Java如何使用SortedMap接口？
package org.nhooo.example.util;
import java.util.*;
public class SortedMapDemo {
public static void main(String[] args) {
SortedMap<String, String> sorted = new TreeMap<>();
sorted.put("United States", "New York");
sorted.put("United Kingdom", "London");
sorted.put("Netherlands", "Amsterdam");
sorted.put("Japan", "Tokyo");
sorted.put("France", "Paris");
//获取当前在此映射中的第一个（最低）键
String firstKey = sorted.firstKey();
//获取当前映射中的最后一个（最高）键
String lastKey = sorted.lastKey();
System.out.println("First key: " + firstKey);
System.out.println("Last key : " + lastKey);
//获取此映射范围内其键范围的视图
//从fromKey（日本）（含）到toKey（英国），
//独家。（如果fromKey和toKey相等，则返回
//映射为空。）
SortedMap<String, String> sub = sorted.subMap("Japan",
"United Kingdom");
Set<String> subKeys = sub.keySet();
System.out.println("\nSub Map: ");
System.out.println("============");
for (String key : subKeys) {
System.out.println(key);
}
//获取此映射部分的视图，其键为
//严格小于toKey（在此示例中为荷兰）
SortedMap<String, String> head = sorted.headMap("Netherlands");
Set<String> headKeys = head.keySet();
System.out.println("\nHead Map:");
System.out.println("============");
for (String key : headKeys) {
System.out.println(key);
}
//获取此映射部分的视图，其键为
//严格大于或等于fromKey（在此示例中
//是荷兰）
SortedMap<String, String> tail = sorted.tailMap("Netherlands");
Set<String> tailKeys = tail.keySet();
System.out.println("\nTail Map:");
System.out.println("============");
for (String key : tailKeys) {
System.out.println(key);
}
}
}这是程序的输出：
First key: France Last key : United States Sub Map: ============ Japan Netherlands Head Map: ============ France Japan Tail Map: ============ Netherlands United Kingdom United States