Java TreeMap lowerEntry()用法及代码示例

java.util.TreeMap类的lowerEntry()方法用于返回与严格小于给定键的最大键相关联的键-值映射，如果没有这样的键，则返回null

用法:

public Map.Entry lowerEntry(K key)

参数：此方法将 key 作为要为其找到较低条目的参数。

返回值：此方法返回最大键小于键的条目；如果没有这样的键，则返回null。

异常：如果指定键为null且此映射使用自然顺序，或者其比较器不允许使用null键，则此方法将引发NullPointerException。

以下示例说明了lowerEntry()方法

示例1:

// Java program to demonstrate 
// lowerEntry() method 
// for <Integer, String> 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // creating object of TreeMap<Integer, String> 
            TreeMap<Integer, String> 
                treemap = new TreeMap<Integer, String>(); 
  
            // populating tree map 
            treemap.put(1, "One"); 
            treemap.put(2, "Two"); 
            treemap.put(3, "Three"); 
            treemap.put(4, "Four"); 
            treemap.put(5, "Five"); 
  
            // pritnig the TreeMap 
            System.out.println("TreeMap: " + treemap); 
  
            // getting lowerEntry value for 3 
            // using lowerEntry() method 
            Map.Entry<Integer, String> 
                value 
                = treemap.lowerEntry(3); 
  
            // printing the value 
            System.out.println("The lowerEntry value "
                               + " for 3: " + value); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
The lowerEntry value  for 3: 2=Two

示例2:对于NullPointerException

// Java program to demonstrate 
// lowerEntry() method 
// for NullPointerException 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // creating object of TreeMap<Integer, String> 
            TreeMap<Integer, String> 
                treemap = new TreeMap<Integer, String>(); 
  
            // populating tree map 
            treemap.put(1, "One"); 
            treemap.put(2, "Two"); 
            treemap.put(3, "Three"); 
            treemap.put(4, "Four"); 
            treemap.put(5, "Five"); 
  
            // pritnig the TreeMap 
            System.out.println("TreeMap: " + treemap); 
  
            // getting lowerEntry value for null 
            // using lowerEntry() method 
            System.out.println("Trying to get"
                               + " the lowerEntry value"
                               + " for value NULL"); 
  
            Map.Entry<Integer, String> 
                value 
                = treemap.lowerEntry(null); 
  
            // printing the value 
            System.out.println("Value is: " + value); 
        } 
  
        catch (NullPointerException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
}

输出：

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
Trying to get the lowerEntry value for value NULL
Exception thrown : java.lang.NullPointerException

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注：本文由纯净天空筛选整理自RohitPrasad3大神的英文原创作品 TreeMap lowerEntry() method 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。