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Java TreeMap lowerKey()用法及代码示例


前提条件: Java中的TreeMap

lowerKey()方法用于返回严格小于给定键(作为参数传递)的最大键。用简单的话来说,此方法用于查找作为参数传递的元素之后的下一个最大元素。

用法:


public K TreeMap.lowerKey(K key)

参数:此方法采用强制性参数 key ,这是要匹配的 key 。

返回值:此方法返回的最大 key 严格小于key;如果没有这样的 key ,则返回null。

异常:此方法引发以下异常:

  • ClassCastException:当指定的 key 无法与Map中可用的 key 进行比较时。
  • NullPointerException :当map中指定的键为null且使用自然键时
    排序意味着比较器不允许使用空键。

下面的示例说明了lowerKey()方法的使用:

示例1:

// Java program to demonstrate lowerKey() method 
  
import java.util.TreeMap; 
  
public class FloorKeyDemo { 
    public static void main(String args[]) 
    { 
  
        // create an empty TreeMap 
        TreeMap<Integer, String> 
            numMap = new TreeMap<Integer, String>(); 
  
        // Insert the values 
        numMap.put(6, "Six"); 
        numMap.put(1, "One"); 
        numMap.put(5, "Five"); 
        numMap.put(3, "Three"); 
        numMap.put(8, "Eight"); 
        numMap.put(10, "Ten"); 
  
        // Print the Values of TreeMap 
        System.out.println("TreeMap: " + numMap.toString()); 
  
        // Get the greatest key mapping of the Map 
  
        // As here 9 is not available it returns 8 
        // because 9 is strictly less than 11, present 
        System.out.print("Lower Key Entry of Element 9 is: "); 
        System.out.println(numMap.lowerKey(9)); 
  
        // Though, 3 is available in the Map 
        // it returns 1 because this method returns 
        // strictly less than key according to the specified key 
        System.out.print("Lower Key Entry of Element 3 is: "); 
        System.out.println(numMap.lowerKey(3)); 
    } 
}
输出:
TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Lower Key Entry of Element 9 is: 8
Lower Key Entry of Element 3 is: 1

示例2:演示NullPointerException

// Java program to demonstrate lowerKey() method 
  
import java.util.TreeMap; 
  
public class FloorKeyDemo { 
    public static void main(String args[]) 
    { 
  
        // create an empty TreeMap 
        TreeMap<Integer, String> 
            numMap = new TreeMap<Integer, String>(); 
  
        // Insert the values 
        numMap.put(6, "Six"); 
        numMap.put(1, "One"); 
        numMap.put(5, "Five"); 
        numMap.put(3, "Three"); 
        numMap.put(8, "Eight"); 
        numMap.put(10, "Ten"); 
  
        // Print the Values of TreeMap 
        System.out.println("TreeMap: " + numMap.toString()); 
  
        try { 
            // Passing null as parameter to lowerKey() 
            // This will throw exception 
            System.out.println(numMap.lowerKey(null)); 
        } 
        catch (Exception e) { 
            System.out.println("Exception: " + e); 
        } 
    } 
}
输出:
TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Exception: java.lang.NullPointerException


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注:本文由纯净天空筛选整理自bilal-hungund大神的英文原创作品 TreeMap lowerKey() in Java with Examples。非经特殊声明,原始代码版权归原作者所有,本译文未经允许或授权,请勿转载或复制。