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  • 2018-08-28  21:21:35        
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    HashMap类的java.util.HashMap.size()方法用于获取哈希映射HashMap中映射的大小,该映射引用Map中键值对或映射的数量。

    句法:

    Hash_Map.size()

    参数:该方法不接受任何参数。
    返回值:该方法返回映射的大小,这也表示映射中存在的键值对的数量。

    下面的程序说明了java.util.HashMap.size()的工作原理

    HashMap.size()程序1:将字符串值映射到整数键。

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

    输出:

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

    HashMap.size()程序2:将整数值映射到字符串键。

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

    输出:

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

    注意:对于具有不同数据类型的变体和组合的任何类型的映射,都可以执行相同的操作。

     
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