title: How to write a recursive function using static variables
body: <p>I am trying to write a code to get the set of points (x,y) that are accessible to a monkey starting from (0,0) such that each point satisfies |x| + |y| &lt; _limitSum. I have written the below code and have used static HashSet of members of Coordinate type (not shown here) and have written a recursive method AccessPositiveQuadrantCoordinates. But the problem is the members of the HashSet passed across the recursive calls is not reflecting the Coordinate members added in previous calls. Can anybody help me on how to pass Object references to make this possible? Is there some other way that this problem can be solved? </p>
  
  <pre><code>public class MonkeyCoordinates {
  public static HashSet&lt;Coordinate&gt; _accessibleCoordinates = null;
  private int _limitSum;
  public MonkeyCoordinates(int limitSum) {
      _limitSum = limitSum;
      if (_accessibleCoordinates == null)
          _accessibleCoordinates = new HashSet&lt;Coordinate&gt;();
  }
  public int GetAccessibleCoordinateCount() {
      _accessibleCoordinates.clear();
      Coordinate start = new Coordinate(0,0);
      AccessPositiveQuadrantCoordinates(start);
      return (_accessibleCoordinates.size() * 4);
  }
  private void AccessPositiveQuadrantCoordinates(Coordinate current) {
      if (current.getCoordinateSum() &gt; _limitSum) { return; }
      System.out.println("debug: The set _accessibleCoordinates is ");
      for (Coordinate c : _accessibleCoordinates) {
          System.out.println("debug:" + c.getXValue() + " " + c.getYValue());
      }
  
      if (!_accessibleCoordinates.contains(current)) { _accessibleCoordinates.add(current); }
      AccessPositiveQuadrantCoordinates(current.Move(Coordinate.Direction.East));
      AccessPositiveQuadrantCoordinates(current.Move(Coordinate.Direction.North));
  }
  </code></pre>
  
  <p>I will give points to all acceptable answers.</p>
  
  <p>Thanks ahead,
  Somnath</p>