Dictionary Class in Java

In Java, Dictionary is the list of key-value pairs. We can store, retrieve, remove, get, and put values in the dictionary by using the Java Dictionary class. In this section, we will discuss the Java Dictionary class that stores data in key-value pairs just like the Map interface.

Java Dictionary Class

Java Dictionary class is an abstract class parent class of any class. It belongs to java.util package. Its direct known subclass is the Hashtable class. Like the Hashtable class, it also maps the keys to values. Note that every key and value is an object and any non-null object can be used as a key and as a value. The Dictionary class hierarchy is as follows:

Every key is associated with at most one value, as shown in the following figure. Once the value is stored in a dictionary object, we can retrieve it by using the key.

Syntax:

Note: The class is obsolete. So, implement the map interface instead of extending the class.

Dictionary Class Constructor

The class has only a constructor called a sole constructor.

Syntax:

Dictionary Class Methods

All the methods of the Dictionary class are abstract. The following table describes the methods.

Java Dictionary Programs

Use of Dictionary.put() Method

The put() method inserts the elements in the dictionary. The following program demonstrates the same.

InsertElementExample.java

Output:

{108=Canberra, 107=Nelson Bay, 106=Mount Gambier, 105=Lismore, 104=Perth, 103=Melbourne, 102=Brisbane, 101=Sydney}

Use of Dictionary.size() Method

The size of the dictionary is the number of elements the dictionary contains. In the following program, the size of the dictionary is 6.

DictionarySizeExample.java

Output:

The size of the dictionary is: 6

Use of Dictionary.get() Method

By using the get() method, we can retrieve the value of a specified key.

DictionaryGetElement.java

Output:

The value of the specified key is: Melbourne

Use of Dictionary.isEmpty() Method

It returns true if dictionary is empty, else returns false.

EmptyCheckExample.java

Output:

Is the dictionary empty? 
false

Use of Dictionary.remove() Method

The method removes the key and corresponding value that we have parsed in the method. The removed value is returned by the method.

RemoveElementExample.java

Output:

The removed value is: Mount Gambier

Use of elements() and key() Methods

RemoveElementExample.java

Output:

Dictionary values are: 

Canberra
Nelson Bay
Mount Gambier
Lismore
Perth
Melbourne
Brisbane
Sydney

Dictionary keys are: 

108
107
106
105
104
103
102
101

Difference Between the HashMap and Dictionary Class

The Java HashMap class and the Dictionary class both perform a similar function. The only difference is that HashMap implements the Map Interface while the Dictionary class does not. According to Java documentation, the Dictionary class is no longer in use because it is outdated. Instead of the Dictionary class, the HashMap class is used. Since we can say that HashMap is a type of dictionary.