How does HashMap expand when it fills up?

In Java, HashMap expands when the number of elements exceeds a certain threshold, usually the load factor (default 0.75) multiplied by the current array size (capacity). When this threshold is reached, a new array with an increased size (usually double) is created, and all existing entries are redistributed (rehash) into the new array.

It roughly looks like this:

• Initially, capacity = 16
• Load factor = 0.75
• Maximum number of elements before expansion = 16 * 0.75 = 12
• When adding the 13th element, expansion occurs

This helps maintain the efficiency of insert and search operations by reducing the number of collisions.