# Java Collectors

[CG]jupoulton
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## What's a Collector?

A Collector is a Java construct to use in conjunction with streams in order to turn a stream into a whatever-you-like.

Built-in Collectors exist and include:

• toList() Everything ends up in a list
• toSet() Everything ends up in a set
• joining(String s) Everything ends up in a string, separated by s
• And many more along the same lines.

Where are they ? in java.util.stream.Collectors;.

## Using a built-in Collector

There are many reasons why you might want to write your own Collector. Improving the readibility of a core part of your code is one of them.

Let's take a look at how to do this with an example.

Let's say you need to convert a string of space-separated integers to a list of Point instances where every two integers are X and Y coordinates.

There are a few methods to @Override when writing a new subclass of Collector. Look for every occurence of Fix me! to solve this exercice.