Differences Between HashMap and Hashtable in Java

What are the differences between a HashMap and a Hashtable in Java?

// Example of HashMap usage
HashMap<String, Integer> hashMap = new HashMap<>();
hashMap.put("One", 1);
hashMap.put("Two", 2);

// Example of Hashtable usage
Hashtable<String, Integer> hashtable = new Hashtable<>();
hashtable.put("One", 1);
hashtable.put("Two", 2);

HashMap and Hashtable are two data structures in Java that implement the Map interface. Their primary role is to store key-value pairs but they differ significantly in synchronization, performance, and usage.

// HashMap example
HashMap<String, String> map = new HashMap<>();
map.put(null, "Null Key"); // Allowed

// Hashtable example
Hashtable<String, String> table = new Hashtable<>();
table.put(null, "Null Key"); // Throws NullPointerException

Causes

• HashMap is non-synchronized and allows null keys and values, making it more efficient for non-threaded applications.
• Hashtable is synchronized and does not allow null keys or values, making it suitable for threaded applications at the cost of performance.

Solutions

• Use HashMap for non-threaded applications to ensure better performance and flexibility with null values.
• Choose Hashtable only when thread safety is a necessary concern.

Mistake: Using Hashtable without need for synchronization.

Solution: Opt for HashMap for better performance if thread safety isn't required.

Mistake: Assuming HashMap is thread-safe.

Solution: Remember that HashMap is not synchronized. If you need a thread-safe option, consider using ConcurrentHashMap.