How is resizing handled in a HashMap in Java?

In Java, the resizing operation of a HashMap is done automatically without the need for manual intervention. When the number of elements in the HashMap exceeds the product of the load factor and initial capacity, the HashMap will automatically resize.

The load factor is a floating point number between 0 and 1, representing the maximum number of elements allowed in a HashMap compared to its current capacity. By default, the load factor is 0.75.

During the resizing process, HashMap will create a new larger capacity array and rehash all elements into the new array. The specific steps of the resizing operation include the following:

1. Create a new array with a capacity that is twice the size of the original array.
2. Iterate through each element in the original array and calculate its position in the new array.
3. If multiple elements need to be placed in the same location, conflicts can be resolved using a linked list or a red-black tree (for JDK1.8 and later versions).
4. Place the elements in their respective positions on the new array.
5. Reference the original array to the new array and discard the original array.

During the expansion process, HashMap can still be used normally and will automatically migrate elements from the old array to the new array as needed. The time complexity of expansion is O(n), where n is the number of elements in the HashMap.

Adjusting the load factor and initial capacity of a HashMap can impact the frequency of resizing and performance. In general, a smaller load factor and larger initial capacity can decrease the frequency of resizing, improve performance, but may consume more memory space.