Java Hashtable keys() Method

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Description

The Java Hashtable keys() method is used to get an enumeration of the keys in this hashtable.

Declaration

Following is the declaration for java.util.Hashtable.keys() method.

public Enumeration<K> keys()

Parameters

NA

Return Value

The method call returns an enumeration of the keys in this hashtable.

Exception

NA

Getting Enumeration of Keys of a HashTable of Integer, Integer Pair Example

The following example shows the usage of Java Hashtable keys() method to iterate over the keys of a Hashtable using Enumeration. We've created a Hashtable object of Integer,Integer pairs. Then few entries are added. An enumeration is retrieved using keys() method and then it is iterated to print the keys of the hashtable.

package com.tutorialspoint;

import java.util.Enumeration;
import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,Integer> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, 1);
      hashtable.put(2, 2);
      hashtable.put(3, 3); 

      Enumeration<Integer> enumeration = hashtable.keys();
      
      while(enumeration.hasMoreElements()) {
         System.out.println(enumeration.nextElement());
      }
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

3
2
1

Getting Enumeration of Keys of a HashTable of Integer, String Pair Example

The following example shows the usage of Java Hashtable keys() method to iterate over the keys of a Hashtable using Enumeration. We've created a Hashtable object of Integer,String pairs. Then few entries are added. An enumeration is retrieved using keys() method and then it is iterated to print the keys of the hashtable.

package com.tutorialspoint;

import java.util.Enumeration;
import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,String> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, "tutorials");
      hashtable.put(2, "point");
      hashtable.put(3, "is best"); 

      Enumeration<Integer> enumeration = hashtable.keys();
      
      while(enumeration.hasMoreElements()) {
         System.out.println(enumeration.nextElement());
      }
   }    
}

Output

Let us compile and run the above program, this will produce the following result.

3
2
1

Getting Enumeration of Keys of a HashTable of Integer, Object Pair Example

The following example shows the usage of Java Hashtable keys() method to iterate over the keys of a Hashtable using Enumeration. We've created a Hashtable object of Integer,Student pairs. Then few entries are added. An enumeration is retrieved using keys() method and then it is iterated to print the keys of the hashtable.

package com.tutorialspoint;

import java.util.Enumeration;
import java.util.Hashtable;

public class HashtableDemo {
   public static void main(String args[]) {
      
      // create hash table
      Hashtable<Integer,Student> hashtable = new Hashtable<>();

      // populate hash table
      hashtable.put(1, new Student(1, "Julie"));
      hashtable.put(2, new Student(2, "Robert"));
      hashtable.put(3, new Student(3, "Adam"));

      Enumeration<Integer> enumeration = hashtable.keys();
      
      while(enumeration.hasMoreElements()) {
         System.out.println(enumeration.nextElement());
      } 
   }    
}
class Student {
   int rollNo;
   String name;

   Student(int rollNo, String name){
      this.rollNo = rollNo;
      this.name = name;
   }

   @Override
   public String toString() {
      return "[ " + this.rollNo + ", " + this.name + " ]";
   }
   @Override
   public boolean equals(Object obj) {
      if(obj == null) return false;
      Student s = (Student)obj;
      return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name);
   }
}

Output

Let us compile and run the above program, this will produce the following result.

3
2
1