Java 中的 SortedMap tailMap()方法

原文:https://www . geesforgeks . org/sorted map-tail map-method-in-Java/

Java 中 SortedMap 接口的 tailMap()方法用于返回该地图中键大于或等于 fromKey 的部分的视图。

The map returned by this method is backed by this map, so the changes of the returned map will be reflected in this map, and vice versa. The map returned by this method supports all optional map operations supported by the map.

注意:如果试图在范围外插入一个键，这个方法返回的地图会抛出一个 IllegalArgumentException。

语法 :

SortedMap<K, V> tailMap(K fromKey)

其中，K 是该集合维护的键的类型，V 是与该键相关联的值的类型。

参数:该函数接受单个参数 fromKey ，表示返回地图中关键点的高端点(不包括)。

返回值:返回该地图中关键点严格大于等于 fromKey 的部分的视图。

异常:

  • [T0】 class castexception 【T1]: If the parameter fromKey is not compatible with the comparator of this map (or if the map has no comparator, if fromkey does not implement compatible).
  • null pointer exception : if the parameter fromkey is null, and the mapping does not allow null keys.
  • [T0】 IllegalArgumentException 【T1]: If the map itself has a restricted range, and from key is in the range.

的边界之外

下面的程序说明了上述方法:

程序 1 :

// A Java program to demonstrate
// working of SortedSet
import java.util.*;

public class Main {
    public static void main(String[] args)
    {
        // Create a TreeSet and inserting elements
        SortedMap<Integer, String> mp = new TreeMap<>();

        // Adding Element to SortedSet
        mp.put(1, "One");
        mp.put(2, "Two");
        mp.put(3, "Three");
        mp.put(4, "Four");
        mp.put(5, "Five");

        // Returning the key greater
        // than or equal to 2
        System.out.print("Last Key in the map is : "
                         + mp.tailMap(2));
    }
}

输出:

Last Key in the map is : {2=Two, 3=Three, 4=Four, 5=Five}

程序二 :

// A Java program to demonstrate
// working of SortedSet
import java.util.*;

public class Main {
    public static void main(String[] args)
    {
        // Create a TreeSet and inserting elements
        SortedMap<String, String> mp = new TreeMap<>();

        // Adding Element to SortedSet
        mp.put("One", "Geeks");
        mp.put("Two", "For");
        mp.put("Three", "Geeks");
        mp.put("Four", "Code");
        mp.put("Five", "It");

        // Returning the key greater
        // than or equal to
        System.out.print("Last Key in the map is : "
                         + mp.tailMap("D"));
    }
}

输出:

Last Key in the map is : {Five=It, Four=Code, One=Geeks, Three=Geeks, Two=For}

参考:https://docs . Oracle . com/javase/10/docs/API/Java/util/sortedmap . html # tail map(K)

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