Methods Provided by Java — Data That Travels Together

Student: I was thinking through writing a method for a distance between points. I realized I needed to take a square root. There’s no operator that we’ve seen for that, right?

Prof: Right. Only the basic arithmetic operators, plus the comparisons like <, are operators. Java provides a number of built-in methods for things like this. For square root specifically, we can use a method defined on the built-in Math:

double sqrt(double n)

So you use it like:

double two = Math.sqrt(4.0);

Student: Oh, good. Now I can write my distance method.

Prof: What do you have so far?

Student: Here’s where I got to:

record Point(double x, double y) {
    double distanceTo(Point other) {
        double xdiff = other.x - x;
        double ydiff = other.y - y;
        return xdiff * xdiff + ydiff * ydiff;
    }
}
Point p = new Point(3.0, 4.0);
Point o = new Point(0.0, 0.0);
double dist = p.distanceTo(o); // should be 5.0, currently 25.0

Student: So I guess now I can add the square root:

record Point(double x, double y) {
    double distanceTo(Point other) {
        double xdiff = other.x - x;
        double ydiff = other.y - y;
        return Math.sqrt(xdiff * xdiff + ydiff * ydiff);
    }
}
Point p = new Point(3.0, 4.0);
Point o = new Point(0.0, 0.0);
double dist = p.distanceTo(o); // now correctly 5.0

Prof: Cool! There are a lot of other useful methods in the Math library. For example, you could use Math.pow(xdiff, 2) instead of

xdiff *
xdiff

, though either one is fine. There are also all the usual trig functions like sin and cos. Have a look there (or ask an AI agent about the Math library in Java) if you need to know about a specific one.

Practice

Math measures angles in radians. Finish Point so that angle() is the angle from the positive x axis, turning counterclockwise, up to the point, and degrees() is the same angle in degrees. For the point (1, 1) that is π/4 radians, or 45 degrees.

record Point(double x, double y) {
double angle() {
return Math.(y, x);
}
double degrees() {
return Math.(angle());
}
}
Point p = new Point(1.0, 1.0);
double angle = p.angle();
double degrees = p.degrees();