Java中的 TreeMap ceilingEntry() 和 ceilingKey() 方法

Java.util.TreeMap 中有两个ceilingEntry() 的变体，本文都讨论了这两个变体。

1. ceilingEntry(K Key) ：用于返回一个与大于或等于给定键的最小键关联的键值映射，如果没有该键，则返回null。

Syntax : 
public Map.Entry ceilingEntry(K key)
Parameters : 
key : The key to be matched.
Return Value : 
It returns the entry with the least key greater than or equal to key, and null if 
there is no such key.
Exception : 
ClassCastException : It throws the exception if the specified key cannot be compared
with the keys currently in the map.
NullPointerException : It throws the exception if the specified key is null. 

// Java code to demonstrate the working of 
// ceilingEntry()
  
import java.io.*;
import java.util.*;
  
public class ceilingEntry1 {
      
  public static void main(String[] args) {
   
  // Declaring the tree map of Integer and String
  TreeMap treemap = new TreeMap();
       
  // assigning the values in the tree map
  // using put()
  treemap.put(2, "two");
  treemap.put(7, "seven");
  treemap.put(3, "three");
     
  // Use of ceilingEntry()
  // returns 7=seven ( next greater key-value)
  System.out.println("The next greater key-value of 5 is : " + treemap.ceilingEntry(5));
    
  // returns "null" as no value present
  // greater than or equal to number
  System.out.println("The next greater key-value of 8 is : " + treemap.ceilingEntry(8));
    
  }
}

输出：

The next greater key-value of 5 is : 7=seven
The next greater key-value of 8 is : null

2. ceilingKey(K key) ：这也与上面的相同，但唯一的区别是它不包含映射键。它只是返回大于或等于给定键的最小键，否则返回 NULL。

Syntax : 
public K ceilingKey(K key)
Parameters : 
key : The key to be matched.
Return Value : 
It returns the entry with the least key greater than or equal to key, and null 
if there is no such key.
Exception:
ClassCastException : It throws the exception if the specified key cannot be compared
with the keys currently in the map.
NullPointerException : It throws the exception if the specified key is null. 

// Java code to demonstrate the working of 
// ceilingKey()
  
import java.io.*;
import java.util.*;
  
public class ceilingKey1 {
      
  public static void main(String[] args) {
   
  // Declaring the tree map of Integer and String
  TreeMap treemap = new TreeMap();
       
  // assigning the values in the tree map
  // using put()
  treemap.put(2, "two");
  treemap.put(7, "seven");
  treemap.put(3, "three");
     
  // Use of ceilingKey()
  // returns 7 ( next greater key)
  System.out.println("The next greater key of 5 is : " + treemap.ceilingKey(5));
    
  // returns "null" as no key present
  // greater than or equal to number
  System.out.println("The next greater key of 8 is : " + treemap.ceilingKey(8));
    
  }
}

输出：

The next greater key of 5 is : 7
The next greater key of 8 is : null