Java Hashtable Class

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Hashtable belongs to the Java Collections Framework and is defined within the java.util package. It is a key-value pair data structure like HashMap, but with one major difference: Hashtable is synchronized, meaning it is thread-safe.

Key Features

  • Stores key-value pairs
  • Thread-safe (synchronized)
  • The Hashtable data structure prevents the usage of both null keys and null values.
  • Slower than HashMap due to synchronization
  • Preserves no order

Syntax

Hashtable<KeyType, ValueType> table = new Hashtable<>();

Example

Hashtable<Integer, String> students = new Hashtable<>();

Example

 import java.util.Hashtable;
import java.util.Map;

public class HashtableExample {
    public static void main(String[] args) {
        Hashtable<Integer, String> employees = new Hashtable<>();

        // Adding key-value pairs
        employees.put(100, "Alice");
        employees.put(101, "Bob");
        employees.put(102, "Charlie");

        // Display all entries
        for (Map.Entry<Integer, String> entry : employees.entrySet()) {
            System.out.println("ID: " + entry.getKey() + ", Name: " + entry.getValue());
        }

        // Update and remove
        employees.put(101, "Bobby");
        employees.remove(100);

        // Check contains
        System.out.println("Has key 102? " + employees.containsKey(102));
        System.out.println("Has value 'Charlie'? " + employees.containsValue("Charlie"));

        // Size
        System.out.println("Size: " + employees.size());
    }
}
Run ›

Note

  • Hashtable should be employed exclusively for legacy systems where thread safety is essential.
  • For modern thread-safe applications, prefer ConcurrentHashMap.
  • Slower performance than HashMap due to synchronization.
  • The Java Collections Framework initially did not include this component which was incorporated afterward.
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