View source for PowersOf2Iterable

=Motivation=
* Gain experience with implementing interfaces.
* Build a utility which will come in handy later in the semester (for example, the [[Scan]] exercise).

<!--
=Warm Ups=
If you are struggling with this studio, consider completing one or both of the warm ups
==Shape==
Complete the [[Shape]] warm up to gain experience with implementing an interface, as well as declaring and using fields.

==DoubleRange==
The [[DoubleRange]] warm up to gain experience implementing an Iterable<T> without simply containing a List<T> which holds the values.  Further, you can gain experience creating instances of an anonymous class.

<youtube>Dww-_5EiwA8</youtube>
-->

=Investigate=
[https://docs.oracle.com/javase/tutorial/java/javaOO/anonymousclasses.html anonymous classes]

interface [https://docs.oracle.com/javase/8/docs/api/java/lang/Iterable.html Iterable<T>]

interface [https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html Iterator<T>]

{{CollapsibleYouTube|Implementing Iterable and Iterator|<youtube>4ycpqdJ4yb4</youtube>}}

=Mistakes To Avoid=
{{warning | Do NOT Parallelize}}

{{warning | Do NOT confuse [https://docs.oracle.com/javase/8/docs/api/java/lang/Iterable.html Iterable<T>] from [https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html Iterator<T>]}}

=Client=
{{Client|PowersOfTwoLessThanClient|iteration.powersoftwo.client|main}}

{{CollapsibleCode|PowersOfTwoLessThanClient|
<syntaxhighlight lang="java">
for (int powerOf2 : new PowersOfTwoLessThan(231)) {
	System.out.println(powerOf2);
}
</syntaxhighlight>}}

{{CollapsibleConsole|PowersOfTwoLessThanClient Output|<pre style="border: 0px; background: #000; color:#fff;">1
2
4
8
16
32
64
128</pre>}}

=Code to Implement=
It is important to consider what state each class should encapsulate.  The class PowersOfTwoLessThan, which is Iterable, should be have need to store little (if anything) beyond the maxExclusive passed in to its constructor.  Further, PowersOfTwoLessThan should be immutable.  There is no need to change any of the data during its lifetime.

The Iterator<Integer> instances created whenever one invokes the iterator() method?  Now, the data for those instances are going to need to mutate.

One should NOT need to create a List to support this class.  A single private final int instance variable is all you need for PowersOfTwoLessThan and a single (mutable) int instance variable is all you need for its Iterator.

{{CodeToImplement|PowersOfTwoLessThan|constructor<br/>iterator|iteration.powersoftwo.exercise}}

==constructor==
{{SequentialConstructor|public PowersOfTwoLessThan(int maxExclusive)}}

==iterator==
{{Sequential|public Iterator<Integer> iterator()}}

You can create an [https://docs.oracle.com/javase/tutorial/java/javaOO/anonymousclasses.html anonymous inner class] or a named class if you prefer.

Note: if you type the following, and hover over the red line, IntelliJ will offer you to "Implement methods" necessary to create an anonymous inner class. You only need to override the '''hasNext()''' and '''next()''' methods.

<syntaxhighlight lang="java">
return new Iterator<>() {
      // Implement/Override necessary methods
};
</syntaxhighlight>

=Testing Your Solution=
==Correctness==
{{TestSuite|_PowersOfTwoTestSuite|iteration.powersoftwo.exercise}}

=Pledge, Acknowledgments, Citations=
{{Pledge|studio-powers-of-two-iterable}}