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    <p>I see no reason why that shouldn't work. Ok, there are a few problems here:</p> <ul> <li><code>positionList = new ArrayList&lt;&gt;();</code> will not compile. It must be <code>positionList = new ArrayList&lt;Position&gt;();</code></li> <li>As Jodaka said you would get every Position twice in the list when you get it the second time (three times when you call it the fourth and so on).</li> <li>Your implementation would include the first column and row but not the last (try <code>i &lt;= maxColumn</code> and <code>j &lt;= maxRow</code> in the loops).</li> </ul> <p>For my test I used Points instead of Position and added some casts for Points use ints as constructor argument but return double. But I didn't change the logic itself:</p> <pre><code>package spreadsheet; import java.awt.Point; import java.util.ArrayList; public class Range { private final Point a; private final Point b; private final ArrayList&lt;Point&gt; PointList; // Creates a new range, where it makes sure that the Points, // appear in the right order, where the first Point is the Point // of the upper left corner, and the second Point is the lower right corner. public Range(final Point a, final Point b) { int minColumn = (int) Math.min(a.getX(),b.getX()); int minRow = (int) Math.min(a.getY(),b.getY()); int maxColumn =(int) Math.max(a.getX(),b.getX()); int maxRow = (int) Math.max(a.getY(),b.getY()); this.a = new Point(minColumn, minRow); this.b = new Point(maxColumn, maxRow); PointList = new ArrayList&lt;Point&gt;(); } public ArrayList&lt;Point&gt; getPoints() { int minColumn = (int) a.getX(); int minRow = (int) a.getY(); int maxColumn = (int) b.getX(); int maxRow = (int) b.getY(); for (int i = minColumn; i &lt; maxColumn; i++) { for (int j = minRow; j &lt; maxRow; j++) { PointList.add(new Point(i, j)); } } return PointList; } </code></pre> <p>The Test:</p> <pre><code>package spreadsheet; import java.awt.Point; import java.util.ArrayList; import org.junit.Test; public class RangeTest { @Test public void testSomePoints() throws Exception { Range range = new Range(new Point(1, 1), new Point(5, 5)); ArrayList&lt;Point&gt; points = range.getPoints(); for (Point point : points) { System.out.println(point); } } } </code></pre> <p>The result:</p> <pre><code>java.awt.Point[x=1,y=1] java.awt.Point[x=1,y=2] java.awt.Point[x=1,y=3] java.awt.Point[x=1,y=4] java.awt.Point[x=2,y=1] java.awt.Point[x=2,y=2] java.awt.Point[x=2,y=3] java.awt.Point[x=2,y=4] java.awt.Point[x=3,y=1] java.awt.Point[x=3,y=2] java.awt.Point[x=3,y=3] java.awt.Point[x=3,y=4] java.awt.Point[x=4,y=1] java.awt.Point[x=4,y=2] java.awt.Point[x=4,y=3] java.awt.Point[x=4,y=4] </code></pre> <p><em>edit:</em></p> <p>I would see every point twice too, if I would call getPoints() a second time. You create the list once but add points every time you call getPoints().</p> <p>There are several possibilities:</p> <ol> <li>You could create the ArrayList in the getPoints() method and not in the constructor. But normally you wouldn't want to create an entirely new list each time you call this method...</li> <li>You could store the list in a field, calculate it in the constructor and use only a getter that returns the field.</li> <li>Similar to the second possibility, but you could calculate the list on demand. So don't calculate it in the constructor but in the getter <strong>if it is null by now</strong> and use the stored list otherwise.</li> </ol> <p><em>2. edit</em></p> <ol> <li><p>option:</p> <pre><code>public class Range { private final Point a; private final Point b; private final ArrayList&lt;Point&gt; PointList; public Range(final Point a, final Point b) { int minColumn = (int) Math.min(a.getX(),b.getX()); int minRow = (int) Math.min(a.getY(),b.getY()); int maxColumn =(int) Math.max(a.getX(),b.getX()); int maxRow = (int) Math.max(a.getY(),b.getY()); this.a = new Point(minColumn, minRow); this.b = new Point(maxColumn, maxRow); } public ArrayList&lt;Point&gt; getPoints() { PointList = new ArrayList&lt;Point&gt;(); int minColumn = (int) a.getX(); int minRow = (int) a.getY(); int maxColumn = (int) b.getX(); int maxRow = (int) b.getY(); for (int i = minColumn; i &lt; maxColumn; i++) { for (int j = minRow; j &lt; maxRow; j++) { PointList.add(new Point(i, j)); } } return PointList; } } </code></pre></li> <li><p>option:</p> <pre><code>public class Range { private final Point a; private final Point b; private final ArrayList&lt;Point&gt; PointList; public Range(final Point a, final Point b) { int minColumn = (int) Math.min(a.getX(),b.getX()); int minRow = (int) Math.min(a.getY(),b.getY()); int maxColumn =(int) Math.max(a.getX(),b.getX()); int maxRow = (int) Math.max(a.getY(),b.getY()); this.a = new Point(minColumn, minRow); this.b = new Point(maxColumn, maxRow); PointList = calcPoints(); } private ArrayList&lt;Point&gt; calcPoints() { ArrayList&lt;Point&gt; list = new ArrayList&lt;Point&gt;(); int minColumn = (int) a.getX(); int minRow = (int) a.getY(); int maxColumn = (int) b.getX(); int maxRow = (int) b.getY(); for (int i = minColumn; i &lt; maxColumn; i++) { for (int j = minRow; j &lt; maxRow; j++) { PointList.add(new Point(i, j)); } } return list; } public ArrayList&lt;Point&gt; getPoints() { return PointList; } } </code></pre></li> <li><p>option:</p> <pre><code>public class Range { private final Point a; private final Point b; private final ArrayList&lt;Point&gt; PointList; public Range(final Point a, final Point b) { int minColumn = (int) Math.min(a.getX(),b.getX()); int minRow = (int) Math.min(a.getY(),b.getY()); int maxColumn =(int) Math.max(a.getX(),b.getX()); int maxRow = (int) Math.max(a.getY(),b.getY()); this.a = new Point(minColumn, minRow); this.b = new Point(maxColumn, maxRow); } private ArrayList&lt;Point&gt; calcPoints() { ArrayList&lt;Point&gt; list = new ArrayList&lt;Point&gt;(); int minColumn = (int) a.getX(); int minRow = (int) a.getY(); int maxColumn = (int) b.getX(); int maxRow = (int) b.getY(); for (int i = minColumn; i &lt; maxColumn; i++) { for (int j = minRow; j &lt; maxRow; j++) { list.add(new Point(i, j)); } } return list; } public ArrayList&lt;Point&gt; getPoints() { if(PointList == null) { PointList = calcPoints(); } return PointList; } } </code></pre></li> </ol>
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    1. POWhat is wrong with this implementation of Range class
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    1. COThanks a lot for the help! :) I do however not understand why I would get every Position twice. So what should I correct in order to avoid that? And you do not seem to get each point twice, even though your code only differs from mine in that you have replaced Point with Position...
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    2. COHave a look at my edit :)
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    3. COAh yeah ok I think, I can see the problem now! So the second option would mean that everytime I created a range, I would also create an ArrayList with all those positions contained in that range? And the third one, I would have a getter method, where I could only create it if my field was null? And that field would that be of the type ArrayList<Position>? And thanks a lot for helping me, most appreciated! :)
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