HashMap Internal Working in Java

Vinotech

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Jul 19, 2026

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HashMap Internal Working in Java

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A HashMap stores data as Key → Value pairs

Example:

HashMap<Integer, String> map = new HashMap<>();

map.put(101, "Vinoth");
map.put(102, "Kumar");
map.put(103, "Raj");

Internally:

101  -> Vinoth
102  -> Kumar
103  -> Raj

Step 1: Create a HashMap

HashMap<Integer, String> map = new HashMap<>();

Internally, Java creates a bucket array.

Initially:

HashMap

Bucket Array

HashMap<Integer, String> map = new HashMap<>();

Default Capacity = 16 buckets
Load Factor = 0.75

                 Table (Bucket Array)
      +---------------------------------------+
Index |              Bucket                   |
------+---------------------------------------+
  0   |   -
------+---------------------------------------+
  1   |   -
------+---------------------------------------+
  2   |   -
------+---------------------------------------+
  3   |   -
------+---------------------------------------+
  4   |   -
------+---------------------------------------+
  5   |  -
------+---------------------------------------+
  6   |   -
------+---------------------------------------+
  7   |   -
------+---------------------------------------+…