I am getting the error message "cannot convert from void to boolean" when I try to run this conditional in draw():

RectSelectionTool selectRectangle;
EllipseSelectionTool selectEllipse;


void setup() {
  size (screen.width, screen.height);
  background (225, 225, 255);
  selectRectangle = new RectSelectionTool (0, 0, 0, 0, 0, 0, 50, 50);
  selectEllipse=new EllipseSelectionTool (0, 0, 0, 0, 0, 50, 50, 50);
}

void draw() {
  background (225, 225, 255);

  if (selectRectangle.rollOver(true)) {
    selectRectangle.select();
    selectRectangle.display();
  }
  else {  // do nothing
  }

  if (selectEllipse.rollOver(true)) {
    selectEllipse.select();
    selectEllipse.display();
  }
  else {  // do nothing
  }
}


// mouse and keyboard events

void mousePressed () {
  selectRectangle.click (mouseX, mouseY);
  selectEllipse.click (mouseX, mouseY);
}

void mouseDragged() {
}

void mouseReleased () {
  selectRectangle.release ();
  selectEllipse.release();
}

void keyPressed () {
}



abstract class InteractiveBoxes {

  int boxPosX, boxPosY, boxPosW, boxPosH;
  int boxPosXOff, boxPosYOff;
  boolean over = false;
  boolean pressed = false;

  InteractiveBoxes (int tempBoxPosX, int tempBoxPosY, int tempBoxWidth, int tempBoxHeight) {

    boxPosX=tempBoxPosX;
    boxPosY=tempBoxPosY;
    boxPosW=tempBoxWidth;
    boxPosH=tempBoxHeight;
  }

  // methods of the abstract InteractiveBoxes class

  void rollOver () {
    if ((mouseX>=boxPosX) && (mouseX <=boxPosX+boxPosW) && (mouseY>=boxPosY) && (mouseY<=boxPosY+boxPosH)) {
      over=true;
    }
    else {
      over=false;
    }
  } // end of the rollOver function


  void click (int mX, int mY) {
    boxPosX=mouseX;
    boxPosY=mouseY;
    boxPosW=mouseX-boxPosX;
    boxPosH=mouseY-boxPosY;
  } // end the click function


  void press (int mX, int mY) {
    if (over==true) {
      pressed=true;
      boxPosXOff=mX-boxPosX;
      boxPosYOff=mY-boxPosY;
    }
  }  // end of the press function


  void drag (int mX, int mY) {
    if (pressed==true) {
      boxPosX=mX-boxPosXOff;
      boxPosY=mY-boxPosYOff;
    }
  }  // end of the drag function


  void release () {
    pressed=false;
  }  // end of release function
}


abstract class  SelectionTool extends InteractiveBoxes {

  PImage icon;
  int iconXPos, iconYPos, iconW, iconH;
  int SelectX, SelectY, SelectW, SelectH;
  boolean activate = false;

  // constructor of the abstract SelectionTool class

  SelectionTool (int boxPosX, int boxPosY, int boxPosW, int boxPosH, int tempIconXPos, int tempIconYPos, int tempIconW, int tempIconH) {
    super (boxPosX, boxPosY, boxPosW, boxPosH);

    iconXPos=tempIconXPos;
    iconYPos=tempIconYPos;
    iconW=tempIconW;
    iconH=tempIconH;
  }  // end of the constructor


  // methods of the abstract SelectionTool class


  void rollOver (boolean over) {
    if (mousePressed && (mouseX>=iconXPos) && (mouseX <=iconXPos+iconW) && (mouseY>=iconYPos) && (mouseY<=iconYPos+iconH))
    {
      over=true;
    }
    else {
      over=false;
    }
  } // end of the rollOver function



  void release () {
    pressed=false;
    SelectX=boxPosX;
    SelectY=boxPosY;
    SelectW=mouseX-boxPosX;
    SelectH=mouseY-boxPosY;
  }  // end of release function



  abstract void select ();

  void display () {
    image (icon, iconXPos, iconYPos);
  }  // end of the display function
}  // end of the  SelectionTool class



class  RectSelectionTool extends SelectionTool {



  // constructor of the  RectSelectionTool class

  RectSelectionTool (int boxPosX, int boxPosY, int boxPosW, int boxPosH, int iconXPos, int iconYPos, int iconW, int iconH) {
    super (boxPosX, boxPosY, boxPosW, boxPosH, iconXPos, iconYPos, iconW, iconH);

    icon=loadImage("rectangularmarquee.jpg");
  }  // end of the constructor

  // methods of the RectSelectionTool class


  void select () {
    strokeWeight(1);
    stroke(0, 0, 255);
    fill (0, 0, 0, 0);
    ellipseMode(CORNER);
    if (mousePressed)
    {
      rect (boxPosX, boxPosY, mouseX-boxPosX, mouseY-boxPosY);
    }
    else {
      rect (SelectX, SelectY, SelectW, SelectH);
    }
    stroke(0);
  }
}  // end of the  RectSelectionTool class



class  EllipseSelectionTool extends SelectionTool {

  // constructor of the  EllipseSelectionTool class

  EllipseSelectionTool (int boxPosX, int boxPosY, int boxPosW, int boxPosH, int iconXPos, int iconYPos, int iconW, int iconH) {
    super (boxPosX, boxPosY, boxPosW, boxPosH, iconXPos, iconYPos, iconW, iconH);

    icon=loadImage ("ellipticalmarquee.jpg");
  }  // end of the constructor


  // methods of the EllipseSelectionTool class


  void select () {
    strokeWeight(1);
    stroke(0, 0, 255);
    fill (0, 0, 0, 0);
    if (mousePressed) {
      ellipseMode(CORNER);
      ellipse (boxPosX, boxPosY, mouseX-boxPosX, mouseY-boxPosY);
    }
    else {
      ellipseMode(CORNER);
      ellipse (SelectX, SelectY, SelectW, SelectH);
    }
    stroke(0);
  }
}  // end of the  EllipseSelectionTool class