Java中的IdentityHashMap size()方法

IdentityHashMap类的java.util.IdentityHashMap.size()方法用于获取IdentityHashMap中键值对或映射的数量。

语法：

Identity_Hash_Map.size()

参数： 该方法不需要任何参数。

返回值： 该方法返回映射中键值对的数量，也就是Map中的映射数量。

以下程序说明了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<Integer, String> identity_hash = new 
                      IdentityHashMap<Integer, String>();

        // 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

程序2: :

// 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<String, Integer> identity_hash = new 
                      IdentityHashMap<String, Integer>();

        // 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： 可以使用不同数据类型的变化和组合执行各种类型映射相同的操作。