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Add map data structure
Jan 12, 2025
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HashtableDataStructure.java
HashtableDataStructure.java
Jan 12, 2025
README.md
README.md
Jan 12, 2025

README.md

Hashtable in Java

Overview

The Hashtable class in Java is a part of the java.util package and implements the Map interface. It is similar to HashMap, but with two key differences: it is synchronized (making it thread-safe) and does not allow null keys or values. It stores data in key-value pairs and provides constant-time performance for basic operations, such as get() and put().

Characteristics of Hashtable

Feature Details
Package java.util
Allows Duplicates No (Allows duplicate values, but not keys)
Thread-Safe Yes
Allows null Values No (Does not allow null keys or values)
Initial Capacity 11 (default)
Load Factor 0.75 (default)

Key Features of Hashtable

  • Key-Value Pairs: Stores data in key-value pairs.
  • Thread-Safe: Ensures thread safety with synchronization, though it may be slower compared to other Map implementations.
  • Does Not Allow null Keys or Values: Unlike HashMap, Hashtable does not allow null keys or values.
  • Fast Lookup: Provides constant time complexity (O(1)) for get() and put() operations under ideal conditions.

How to Use Hashtable

Importing Hashtable

import java.util.Hashtable;

Creating a Hashtable

Hashtable<KeyType, ValueType> hashtable = new Hashtable<>();
  • Example: 
    Hashtable<String, String> hashtable = new Hashtable<>();
Hashtable<Integer, String> hashtableWithIntegers = new Hashtable<>();

Hashtable Specific Methods

The Hashtable class provides several methods beyond those in the Map interface. Here are some of the most commonly used:

Method Description Return Type Example
put(K key, V value) Associates the specified value with the specified key. V hashtable.put("Name", "Alice");
get(Object key) Returns the value associated with the specified key. V hashtable.get("Name");
remove(Object key) Removes the mapping for the specified key from the map. V hashtable.remove("Name");
containsKey(Object key) Checks if the map contains a mapping for the specified key. boolean hashtable.containsKey("Name");
containsValue(Object value) Checks if the map contains the specified value. boolean hashtable.containsValue("Alice");
size() Returns the number of key-value mappings in the map. int hashtable.size();
clear() Removes all mappings from the map. void hashtable.clear();
isEmpty() Checks if the map is empty. boolean hashtable.isEmpty();
keySet() Returns a set view of the keys contained in the map. Set hashtable.keySet();
values() Returns a collection view of the values contained in the map. Collection hashtable.values();
entrySet() Returns a set view of the mappings contained in the map. Set<Map.Entry<K, V>> hashtable.entrySet();
putAll(Map<? extends K, ? extends V> m) Copies all of the mappings from the specified map to the current map. void hashtable.putAll(anotherMap);
equals(Object o) Compares the specified object with this map for equality. boolean hashtable.equals(otherMap);

Example Code

import java.util.Hashtable;

public class HashtableDataStructure {
    public static void main(String[] args) {
        // Create a Hashtable
        Hashtable<String, String> hashtable = new Hashtable<>();

        // Add key-value pairs
        hashtable.put("Name", "Alice");
        hashtable.put("Age", "25");
        hashtable.put("City", "New York");

        // Access value by key
        System.out.println("Value for 'Name': " + hashtable.get("Name"));

        // Check size
        System.out.println("Size of the hashtable: " + hashtable.size());

        // Check if a key exists
        System.out.println("Contains key 'Age': " + hashtable.containsKey("Age"));

        // Remove a key-value pair
        hashtable.remove("City");
        System.out.println("Hashtable after removal: " + hashtable);

        // Iterate over key-value pairs
        System.out.println("Iterating over hashtable:");
        for (Map.Entry<String, String> entry : hashtable.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }

        // Clear the hashtable
        hashtable.clear();
        System.out.println("Is hashtable empty? " + hashtable.isEmpty());
    }
}

For more: HashtableDataStructure.java