Dictionary Abstract Class in Map Interface

The Dictionary abstract class in the Map interface is a legacy class that serves as the superclass for specific types of data structures that map keys to values. It provides a basic implementation for key-value mapping functionality.

Key Features

• Abstract Class: The Dictionary class is an abstract class, which means it cannot be directly instantiated. It provides a base implementation for key-value mapping but requires concrete subclasses to define specific implementations.
• Key-Value Mapping: The Dictionary class allows you to map keys to values, similar to other implementations of the Map interface. However, it is considered a legacy class, and it is recommended to use the newer implementations such as HashMap or TreeMap instead.
• No Null Keys: The Dictionary class does not allow null keys. If a null key is passed, it will throw a NullPointerException.

Methods

The Dictionary class provides several methods for working with key-value pairs. Some of the important methods include:

abstract int size()
abstract boolean isEmpty()
abstract Enumeration<V> elements()
abstract Enumeration<K> keys()
abstract V get(Object key)
abstract V put(K key, V value)
abstract V remove(Object key)

Example

Here's an example of using the Dictionary class in Java:

import java.util.Dictionary;
import java.util.Hashtable;

public class DictionaryExample {
    public static void main(String[] args) {
        Dictionary>String, Integer< dictionary = new Hashtable>lt;();

        dictionary.put("one", 1);
        dictionary.put("two", 2);
        dictionary.put("three", 3);

        for (String key : dictionary.keys()) {
            System.out.println(key + " : " + dictionary.get(key) );
        }
        
    }
}

Output:

three : 3
two : 2
one : 1

In this example, we use the Hashtable class, which implements the Dictionary class. We create a Dictionary object with String keys and Integer values and add three key-value pairs to it.

We then iterate over the keys using the keys method and print each key-value pair the output as an unordered list .

Conclusion

The Dictionary abstract class in the Map interface provides a basic implementation for key-value mapping functionality. It is a legacy class and is recommended to use newer implementations such as HashMap or TreeMap for key-value mapping in Java applications.

I hope this explanation helps you understand the Dictionary abstract class in the Map interface in Java! Let me know if you have any further questions.

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