Difference between HashMap and Hashtable — Java Technical Interview Questions & Answers

Difference between HashMap and Hashtable

Difference between HashMap and Hashtable

  • Difference between HashMap and Hashtable belongs to the Collections story. List = ordered, duplicates OK (ArrayList). Set = unique (HashSet). Map = key → value (HashMap). Pick by need, not by what you revised last.
  • For Difference between HashMap and Hashtable: ArrayList is the daily List: get(i) is fast, add at end is fast. HashMap lookup by key is average O(1). HashSet is unique values, no duplicates.
  • Use Difference between HashMap and Hashtable with generics: List<String>, Map<String, Integer>. Iterate with for-each or iterator. Don’t use a raw array when the size must grow.
  • Let's take this on the board with one tiny Main class — no extra files. Difference between HashMap and Hashtable — output: 90. HashMap stores Asha→90, Ravi→85. get("Asha") looks up the key. Start from main, go line by line, and stop at each print. That output is the proof for Difference between HashMap and Hashtable.
  put("Asha", 90)
  get("Asha") → 90
  get("Neha") → null

Technical Interview Tip: Explain bucket + equals for collisions in one line.

Code Examples for Difference between HashMap and Hashtable

Example

import java.util.HashMap;

// HashMap demo
public class Main {
  public static void main(String[] args) {
    HashMap<String, Integer> marks = new HashMap<>();
    marks.put("Asha", 90);
    marks.put("Ravi", 85);
    System.out.println(marks.get("Asha"));
  }
}

Difference between HashMap and Hashtable — output: 90. HashMap stores Asha→90, Ravi→85. get("Asha") looks up the key.

How to Explain Difference between HashMap and Hashtable to an Interviewer

What is the difference in Difference between HashMap and Hashtable?

Difference between HashMap and Hashtable — List = order + duplicates OK. Set = unique. Map = key → value. Difference between HashMap and Hashtable — pick it only when that structure matches the problem. Difference between HashMap and Hashtable — generics List<String>. ArrayList for daily lists. HashMap for lookup.

When do you pick each side?

Match the problem Don’t pick only what you revised last

Give one example of Difference between HashMap and Hashtable.

Show both sides Say the output

What mistake do beginners make?

Mixing both ideas Only memorising names

Where is Difference between HashMap and Hashtable used?

Real Java program