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    Java中Hashtable类的java.util.Hashtable.keys()方法用于获取哈希表中存在的键的枚举。

    句法:

    Enumeration enu = Hash_table.keys()

    参数:该方法不接受任何参数。

    返回值:该方法返回Hashtable键的枚举。

    下面的程序用于说明java.util.Hashtable.keys()方法的工作原理:

    程序1:

    // Java code to illustrate the keys() method
    import java.util.*;
     
    public class Hash_Table_Demo {
        public static void main(String[] args)
        {
     
            // Creating an empty Hashtable
            Hashtable<Integer, String> hash_table = 
                             new Hashtable<Integer, String>(); 
     
            // Inserting elements into the table
            hash_table.put(10, "Geeks");
            hash_table.put(15, "4");
            hash_table.put(20, "Geeks");
            hash_table.put(25, "Welcomes");
            hash_table.put(30, "You");
     
            // Displaying the Hashtable
            System.out.println("The Table is: " + hash_table);
     
            // Creating an empty enumeration to store
            Enumeration enu = hash_table.keys();
     
            System.out.println("The enumeration of keys are:");
     
            // Displaying the Enumeration
            while (enu.hasMoreElements()) {
                System.out.println(enu.nextElement());
            }
        }
    }
    

    输出:

    The Table is: {10=Geeks, 20=Geeks, 30=You, 15=4, 25=Welcomes}
    The enumeration of keys are:
    10
    20
    30
    15
    25

    程序2:

    // Java code to illustrate the keys() method
    import java.util.*;
     
    public class Hash_Table_Demo {
        public static void main(String[] args)
        {
     
            // Creating an empty Hashtable
            Hashtable<String, Integer> hash_table = 
                             new Hashtable<String, Integer>(); 
     
            // Inserting elements into the table
            hash_table.put("Geeks", 10);
            hash_table.put("4", 15);
            hash_table.put("Geeks", 20);
            hash_table.put("Welcomes", 25);
            hash_table.put("You", 30);
     
            // Displaying the Hashtable
            System.out.println("The Table is: " + hash_table);
     
            // Creating an empty enumeration to store
            Enumeration enu = hash_table.keys();
     
            System.out.println("The enumeration of keys are:");
     
            // Displaying the Enumeration
            while (enu.hasMoreElements()) {
                System.out.println(enu.nextElement());
            }
        }
    }
    

    输出:

    The Table is: {You=30, Welcomes=25, 4=15, Geeks=20}
    The enumeration of keys are:
    You
    Welcomes
    4
    Geeks

     
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