Calculate Perimeter, Area and checks for square based on X and Y cordinates

Point.java

package SRectangle;
// CC-BY : Osanda Malith Jayathissa
public class Point {
	private int x, y;
	
	public Point(int x, int y) {
		this.x=(x);
		this.y=(y);
	}
	public int getX() {
		return x;
	}

	public void setX(int x) {
		this.x = x;
	}

	public int getY() {
		return y;
	}

	public void setY(int y) {
		this.y = y;
	}
}

Rectangle.java

package SRectangle;
// CC-BY : Osanda Malith Jayathissa
public class Rectangle {
	
	private Point tl;
	private Point tr;
	private Point bl;
	private Point br;
	
	public Rectangle(Point tl, Point tr, Point bl, Point br) {
		 if(   tl.getX() < 20.0  &&  tl.getY() < 20.0 
			&& tr.getY() < 20.0  &&  tr.getY() < 20.0 
			&& bl.getY() < 20.0  &&  bl.getY() < 20.0 
			&& br.getY() < 20.0  &&  br.getY() < 20.0) {
				this.tl = (tl);     
	            this.tr = (tr);     
	            this.bl = (bl);  	  
	            this.br = (br);
		} else  System.err.println("Value should be below 20.0");
		  
		  if( tl.getX() != bl.getX() ) System.err.println("error: Top left and bottom left must have same X values"); 
		  if( tr.getX() != br.getX() ) System.err.println("error: Top right and bottom right must have same X values");
	}

	public Point getTopLeft()     { return tl; }
	public Point getTopRight()    { return tr; }
	public Point getBottomLeft()  { return bl; }
	public Point getBottomRight() { return br; }

	public double getWidth() {
		  Point tr = getTopRight();
		  Point tl = getTopLeft();
		  return tr.getX() - tl.getX();
	  }
	
	public double getHeight (){
		  Point tr = getTopRight();
		  Point br = getBottomRight();
		  return tr.getY() - br.getY();
	  }
	
	public double getPerimeter() { return 2*(getHeight() + getWidth()); }
	public double getArea()      { return getHeight() * getWidth();	    }
	public boolean isSquare()    { return getHeight() == getWidth();    }
}

Tester.java

package SRectangle;
// CC-BY : Osanda Malith Jayathissa
public class Tester {
	public static void main(String[] args) {
		
		Point tr = new Point(1,3);  	Point tl = new Point (3,3);
		Point br = new Point (1,1);   	Point bl = new Point (3,1);
		
		Rectangle rect = new Rectangle (tr,tl,br,bl);
		
		System.out.println("Height: " + rect.getHeight());
		System.out.println("Width: " + rect.getWidth());
		System.out.println("Area: " + rect.getArea());
		System.out.println("Perimeter: " + rect.getPerimeter());
		System.out.println("Is square?: "+ rect.isSquare());
		
		tr = new Point(1,7);  	tl = new Point (3,7);
		br = new Point (1,1);   	bl = new Point(3,1);
		
		rect = new Rectangle (tr,tl,br,bl);
		
		System.out.println("\n\n");
		System.out.println("Height: " + rect.getHeight());
		System.out.println("Width: " + rect.getWidth());
		System.out.println("Area: " + rect.getArea());
		System.out.println("Perimeter: " + rect.getPerimeter());
		System.out.println("Is square?: "+ (rect.isSquare() ? "yes":"no"));
		
	}
}