SortedMap接口-Map排序的用法

2015-07-11 15:46:26 暂无评论月上柳梢 Java基础 1,020

SortedMap接口默认使用键值默认顺序或者通过Comparator接口实现对象作为排序依据。：

public interface SortedMap
extends Map； // Map的子接口；
A Map that further provides a total ordering on its keys. The map is ordered according to the natural ordering of its keys, or by a Comparator typically provided at sorted map creation time. This order is reflected when iterating over the sorted map’s collection views (returned by the entrySet, keySet and values methods). Several additional operations are provided to take advantage of the ordering. (This interface is the map analogue of SortedSet.)

// 非继承抽象方法：
Comparator         comparator()
          Returns the comparator used to order the keys in this map, or null if this map uses the natural ordering of its keys.
K         firstKey()        // 返回在当前映射中排序最低的key
          Returns the first (lowest) key currently in this map.
SortedMap         headMap(K toKey)        // 返回当前映射中小于指定key的子映射！
          Returns a view of the portion of this map whose keys are strictly less than toKey.
K         lastKey()        // 返回当前映射中排序最高的key
          Returns the last (highest) key currently in this map.
SortedMap         subMap(K fromKey, K toKey)        // 返回当前映射中介于指定key范围的子映射！
          Returns a view of the portion of this map whose keys range from fromKey, inclusive, to toKey, exclusive.
SortedMap         tailMap(K fromKey)        // 返回当前映射中高于指定key的子映射！
          Returns a view of the portion of this map whose keys are greater than or equal to fromKey.
// 子类：
public class TreeMap
extends AbstractMap
implements NavigableMap, Cloneable, Serializable；
——-应用TreeMap实例化SortedMap：输出指定范围的：
package com.mldn;
import java.util.Map;
import java.util.SortedMap;
import java.util.TreeMap;
public class SortedMapDemo
{
        public static void main(String[] args)
        {
                SortedMap        sort = new TreeMap();        // 实例化排序映射
                sort.put(“A”, “www.k187.com”);        // 放置实体
                sort.put(“B”, “www.baidu.com”);
                sort.put(“C”, “www.sina.com”);
                sort.put(“D”, “www.google.com”);
                sort.put(“E”, “www.yahoo.com”);
                System.out.println(“第一个key：” + sort.firstKey());        // 获取排序最靠前的key
                System.out.println(“最后一个key：” + sort.lastKey());        // 获取排序最靠后的key
                System.out.println(“最后一个key对应的值：” + sort.get(sort.lastKey()));        // 获取值
                // 输出所有小于指定key的实体：<
                System.out.println(“输出所有小于指定key的实体：”);
                for (Map.Entry me : sort.headMap(“C”).entrySet())        // 用foreach输出
                {
                        System.out.println(me.getKey() + “–>” + me.getValue());        // 输出实体
                }
                // 输出所有大于指定key的实体：>=
                System.out.println(“输出所有大于指定key的实体：”);
                for (Map.Entry me : sort.tailMap(“C”).entrySet())        // 用foreach输出
                {
                        System.out.println(me.getKey() + “–>” + me.getValue());        // 输出实体
                }
                // 输出所有介于自定义范围内的实体：>= && <
                System.out.println(“输出所有介于自定义范围内的实体：”);
                for (Map.Entry me : sort.subMap(“B”, “E”).entrySet())        // 用foreach输出
                {
                        System.out.println(me.getKey() + “–>” + me.getValue());        // 输出实体
                }
        }
}
/*
ubuntu@xu-desktop:~$ java com.mldn.SortedMapDemo
第一个key：A
最后一个key：E
最后一个key对应的值：www.yahoo.com
输出所有小于指定key的实体：
A–>www.k187.com
B–>www.baidu.com
输出所有大于指定key的实体：
C–>www.sina.com
D–>www.google.com
E–>www.yahoo.com
输出所有介于自定义范围内的实体：
B–>www.baidu.com
C–>www.sina.com
D–>www.google.com
*/