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    Java中的java.util.HashMap.keySet() 方法用于创建哈希映射HashMap中包含的关键元素的集合。它基本上返回键的设置视图,或者我们可以创建一个新的集合并将关键元素存储在其中。

    句法:

    hash_map.keySet()

    参数:该方法不带任何参数。

    返回值:该方法返回一个具有哈希映射键的集合。

    下面的程序用于说明java.util.HashMap.keySet() 的工作方法

    HashMap.keySet() 程序1:将字符串值映射到整数键。

    // Java code to illustrate the keySet() 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);
    
            // Using keySet() to get the set view of keys
            System.out.println("The set is: " + hash_map.keySet());
        }
    }
    

    输出:

    Initial Mappings are: {20=Geeks, 25=Welcomes, 10=Geeks, 30=You, 15=4}
    The set is: [20, 25, 10, 30, 15]

    HashMap.keySet() 程序2:将整数值映射到字符串键。

    // Java code to illustrate the keySet() 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);
    
            // Using keySet() to get the set view of keys
            System.out.println("The set is: " + hash_map.keySet());
        }
    }
    

    输出:

    Initial Mappings are: {4=15, Geeks=20, You=30, Welcomes=25}
    The set is: [4, Geeks, You, Welcomes]

    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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