Java中NavigableMap接口的headMap()方法用于返回此Map的一部分，其键小于(或等于，如果包含，则为true)toKey的map
NavigableMap<K, V> headMap(K toKey,
boolean inclusive)
参数：此函数接受两个参数：
- toKey：此参数指的是 key 。
- inclusive：此参数决定是否将要删除的 key 与相等进行比较。
返回值：返回此Map部分的视图，该视图的键小于(或等于，如果包含在内，则为true)toKey。
程序1：当键为整数且缺少第二个参数时。
// Java code to demonstrate the working of
// headMap?() method
import java.io.*;
import java.util.*;
public class GFG {
public static void main(String[] args)
{
// Declaring the NavigableMap of Integer and String
NavigableMap<Integer, String> nmmp = new TreeMap<>();
// assigning the values in the NavigableMap
// using put()
nmmp.put(2, "two");
nmmp.put(7, "seven");
nmmp.put(3, "three");
System.out.println("View of map with key less than"
+ " or equal to 7 : " + nmmp.headMap(7));
}
}
输出：
View of map with key less than or equal to 7 : {2=two, 3=three}
程序2：带有第二个参数。
// Java code to demonstrate the working of
// headMap?() method
import java.io.*;
import java.util.*;
public class GFG {
public static void main(String[] args)
{
// Declaring the NavigableMap of Integer and String
NavigableMap<Integer, String> nmmp = new TreeMap<>();
// assigning the values in the NavigableMap
// using put()
nmmp.put(2, "two");
nmmp.put(7, "seven");
nmmp.put(3, "three");
nmmp.put(9, "nine");
// headMap with second argument as true
System.out.println("View of map with key less than"
+ " or equal to 7 : " + nmmp.headMap(7, true));
}
}
输出：
View of map with key less than or equal to 7 : {2=two, 3=three, 7=seven}
参考： https://docs.oracle.com/javase/10/docs/api/java/util/NavigableMap.html#headMap(K, boolean)
标签：map,headMap,用法,key,put,NavigableMap,nmmp From： https://www.cnblogs.com/r1-12king/p/18032504