On what principle does the number of buckets increase?

In Java, for example in the implementation of HashMap, the number of buckets (internal containers for storing elements) increases by doubling the current size. Initially, an array of buckets of a certain size is created (usually a power of two, for example 16). When the number of elements exceeds a certain threshold (load factor, usually 0.75), a resize occurs — a new array of buckets twice as large is created, and all existing elements are redistributed across the new buckets.

This doubling helps maintain the efficiency of insert and search operations, minimizing collisions and providing amortized access time.

Example:

// When the threshold is exceeded
if (size > threshold) {
    resize(); // bucket size is doubled
}

private void resize() {
    int newCapacity = oldCapacity * 2;
    // create a new array and redistribute elements
}