Java中的TreeMap lastKey()方法

Java.util.TreeMap.lastKey() 用于检索地图中存在的最后一个或最高的键。

句法：

tree_map.lastKey()

参数：该方法不带任何参数。

返回值：该方法返回地图中存在的最后一个键。

异常：如果地图为空，该方法将抛出NoSuchElementException 。

下面的程序说明了Java.util.TreeMap.lastKey() 方法的工作：
方案一：

// Java code to illustrate the lastKey() method
import java.util.*;
  
public class Tree_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeMap
        TreeMap tree_map = new TreeMap();
  
        // Mapping string values to int keys
        tree_map.put(10, "Geeks");
        tree_map.put(15, "4");
        tree_map.put(20, "Geeks");
        tree_map.put(25, "Welcomes");
        tree_map.put(30, "You");
  
        // Displaying the TreeMap
        System.out.println("The Mappings are: " + tree_map);
  
        // Displaying the lastKey of the map
        System.out.println("The last key is " + tree_map.lastKey());
    }
}

输出：

The Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
The last key is 30

方案二：

// Java code to illustrate the lastKey() method
import java.util.*;
  
public class Tree_Map_Demo {
    public static void main(String[] args)
    {
  
        // Creating an empty TreeMap
        TreeMap tree_map = new TreeMap();
  
        // Mapping int values to string keys
        tree_map.put("Geeks", 10);
        tree_map.put("4", 15);
        tree_map.put("Geeks", 20);
        tree_map.put("Welcomes", 25);
        tree_map.put("You", 30);
  
        // Displaying the TreeMap
        System.out.println("The Mappings are: " + tree_map);
  
        // Displaying the lastKey of the map
        System.out.println("The last key is " + tree_map.lastKey());
    }
}

输出：

The Mappings are: {4=15, Geeks=20, Welcomes=25, You=30}
The last key is You