What is the usage of the Java iterator?

The Java Iterator is an interface used to traverse collection objects, providing a uniform way to access elements in the collection without exposing the internal structure of the collection.

Iterators can be used to access each element in a collection sequentially without knowing the internal implementation of the collection. They provide basic methods for traversing collections, including determining if there is another element, getting the next element, and deleting the current element.

The main uses of iterators are as follows:

1. Create an iterator: Obtain an iterator instance by calling the iterator() method of the collection object. For example, Iterator iterator = list.iterator();
2. Iterate through a collection: Use the hasNext() method of the iterator to check if there is another element, and if so, use the next() method to retrieve it. For example, while (iterator.hasNext()) { String element = iterator.next(); }
3. Remove element: By using the remove() method of the iterator, you can delete the current element in the collection. For example, iterator.remove(); can safely delete the element returned by the last call to the next() method.

It is important to note that once you are using an iterator to traverse a collection, you cannot directly modify the collection, otherwise a ConcurrentModificationException will be thrown. If you need to modify the collection, you should use the remove() method of the iterator to delete elements.

Iterators are a commonly used way to traverse collections, suitable for different types of collections such as List, Set, and Queue. They simplify the process of traversing collections and provide a uniform method of iteration.