Java中的 IdentityHashMap size() 方法

IdentityHashMap 类的Java.util.IdentityHashMap.size() 方法用于获取IdentityHashMap 的大小，该大小是指Map 中键值对或映射的数量。

句法：

Identity_Hash_Map.size()

参数：该方法不带任何参数。

返回值：该方法返回映射的大小，这也意味着映射中存在的键值对的数量。

下面的程序说明了Java.util.IdentityHashMap.size() 方法：

程序 1 ：

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

输出：

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

方案二：

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

输出：

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

注意：可以对任何类型的映射执行相同的操作，这些映射具有不同数据类型的变化和组合。