Java中的字典键（）方法与示例

Java中 Dictionary 类的 keys() 方法用于获取字典中存在的键的枚举。

句法：

Enumeration enu = DICTIONARY.keys()

参数：该方法不带任何参数。

返回值：该方法返回 Dictionary 的键的枚举。

以下程序用于说明Java.util.Dictionary.keys() 方法的工作原理：
方案一：

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

输出：

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

方案二：

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

输出：

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