Java · Theory

Difference between HashMap and Hashtable

Theory

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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.

Diagram

put("Asha", 90)
  get("Asha") → 90
  get("Neha") → null

Exam tip

Explain bucket + equals for collisions in one line.

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.

Short notes

DefDifference between HashMap and Hashtable — List = order + duplicates OK. Set = unique. Map = key → value.
RuleDifference between HashMap and Hashtable — pick it only when that structure matches the problem.
RememberDifference between HashMap and Hashtable — generics List<String>. ArrayList for daily lists. HashMap for lookup.
TrapDifference between HashMap and Hashtable — using arrays for everything that must grow, or mixing List/Set/Map.

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

Example

Short notes

Questions

Difference between HashMap and Hashtable

Example

Short notes

Questions