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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 Collections.emptyList() method. It's much better than returning null, and clearer than returning Optional<List<T>>.

All the empty*() methods return an unmodifiable collection. This means that you're not able to add, remove, or get any element from that collection.

Wrappers

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

Synchronization wrappers are used to


 

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Article description

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In this Java tutorial, we'll discuss the Collections utility class in detail, this time the synchronization, unmodifiable and typesafe wrappers.

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Article has been written for you by Petr Štechmüller
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