Java NavigableMap ceilingKey()方法

Java中NavigableMap接口的c ceilingKey()方法用于返回大于或等于给定键的最小键，如果不存在这样的键，则返回空。

语法:

K ceilingKey(K key)

其中，K是由这个地图容器维护的键的类型。

参数 ：它接受一个单一的参数Key，它是要被映射的键，是这个集合所接受的键的类型。

返回值 ：它返回大于或等于给定键的最小键，如果没有这样的键存在，则返回空。

以下程序说明了Java中的 ceilingKey() 方法。

程序1 ：当键为整数时。

// Java code to demonstrate the working of
// ceilingKey()  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> tmmp = new TreeMap<>();
  
        // assigning the values in the NavigableMap
        // using put()
        tmmp.put(2, "two");
        tmmp.put(7, "seven");
        tmmp.put(3, "three");
  
        // Use of ceilingKey()
        // returns 7( next greater key)
        System.out.println("The next greater key of 6 is : "
                           + tmmp.ceilingKey(6));
  
        // returns "null" as no value present
        // greater than or equal to number
        System.out.println("The next greater key of 3 is : " 
                                       + tmmp.ceilingKey(3));
    }
}

输出:

The next greater key of 6 is : 7
The next greater key of 3 is : 3

程序2 ：当按键为字符串时。

// Java code to demonstrate the working of
// ceilingKey()  method
  
import java.io.*;
import java.util.*;
  
public class GFG {
  
    public static void main(String[] args)
    {
  
        // Declaring the NavigableMap of Integer and String
        NavigableMap<String, String> tmmp = new TreeMap<>();
  
        // assigning the values in the NavigableMap
        // using put()
        tmmp.put("one", "two");
        tmmp.put("six", "seven");
        tmmp.put("two", "three");
  
        // Use of ceilingKey()
        // returns 7( next greater key)
        System.out.println("The next greater key of five is : "
                           + tmmp.ceilingKey("five"));
  
        // returns "null" as no value present
        // greater than or equal to number
        System.out.println("The next greater key of six is : " + 
                                         tmmp.ceilingKey("six"));
    }
}

输出:

The next greater key of five is : one
The next greater key of six is : six

参考资料 : https://docs.oracle.com/javase/10/docs/api/java/util/NavigableMap.html#ceilingKey(K)