Projectile.java

public class Projectile {
  
    public double angleOfLaunch; // in radians
    public double initialX; // in meters
    public double initialVelocity; // in m/s

    public boolean useTimeToMaxHeight = false;

    private double gravity; // m/s^2

    public String description;


    public Projectile(String description, double angleOfLaunch, double initialVelocity, double initialX) {
        this(description, angleOfLaunch, initialVelocity, initialX, 9.81);
    }

    public Projectile(String description, double angleOfLaunch, double initialVelocity) {
        this(description, angleOfLaunch, initialVelocity, 0);
    }

    public Projectile(String description, double angleOfLaunch, double initialVelocity, boolean useTimeToMaxHeight) {
        this(description, angleOfLaunch, initialVelocity, 0);
        this.useTimeToMaxHeight = useTimeToMaxHeight;
    }

    public Projectile(String description, double angleOfLaunch, double initialVelocity, double initialX, double gravity) {
        this.angleOfLaunch = angleOfLaunch;
        this.initialX = initialX;
        this.initialVelocity = initialVelocity;
        this.description = description;
        this.gravity = gravity;
    }

    public void setGravity(double gravity) {
        this.gravity = gravity;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public double getTimeTaken() {
        if (useTimeToMaxHeight) {
            return getYComponent() / gravity;
        }
        return 2 * getYComponent() / gravity;
    }

    private double getYComponent() {
        return initialVelocity * Math.sin(angleOfLaunch);
    }

    private double getXComponent() {
        return initialVelocity * Math.cos(angleOfLaunch);
    }

    public double getMaxHeight() {
        return getYComponent() * getTimeTaken();
    }

    public double getRange() {
        return getXComponent() * getTimeTaken();
    }

    public static double degreesToRadians(int degrees) {
        return Math.PI / 180 * degrees;
    }
    public static double radiansToDegrees(double radians) {
        return radians * 180 / Math.PI;
    }

    public String toString() {
        return "Projectile[" + description + ": angle of launch " + round(radiansToDegrees(angleOfLaunch)) +" degrees, launch velocity " + initialVelocity + " m/s, range " + round(getRange()) + " m, max height "+ round(getMaxHeight()) + " m, time taken " + round(getTimeTaken()) + "s]";
    }

    private static double round(double d) {
        return Math.round(d * 100) / 100.0;
    }

    public static void main(String[] args) {
        // this doesn't take drag into account, so the earth one is a bit less: around 20 meters less
        Projectile p = new Projectile("Golf ball on the earth", Projectile.degreesToRadians(16), 59.28);
        System.out.println(p); // average golf shot
        p.setGravity(1.62);
        p.setDescription("Golf ball on the moon");
        System.out.println(p); // average golf shot with gravity of the moon

        // moon because it has no atmosphere, so the results will be more realistic
        System.out.println(new Projectile("Bullet fired on the moon", Projectile.degreesToRadians(10), 200, 0, 1.62));

        // a firework configured to explode at the top of its trajectory
        System.out.println(new Projectile("Firework", Projectile.degreesToRadians(75), 70, true));
    }
}