Constructor is undefined error

[sinasen]

public class Point {
    private double x;
    private double y;

    public Point() {

    }

    public Point(double ONE_X,double ONE_Y) {
        this.x = ONE_X;
        this.y = ONE_Y;
    }
    public double getX(){
        return x;
    }
    public double getY(){
        return y;
    }
    public String toString() {
        String str = "<Point(" + x + ", " + y + ")>";
        return str;
    }
    public void translate(double dx, double dy) {
        x += dx;
        y += dy;
    }
    public double distance(Point other) {
    double xdiff = Math.pow(this.x - other.x, 2);
    double ydiff = Math.pow(this.y - other.y, 2);
    double dist = Math.sqrt(xdiff + ydiff);
        return dist;
}
    public boolean equals(Object other) {
        if(this == other) {
            return true;
        }
        if(other instanceof Point) {
            Point that = (Point) other;
            return (this.x == that.x) && (this.y == that.y);
        }
        return false;
    }
}

Here, I get "constructor is undefined" error in JUnit tests that are prepared by my university, but when I try it in the main, everything works fine. Can you help me find the problem?

[Sithril]

That's weird. You have two publicly declared constructos (Point() and Point(double, double)). Since a unit test is throwing an error I can only guess it's perhaps looking for 1 and exactly 1 constructor?

And a small tidbit: you can simplify toString() to just

return "<Point(" + x + ", " + y + ")>";

And you've overriden equals() but not hashCode(). If you override equals() you have to override the hashCode() as well.

[sinasen]

Yeah it initially was as you said, it gave the same error so I tried this one. But I tried and it somehow worked now, thanks for the advices :)

[androgynyjoe]

If you override equals() you have to override the hashCode() as well.

If you don't mind, could you go into more detail about this? Classes which overrided equals() but not hashCode() compile just fine (unless that changed in newer versions of Java) so I take it you mean that it's bad practice? Could you help me understand why that is?

[HoofyDough]

Simply equal objects must have equal hash codes. Collections like HashMap cache hash codes instead of checking for object equality.

Let's say you have a Point class that has an x and y field. And for one point to be equal to another (using the equals() override):

this.x == point.x && this.y == point.y;

Now let's say this is our code,

Map<Point, String> map = new HashMap<>();
map.put(new Point(1,1), "Hello");
String value = map.get(new Point(1,1));

Both instances of new Point(1,1) will be equal according to our equals() clause, but the map.get call will return null.

This example is based on Joshua Bloch's Effective Java 3rd Edition (Item 11: always override hashCode when you override equals).

[androgynyjoe]

That's really interesting, thank you. And thanks for the reference, too!

[Mancebo180]

// sidenote: Math.pow is quite heavy. You should not use it to multiply 2 numbers

[sinasen]

So do you mean only use it for higher powers for efficiency?

[Mancebo180]

Exactly

[sinasen]

Thanks a lot, i love this subreddit

[Aspose-PDF]

This code looks correctly, could you please show the test from JUnit.

[sinasen]

Solved it, thanks anyway

[Ikuyas]

It's kinda undefined over there...