Lesson 9 - The Collections Java utility class - Creating collections
In the previous lesson, The Collections Java utility class - Getting and modifying, we learned how to use the
Collections Java utility class for getting and modifying collection
data. In today's Java tutorial, we're going to complete this survey by
introducing the functionality for creating new collections.
Creating new collections
The class has plenty of methods for creating empty collections of various
types. Usually it's about implementing a certain interface, but with zero number
of elements. Maybe you ask, what are these methods for? Such methods are useful,
for example, when we need to return a collection of elements matching some
condition. If no item satisfies the condition, we simply return an empty
collection, for example, using the
It's much better than returning
null, and clearer than returning
empty*() methods return an
unmodifiable collection. This means that you're not able to add,
remove, or get any element from that collection.
Methods that belong to this category create wrappers over existing collections. The wrappers are of three types:
- synchronization wrappers
- unmodifiable wrappers
- typesafe wrappers
Synchronization wrappers are used to
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