// Constructor
 public VisualWallParts(VisualMiddleSingle m)
 {
     this.upper        = null;
     this.lower        = null;
     this.middledouble = null;
     this.middlesingle = m;
 }
 // Constructor
 public VisualWallParts(VisualUpper u, VisualLower l, VisualMiddleDouble m)
 {
     this.upper        = u;
     this.lower        = l;
     this.middledouble = m;
     this.middlesingle = null;
 }