Y axis inverted in code that should form a rectangle

Question

So i code consist of 3 parts 2 classes and test Idea is that 2 classes form a rectangle using inputs form the test. This is code for test

@Test
    public void testRectangle1() {
        Point center = new Point(20, 30);
        Rectangle rect = new Rectangle(center, 20, 20);
        assertAll(
                () -> assertEquals(10, rect.getTopLeft().getX()),
                () -> assertEquals(20, rect.getTopLeft().getY()),
                () -> assertEquals(30, rect.getBottomRight().getX()),
                () -> assertEquals(40, rect.getBottomRight().getY()),
                () -> assertEquals(20, rect.getWidth()),
                () -> assertEquals(20, rect.getHeight())
        );
    }

First class called Point it works fine.

public class Point {

    private int x, y;

    public Point(int x, int y) {
        this.x = x;
        this.y = y;
    }

    public Point() {
        this(0, 0);
    }

    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;
    }

    public void moveTo(int newX, int newY) {
        x = newX;
        y = newY;
    }

    public void moveRel(int dx, int dy) {
        x += dx;
        y += dy;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + x;
        result = prime * result + y;
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        Point other = (Point) obj;
        if (x != other.x)
            return false;
        if (y != other.y)
            return false;
        return true;
    }
}

So this is teh second class that forms recatangle itself. It consist of constructor on a few aditional methods for forming my rectangle

public class Rectangle {
    public int width = 0;
    public int height = 0;
    public Point center;

    public Rectangle(Point center, int width, int height) {
        int x = 0;
        int y = 0;
        this.width=width;
        this.height=height;
        this.center=center;
    }

    public Point getTopLeft() {
        Point point = new Point(center.getX(), center.getY());
        point.moveRel(- width / 2, height / 2);
        return point;
    }

    public Point getBottomRight() {
        Point point = new Point(center.getX(), center.getY());
        point.moveRel(width / 2, - height / 2);
        return point;
    }

    public int getWidth() {

        return width;
    }


    public int getHeight() {

        return height;
    }
}

So the problem is it seems that y axis is somehow inverted becouse when i run the test it returns wrong value, () -> assertEquals(20, rect.getTopLeft().getY()), Where it returns 40 instead of 20 and test () -> assertEquals(40, rect.getBottomRight().getY()), returns 2o instead of 40. So it seems that top left and bottom right point is inverted on y axis.

Answer 1

You add height/2 in moveRel to get topLeft. Hence it is normal that you get 40 and not 20.

Seems there is a sign error before height parameters in:

public Point getTopLeft() {
    Point point = new Point(center.getX(), center.getY());
    point.moveRel(- width / 2, height / 2);
    return point;
}

public Point getBottomRight() {
    Point point = new Point(center.getX(), center.getY());
    point.moveRel(width / 2, - height / 2);
    return point;
}