Java TreeMap size()方法及示例

TreeMap类的size()方法用于获取Map的大小，它指的是Map中的键值对或映射的数量。

--> java.util package
    --> TreeMap class
        --> size() Method   

语法

Tree_Map.size()

返回值： Map的大小，也就是Map中存在的键值对的数量。

例1： 将字符串值映射到整数键上

// Java Program to Illustrate size() Method
// of TreeMap class
 
// Importing required classes
import java.util.*;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Creating an empty TreeMap by
        // declaring object of Integer, string pairs
        TreeMap<Integer, String> tree_map
            = new TreeMap<Integer, String>();
 
        // Mapping string values to int keys
        // using put() method
        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 elements of TreeMap
        System.out.println("Initial Mappings are: "
                           + tree_map);
 
        // Now displaying the size of this map
        // using size() method
        System.out.println("The size of the map is "
                           + tree_map.size());
    }
}

输出

Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
The size of the map is 5

例2： 将整数值映射到字符串键上

// Java Program to Illustrate the size() method
// of TreeMap class
 
// Importing required classes
import java.util.*;
 
// Main class
public class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Creating an empty TreeMap by
        // declaring object of string, integer pairs
        TreeMap<String, Integer> tree_map
            = new TreeMap<String, Integer>();
 
        // Mapping int values to string keys
        // using put() method
        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);
 
        // Printing the elements of TreeMap
        System.out.println("Initial Mappings are: "
                           + tree_map);
 
        // Printing the size of the map
        // using size() method
        System.out.println("The size of the map is "
                           + tree_map.size());
    }
}

输出

Initial Mappings are: {4=15, Geeks=20, Welcomes=25, You=30}
The size of the map is 4

注意： 同样的操作可以通过不同数据类型的变化和组合对任何类型的Mapping进行操作。