How is capacity used in Java?

In Java, capacity is typically used to specify the initial size of a collection class (such as ArrayList, HashMap, etc.). Capacity refers to the maximum number of elements that a collection can hold, not the actual number of elements currently contained in the collection.

Improving the performance of a collection object can be achieved by specifying the initial capacity when creating it. By using the capacity parameter to initialize the collection with an estimated number of elements it will contain, the number of times the collection internally reallocates space can be reduced, thus enhancing the efficiency of inserting and searching for elements.

For example, when creating an ArrayList, you can use a constructor with a specified capacity.

ArrayList<String> list = new ArrayList<>(10);

In this way, ArrayList will allocate space to hold 10 elements in advance, and will automatically resize as needed when the number of elements exceeds 10.

It is important to note that the capacity does not limit the actual number of elements stored in a collection, but rather pre-allocates a certain amount of space to improve performance. If the number of elements in the collection exceeds the capacity, the collection will automatically resize to accommodate more elements.