterator#SORTED} and {@link Spliterator#ORDERED}.
* Implementations should document the reporting of additional
* characteristic values.
*
* <p>The spliterator's comparator (see
* {@link java.util.Spliterator#getComparator()}) must be {@code null} if
* the sorted set's comparator (see {@link #comparator()}) is {@code null}.
* Otherwise, the spliterator's comparator must be the same as or impose the
* same total ordering as the sorted set's comparator.
*
* @implSpec
* The default implementation creates a
* <em><a href="Spliterator.html#binding">late-binding</a></em> spliterator
* from the sorted set's {@code Iterator}. The spliterator inherits the
* <em>fail-fast</em> properties of the set's iterator. The
* spliterator's comparator is the same as the sorted set's comparator.
* <p>
* The created {@code Spliterator} additionally reports
* {@link Spliterator#SIZED}.
*
* @implNote
* The created {@code Spliterator} additionally reports
* {@link Spliterator#SUBSIZED}.
*
* @return a {@code Spliterator} over the elements in this sorted set
* @since 1.8
*/
@Override
default Spliterator<E> spliterator() {
return new Spliterators.IteratorSpliterator<E>(
this, Spliterator.DISTINCT | Spliterator.SORTED | Spliterator.ORDERED) {
@Override
public Comparator<? super E> getComparator() {
return SortedSet.this.comparator();
}
};
}
}