• Java Data Structures Tutorial

Java Data Structures - Dictionary class

The Dictionary class is an abstract class and it represents a data structure which stores key- value pairs. Each key in this is associated with a value and you can retrieve these values using their respective keys.

Thus, like a map, a dictionary is also could be understood (considered) as a list of key/value pairs.

The Dictionary class in Java

Dictionary is an abstract class that represents a key/value storage repository and operates much like Map.

Given a key and value, you can store the value in a Dictionary object. Once the value is stored, you can retrieve it by using its key. Thus, like a map, a dictionary can be thought of as a list of key/value pairs.

The abstract methods defined by Dictionary are listed below −

Sr.No. Method and Description
1

Enumeration elements( )

Returns an enumeration of the values contained in the dictionary.
2

Object get(Object key)

Returns the object that contains the value associated with the key. If the key is not in the dictionary, a null object is returned.
3

boolean isEmpty( )

Returns true if the dictionary is empty, and returns false if it contains at least one key.
4

Enumeration keys( )

Returns an enumeration of the keys contained in the dictionary.
5

Object put(Object key, Object value)

Inserts a key and its value into the dictionary. Returns null if the key is not already in the dictionary; returns the previous value associated with the key if the key is already in the dictionary.
6

Object remove(Object key)

Removes the key and its value. Returns the value associated with the key. If the key is not in the dictionary, a null is returned.
7

int size( )

Returns the number of entries in the dictionary.

The Dictionary class is obsolete. You should implement the Map interface to obtain key/value storage functionality.

Example

Live Demo 
package com.tutorialspoint;

import java.util.*;

public class DictionaryDemo {
   public static void main(String[] args) {

      // create a new hasthtable
      Dictionary d = new Hashtable();

      // put some elements
      d.put("1", "Chocolate");
      d.put("2", "Cocoa");
      d.put("5", "Coffee");

      // print how many times put was called
     System.out.println("Number of times put was called:" + d.size());
   }
}

Output

Number of times put was called:3
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