I am coding a method that calculates the intersection of a line and a circle as a first step to write some kind of ray casting demo. In case an intersection is calculated it gets the shortest distance to the two points of intersection that will be the collision point, then it repeats the process where the new line originates from the collision point.
I was motivated by this video of a laser hitting different circles.
The method receives the angle of the line, the point where it originates, the size of the window, the radius of the circles, the array of centers of the circles and the GraphicsContext object from JavaFX.
The method has a couple of booleans to determine whether a collision has been made or not, and an ArrayList to store the collisions that will be later drawn on a JavaFX Canvas.
Inside a while loop the equation of the line is defined with the form y = m*x + b. Then checks which of the circles has a distance between the circle center and the line smaller than the radius of the line, this is calculated with the method explained here: math.stackexchange.com.
In case the distance to the center is smaller than the radius a collision occurs against that circle. As far as I know to find the intersection between a line and a circle you need to solve the equation system: y = m*x + b, (x-x1)^2 + (y-y1)^2 = r^2, that I solved via substitution. This results in a second degree polinomial equation that has a real solution if: p1*p1 >= 4*p0*p2.
The solution with the shortest distance to the origin point is the one that the line hits first and is the solution to our problem. A new angle is calculated with the center of the circle, the collision point and the origin point. With this a new line is defined and the loop repeats until no collision against the circles is calculated, situation where the collision against the borders of the window is calculated.
At the end a for loop draws all of the lines defined as couples of points inside collisionList.
This is the code, I've tried to comment it as best as I could:
private void extendPoint(double angle, Point origin, double x, double y, double radius, ArrayList<Point> pointList) {
double newAngle = angle; //Angle that defines the direction of the line
//This is used if the line does not hit a circle
double angle11 = Math.atan2(origin.getY(), origin.getX());
double angle_11 = Math.atan2(origin.getY(), -origin.getX());
double angle_1_1 = angle11 + Math.PI;
double angle1_1 = angle_11 + Math.PI;
boolean noCollision = true; //Will be true if the line does not hit a circle
boolean repeat = true; //If no collision has been made the while loop stops with this
Point currentPoint = Point.copy(origin); // (x0, y0)
Point collision = new Point(-1,-1); //Stores the collision point
Point newDirection = new Point(-1,-1); //Stores the new direction after a collision, returns(magnitud, angle) of a vector
ArrayList <Point> collisionList = new ArrayList<>(); //ArrayList of collision points that will be drawn later
collisionList.add(origin); //The origin point is added as a collision for representation purposes
while(repeat == true) {
//Line equation that passes through a point with an angle
//y = a*x - a*x0 + y0; -> y = m*x + b;
double m = Math.tan(-newAngle);
double a = m;
double b = -m*currentPoint.getX() + (currentPoint.getY());
for(int i = 0; i < pointList.size(); i++) {
Point gridPoint = pointList.get(i); //(x1, y1)
//From: https://math.stackexchange.com/questions/2552687/distance-between-line-and-point
//Given a line defined as A*x + B*y + C = 0
//x*(y1-y0)+y*(x1-x0)+(-y0*(x1-x0)-x0*(y1-y0)
double A = gridPoint.getY()-currentPoint.getY();
double B = gridPoint.getX()-currentPoint.getX();
double C = -currentPoint.getY()*B + currentPoint.getX()*A;
// double d_cp_gp = Math.abs(m*gridPoint.getX()-b*(gridPoint.getY()))/(Math.sqrt(m*m + 1));
double d_cp_gp = Math.abs(A + B + C)/Math.sqrt(A*A + B*B);
if(d_cp_gp < radius) {
System.out.println("radio " + d_cp_gp);
//The intersection between a line and a circunference:
//Circunference: (x-x1)^2 + (y-y1)^2 = r^2
//Line: y = tan(alpha)*(x-x0)+y0 -> y = a*x + b; a = tan(alfa), b = -tan(alfa)*x0 + y0
//Substituting the line equation in the circunference equation:
//x^2*(1+a^2) + x*(-2x1 + 2*a*b) + 2*a*b + x1^2+b^2-r^2 = 0
double p2 = 1 + a*a;
double p1 = -2*gridPoint.getX() + 2*a*b;
double p0 = gridPoint.getX()*gridPoint.getX() + b*b - radius*radius;
double p0_ = 4*p0*p2;
System.out.println(p1*p1 + " " + p0_);
//Check if the second order equation has solutions
if(p1*p1 >= p0_) {
System.out.println("IT HAS SOLUTION");
//Solution
double root = Math.sqrt(p1*p1 - p0_);
double sol1x = (-p1 + root)/(2*p2);
double sol2x = (-p1 - root)/(2*p2);
double sol1y = a*sol1x - a*currentPoint.getX() + currentPoint.getY();
double sol2y = a*sol1x - a*currentPoint.getX() + currentPoint.getY();
//The line will intersect twice with the circle, we want the solution
//with the shortest distance to currentPoint (x0,y0)
double distSol1 = Math.sqrt(Math.pow(currentPoint.getX()- sol1x, 2) +
Math.pow(currentPoint.getY() - sol1y, 2));
double distSol2 = Math.sqrt(Math.pow(currentPoint.getX()- sol2x, 2) +
Math.pow(currentPoint.getY() - sol2y, 2));
//The collision point is the point that the line hits first
if(distSol1 < distSol2) {
collision.setXY(sol1x, sol1y);
}
else {
collision.setXY(sol2x, sol2y);
}
//newAngle returns a vector with the form (magnitude, angle)
newDirection = newAngle(currentPoint, gridPoint, collision, radius);
currentPoint = collision;
//The new line after the collision is defined here
m = Math.tan(-newDirection.getY());
a = m;
b = -m*collision.getX() + (collision.getY());
collisionList.add(collision);
System.out.println("A collision has been calculated successfully: " + collision.toString());
//If a collision
noCollision= false;
}
}
//If no collisions have been detected at the end of the for loop exit the while loop
if(i == pointList.size() - 1 && noCollision == true) {
repeat = false;
}
}
//If no collision has been calculated with the circles this
//calculates the collision with the limits of the window
if(noCollision == true && repeat == false) {
if(angle<angle11 || angle > angle1_1) {
collision.setXY(x, m*x + b);
}
else if(angle > angle11 && angle < angle_11){
collision.setXY((0 - b)/m, 0);
}
else if(angle > angle_11 && angle < angle_1_1) {
collision.setXY(0, m*0 + b);
}
else if(angle> angle_1_1 && angle < angle1_1) {
collision.setXY((y - b)/m, y);
}
collisionList.add(collision);
}
}
System.out.println("Number of collisions: " + (int)(collisionList.size() - 1));
}
My main problem is that the shortest distance to a circle doesn't seem to be calculated properly, which directly difficults if the rest of the code works properly.
I've tried different methods to find the shortest distance and this is the one that I liked the most as I find it easy to understand, however the implementation doesn't work properly. I've thought that this could be because of JavaFX coordinate system (x increases to the right and y to the bottom) but I'm not sure, I'm a bit lost at this point.
Thanks for your time.
Edit:
As suggested I am adding some extra code to facilitate reproducibility.
The Point and Vector classes are defined as follows:
public class Point {
private double x;
private double y;
public Point(double x, double y) {
this.x = x;
this.y = y;}
public double getX() {
return x;}
public double getY() {
return y;}
public void setX(double x) {
this.x = x;}
public void setY(double y) {
this.y = y;}
public void setXY(double x, double y) {
this.x = x;
this.y = y;}
#Override
public String toString() {
return("(" + this.x + "," + this.y + ")");
}
public static Point copy(Point a) {
return new Point(a.getX(), a.getY());
}
}
public class Vector {
private double vx;
private double vy;
private double ptoApX;
private double ptoApY;
private double angle;
private double modulo;
public Vector(double vx, double vy) {
this.vx = vx;
this.vy = vy;
this.ptoApX = 0;
this.ptoApY = 0;
this.angle = angle(vx,vy);
this.modulo = modulo(vx,vy);
}
//Getters
public double getVx() {
return this.vx;
}
public double getVy() {
return this.vy;
}
public double getPtoApX() {
return this.ptoApX;
}
public double getPtoApY() {
return this.ptoApY;
}
public double getAngle() {
return this.angle;
}
public double getModulo() {
return this.modulo;
}
//Setters
public void setVx(double vx) {
this.vx = vx;
}
public void setVy(double vy) {
this.vy = vy;
}
public void setPtoApX(double ptoApX) {
this.ptoApX = ptoApX;
}
public void setPtoApY(double ptoApY) {
this.ptoApY = ptoApY;
}
public void setAngle(double angle) {
this.angle = angle;
}
public void setModulo(double modulo) {
this.modulo = modulo;
}
//To String
#Override
public String toString() {
return "("+this.getVx()+","+this.getVy()+")";
}
public static double dotProduct(Vector a, Vector b) {
return a.getVx()*b.getVx() + a.getVy()*b.getVy();
}
public static Vector escalarProduct(Vector v, double n) {
return new Vector(n*v.getVx(), n*v.getVy());
}
public static Vector vectorWith2Points(Point a, Point b) {
Point p = Point.resta(a,b);
return new Vector(p.getX(),p.getY());
}
public static Vector vectorPointAngle(Point a, double angle, double modulo) {
double angleRadians = Math.toRadians(angle);
Point b = new Point(Math.cos(angleRadians)*modulo, Math.sin(angleRadians)*modulo);
return vectorWith2Points(a,b);
}
public static double modulo(double vx, double vy) {
return Math.sqrt(vx*vx + vy*vy);
}
public static double angle(double vx, double vy) {
return Math.atan2(vy, vx);
}
public static Vector normalize(Vector v) {
return new Vector(v.getVx()/v.getModulo(),v.getVy()/v.getModulo());
}
public static double angle2vectors(Vector u, Vector v) {
double argument = dotProduct(u,v)/(u.getModulo()*v.getModulo());
return Math.acos(argument);
}
public static Point polar2cart(double r, double angle) {
return new Point(r*Math.cos(angle), r*Math.sin(angle));
}
public static Point cart2polar(Point p) {
return new Point(modulo(p.getX(), p.getY()), angle(p.getX(), p.getY()));
}
}
And the method to obtain the new angle after a collision:
private Point newAngle(Point origin, Point center, Point c, double radius) {
//Normal vector
Vector n = Vector.vectorWith2Points(c, center);
Vector nNorm = Vector.normalize(n);
//Incident vector
Vector d = Vector.vectorWith2Points(c, origin);
//Tangent vector
Vector tg = new Vector(-nNorm.getVy(), nNorm.getVx());
//Reflected vector
double product = Vector.dotProduct(d,tg);
Vector r = new Vector(d.getVx()-2*product*tg.getVx(),
d.getVy() - 2*product*tg.getVy());
return new Point(r.getModulo(), r.getAngle());
}
An example of the code of different angles where a collision should be detected:
double x = 600;
double y = 400;
double radius = 10;
Point origin = new Point(x/2, y/2);
ArrayList<Point> pointList = new ArrayList<>();
pointList.add(new Point(40,40));
pointList.add(new Point(500,100));
pointList.add(new Point(40,330));
pointList.add(new Point(450,300));
//This should return a solution
extendPoint(0.4363323129985824, origin, x, y, radius, pointList);
extendPoint(2.6179938779914944, origin, x, y, radius, pointList);
//this returns a solution when it should not
extendPoint(1.5707963267948966, origin, x, y, radius, pointList);
extendPoint(-1.5707963267948966, origin, x, y, radius, pointList);
I wrote an class with everything needed to run the code here: https://pastebin.com/wMjUh9pZ
I think you should create a class that represents an intersection by a ray.
class Intersection{
double distance;
Point loc;
double normal;
}
That way, distance is along the ray and normal is the normal of the object intersected.
Then I would have a method for finding the intersetion of a circle and a point.
List<Intersection> lineAndCircle( Point org, double angle, Point center, double radius){...}
You seem to have a similar method but you're doing more work in it.
Then you also want to check the edge of the screen.
Intersection lineAndBoundary( Point org, double angle){ ... }
You have a very similar method, but you seem to be doing a lot more work in the method. . This way you are testing separate methods. Then your algorithm works as.
1 go through circles and find intersections.
2 get the intersection with the boundary.
3 find the closest intersection ( the smallest distance greater than 0 )
Doing it this way makes it a bit more extensible. First our ray is re-used a lot. Lets make a class.
class Ray{
Point origin;
double angle;
}
Then we collide a ray with multiple objects.
interface Interceptable{
List<Intersection> intercepts(Ray r);
}
Then we can use different classes.
class Circle implements Interceptable{
Point pos;
double radius;
#Override
List<Intersection> collides(Ray r){
...
}
}
Now you can right collides and testable.
Circle a = new Circle( new Point( 40, 40 ), 5 );
List<Intersection> yes = a.collides( new Ray( new Point(0, 0), 3.14/4 ) );
List<Intersection> no = a.collides( new Ray( new Point(0, 0), 0) ) );
Then you can narrow your example down to. "How do I write a collide method?" or "Why doesn't my collide method work for this ray/circle pair? I expect it to hit at two points, but it misses." etc.
Here is a complete runnable example that creates a swing window. I kinda enjoy making toy programs like this.
Note that I used an interface for the Intersectable. So now it is circles, but it could be anything that returns a list of Intersection
import javax.swing.*;
import java.awt.Graphics;
import java.awt.Dimension;
import java.awt.Color;
import java.awt.event.*;
import java.util.*;
public class RayAndCircle{
public static void main(String[] args){
List<Intersectable> circles = new ArrayList<>();
for(int i = 0; i<250; i++){
double r = Math.random()*50 + 50;
double x = 2048*Math.random();
double y = 2048*Math.random();
circles.add( new Circle( r, new double[]{x,y}));
}
List<LineSegment> segments = new ArrayList<>();
JFrame frame = new JFrame("Ray caster");
JPanel panel = new JPanel(){
#Override
public Dimension getPreferredSize(){
return new Dimension(2048, 2048);
}
#Override
public void paintComponent( Graphics g){
g.setColor(Color.RED);
for( Intersectable c: circles ){
c.draw(g);
}
g.setColor(Color.BLACK);
for( LineSegment segment: segments){
g.drawLine( (int) segment.a[0], (int) segment.a[1],(int)segment.b[0], (int)segment.b[1]);
}
}
};
panel.addMouseListener( new MouseAdapter(){
#Override
public void mouseClicked( MouseEvent evt ){
double x = evt.getPoint().getX();
double y = evt.getPoint().getY();
double theta = Math.random() * Math.PI * 2;
double dx = Math.cos( theta );
double dy = Math.sin( theta );
Ray ray = new Ray( new double[] {x, y}, new double[]{ dx, dy } );
int count = 500;
Intersectable last = null;
while( ray != null && count > 0 ){
Intersection hit = null;
Intersectable next = null;
for(Intersectable c: circles){
if(c == last){
continue;
}
List<Intersection> intersections = c.intersects(ray);
for(Intersection i : intersections){
if( hit == null ){
hit = i;
next = c;
} else{
if( hit.s > i.s ){
hit = i;
next = c;
}
}
}
}
if(hit != null){
last = next;
segments.add( new LineSegment( ray.origin, new double[]{ hit.pos[0], hit.pos[1] } ) );
count--;
//reflected portion of ray.
double dot = hit.normal[0]*ray.direction[0] + hit.normal[1]*ray.direction[1];
double rx = ray.direction[0] - 2 * hit.normal[0]*dot;
double ry = ray.direction[1] - 2 * hit.normal[1]*dot;
double z = Math.sqrt(rx*rx + ry*ry);
ray = new Ray(hit.pos, new double[] { rx/z, ry/z});
} else{
ray = null;
}
}
panel.repaint();
}
});
frame.setContentPane(panel);
frame.pack();
frame.setVisible(true);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}
class Ray{
double[] origin; double[] direction;
public Ray( double[] origin, double[] direction){
this.origin = new double[]{origin[0], origin[1]};
this.direction = new double[]{direction[0], direction[1]};
}
}
class Intersection{
double s;
double[] pos;
double[] normal;
Circle b;
public Intersection(double s, double[] pos, double[] normal){
this.s = s;
this.pos = pos;
setNormal(normal);
}
public void setNormal(double[] normal){
double m = Math.sqrt(normal[0]*normal[0] + normal[1]*normal[1]);
if( Double.isNaN(m) || m == 0) throw new RuntimeException("Invalid normal! Magnitude of" + m);
this.normal = new double[] { normal[0]/m , normal[1]/m };
}
}
interface Intersectable{
List<Intersection> intersects(Ray ray);
void draw(Graphics g);
}
class Circle implements Intersectable{
double[] origin;
double radius;
public Circle( double radius, double[] origin){
this.radius = radius;
this.origin = new double[]{origin[0], origin[1]};
}
Intersection intersectionAt(Ray ray, double s){
//intersection.
double locx = ray.origin[0] + s*ray.direction[0];
double locy = ray.origin[1] + s*ray.direction[1];
double nx = (locx - origin[0])/radius;
double ny = (locy - origin[1])/radius;
return new Intersection( s, new double[]{ locx, locy }, new double[]{nx, ny} );
}
public List<Intersection> intersects(Ray ray){
double rx = origin[0] - ray.origin[0];
double ry = origin[1] - ray.origin[1];
double m2 = rx*rx + ry*ry;
double m = Math.sqrt(m2);
//position along ray that is closest to circles origin.
double s = rx*ray.direction[0] + ry*ray.direction[1];
//closest distance to circle.
double approach = Math.sqrt(m2 - s*s);
List<Intersection> result = new ArrayList<>();
if( approach < radius ){
//two intersections at points on circle.
//radius is hypotenuse and approach is one of the lengths.
double l = Math.sqrt( radius*radius - approach*approach);
double s1 = s - l;
if(s1 > 0){
result.add( intersectionAt(ray, s1) );
}
double s2 = s + l;
if(s2 > 0){
//intersection!
result.add(intersectionAt(ray, s2) );
}
} else if(approach == radius){
//one intersection tangent.
if( s > 0 ){
result.add( intersectionAt(ray, s) );
}
} else{
//miss.
}
return result;
}
public void draw(Graphics g){
g.fillOval(
(int)(origin[0] - radius),
(int)(origin[1] - radius),
(int)radius*2,
(int)radius*2
);
}
}
class LineSegment{
double[] a, b;
public LineSegment( double[] a, double[] b){
this.a = new double[]{a[0], a[1]};
this.b = new double[]{b[0], b[1]};
}
}
You'll probably be most interested in the intersects method of the Circle class, and the small chunk of code burried in the mouseClicked method that calculates the reflected ray.
If you only want to know if the line intersects if a given circle, create a second line which originates at the center of the given circle and the direction is the direction of your initial line rotated by 90 degrees. Then compute the intersection of the two lines. If then the distance between the intersection point and the center of the circle is smaller then the radius, both intersect.
A while ago I wrote a small Geometry lib, I striped out the sections which are relevant for you, here is my code:
Line class
public class Line {
final Vector2D positionVector;
final Vector2D directionVector;
public Line(final Vector2D positionVector, final Vector2D directionVector) {
this.positionVector = positionVector;
this.directionVector = directionVector;
}
public OptionalDouble computeIntersection(final Line line) {
final double numerator = line.getPositionVector().subtract(this.positionVector).cross(this.directionVector);
final double denominator = this.directionVector.cross(line.directionVector);
if (Math.abs(numerator) < 1e-10 && Math.abs(denominator) < 1e-10) {
// collinear
return OptionalDouble.of(Double.POSITIVE_INFINITY);
} else if (Math.abs(denominator) < 1e-10) {
// parallel
return OptionalDouble.empty(); // Lines are parallel.
}
final double t = line.getPositionVector().subtract(this.positionVector).cross(line.directionVector) / denominator;
return OptionalDouble.of(t);
}
public Vector2D getPositionVector() {
return positionVector;
}
public Vector2D getDirectionVector() {
return directionVector;
}
public Point2D getClosestPointOnLine(final Point2D point) {
final Line line = new Line(new Vector2D(point.getX(), point.getY()), this.directionVector.turn90DegreeClockwise());
final OptionalDouble intersection = this.computeIntersection(line);
final Vector2D result = this.positionVector.add(this.directionVector.lerp(intersection.getAsDouble()));
return new Point2D(result.getX(), result.getY());
}
}
intersection function
public static PointResult intersection(final Line l1, final Circle c1) {
final Point2D intersection = l1.getClosestPointOnLine(c1.getCenter());
final double dist = intersection.distance(c1.getCenter());
if (Math.abs(dist - c1.getRadius()) < 1e-10) {
final List<Point2D> result = new LinkedList<>();
result.add(intersection);
return new PointResult(Collections.unmodifiableList(result));
} else if (dist < c1.getRadius()) {
// we have two points
final double adjacentLeg = Math.sqrt(c1.getRadius() * c1.getRadius() - dist * dist);
final Point2D pt1 = intersection.pointAt(l1.getDirectionVector().angle(), adjacentLeg);
final Point2D pt2 = intersection.pointAt(l1.getDirectionVector().angle() + Math.PI, adjacentLeg);
final List<Point2D> result = new LinkedList<>();
result.add(pt1);
result.add(pt2);
return new PointResult(Collections.unmodifiableList(result));
}
return new PointResult();
}
TestCase
#Test
void testIntersectionLineCircleTwoPoints() {
final Point2D ptCircleCenter = new Point2D(2.0, 5.0);
final Point2D ptLineCircleIntersection = new Point2D(5.0, 2.0);
final Point2D pt1 = new Point2D(3.0, 0.0);
final Point2D pt2 = new Point2D(7.0, 4.0);
final double a = Math.sqrt((2.0 * 2.0) + (2.0 * 2.0));
final double b = ptCircleCenter.diff(ptLineCircleIntersection).norm();
final double radius = Math.sqrt((a * a) + (b * b));
final Line l1 = new Line(pt1, pt2);
final Circle circle = new Circle(ptCircleCenter, radius);
PointResult intersection = GeometryOperation.intersection(l1, circle);
assertTrue(intersection.getPoints().isPresent());
assertEquals(2, intersection.getPoints().get().size());
assertEquals(7.0, intersection.getPoints().get().get(0).getX(), 1e-10);
assertEquals(4.0, intersection.getPoints().get().get(0).getY(), 1e-10);
assertEquals(3.0, intersection.getPoints().get().get(1).getX(), 1e-10);
assertEquals(0.0, intersection.getPoints().get().get(1).getY(), 1e-10);
}
I did not add the Circle, Vector2D and Point2D class because they are trivial. And the class PointResult is just a list.
How can I fix the multiplication error?
The formula is inside the nested class Area1 and I can't get the total value or product given by the user
I've tried giving it a value like:
side1 = 0;
or
side1 = 1;
The answer is always equal to 0
public void getArea(){
int area = side1 * side2;
System.out.println("Area of square: " + area);
Area1 square = new Area1(side1,side2);
square.getArea();
import java.util.Scanner;
public class Area1 {
int side1;
int side2;
int height;
int base;
int width;
int length;
Area1 (int side1,int side2,int height,int base, int width, int length){
this.side1 = side1;
this.side2 = side2;
this.width = width;
this.length = length;
}
private Area1(int height, int base) {
this.height = height;
this.base = base;
}
public void getArea(){
int area = side1 * side2;
System.out.println("Area of square: " + area);
}
public void getArea1(){
int area2 = height * base / 2;
System.out.println("Area of triangle: " + area2);
}
public void getArea2(){
int area2 = width * length;
System.out.println("Area of rectangle: " + area2);
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
int side1 = 0;
int side2 = 0;
int height;
int base;
int width;
int length;
System.out.println("-----FOR SQUARE-----");
System.out.println("Please enter 1st side of square: ");
side1 = input.nextInt();
System.out.println("Please enter 2nd side of square: ");
side2 = input.nextInt();
System.out.println("-----FOR TRIANGLE-----");
System.out.println("Please enter height of triangle: ");
height = input.nextInt();
System.out.println("Please enter base of triangle: ");
base = input.nextInt();
System.out.println("-----FOR RECTANGLE-----");
System.out.println("Please enter width of rectangle: ");
width = input.nextInt();
System.out.println("Please enter length of rectangle: ");
length = input.nextInt();
System.out.println("=====THE RESULTS ARE=====");
Area1 square = new Area1(side1,side2);
square.getArea();
Area1 triangle = new Area1(height, base);
triangle.getArea1();
Area1 rectangle = new Area1(width,length);
rectangle.getArea2();
}
}
The solution is simple:
You are setting only two properties (you are using single constructor only):
private Area1(int height, int base) {
this.height = height;
this.base = base;
}
So you are setting only two fields.
And in our compute methods you are using other fields, that are not set. And because they are primitive types, they are set to zero. Youn need to use other full arg constructor.
This is a great candidate for object oriented programming:
abstract class Figure {
abstract void getArea();
}
public class Square extends Figure {
private final int side1;
private final int side2;
Square(int side1, int side2) {
this.side1 = side1;
this.side2 = side2;
}
#Override
void getArea() {
int area = side1 * side2;
System.out.println("Area of square: " + area);
}
}
public class Triangle extends Figure {
private final int base;
private final int height;
Triangle(int base, int height) {
this.base = base;
this.height = height;
}
#Override
void getArea() {
int area2 = height * base / 2;
System.out.println("Area of triangle: " + area2);
}
}
And now you can compute:
System.out.println("=====THE RESULTS ARE=====");
Figure square = new Square(side1, side2);
square.getArea();
Figure triangle = new Triangle(height, base);
triangle.getArea();
With this approach you will not have to multiple variables if new figure will be added. You will not have to struggle with large constructor. Lastly: you are using only few fields for each figure, rest is useless.
The issue is that, in the constructor you assign the values only for height and base.
private Area1(int height, int base) {
this.height = height;
this.base = base;
}
When you call this,
Area1 square = new Area1(side1,side2);
square.getArea();
the getArea() method looks for the variables side1 and side2. But you have set the variables height and base only. So, the variables side1 and side2 have the value 0 by default.
Possible solution:
You should probably initialize the objects with the other constructor method that you already have, that uses all the variables, like
Area1 square = new Area1(side1,side2,0,0,0,0);
square.getArea();
Area1 triangle = new Area1(0, 0, height, base, 0, 0);
triangle.getArea1();
Area1 rectangle = new Area1(0,0,0,0,width,length);
rectangle.getArea2();
You made mistake in your parameterize constructor as you assign side1 and side2 value to this.height = height; this.base = base; and you trying to multiply side1 and side2 which has default value only.
private Area1(int side1, int side2) {
this.side1 = side1;
this.side2 = side2;
}
This is the code I have done so far. It creates the ArrayList and adds the circles. The volume is stored and is printed in the console. The last thing I have to do is print out the smallest volume using a for-each loop. This is where I'm having difficulties. I could really use some help/advice
public static void main(String[] args)
{
Random rand = new Random();
final int RADIUS_MAX = 100;
int NUM_SPHERES = 4;
List<Sphere> spheres = new ArrayList<Sphere>();
for(int add = 1; add <= NUM_SPHERES; add++) {
spheres.add(new Sphere(rand.nextInt(RADIUS_MAX)));
}
for (Sphere s : spheres) {
System.out.println(s);
}
//TODO: Convert to a for-each loop to find the volume of the smallest sphere
for (Sphere s : spheres) {
}
}
You do not need an additional loop. The sphere with the smallest radius will have the smallest volume. You could store the smallest volume so far (initialized to a very large volume) and update it in either of your existing loops. I believe the formula for volume is (4. / 3) * Math.PI * Math.pow(radius, 3).
The volume formula of the sphere depends from radius like V <=> R, so no need to calculate volume each time, because minimal voule will be with minimal radius.
public class Foo {
public static void main(String... args) {
Random rand = new Random();
final int maxRadius = 100;
final int totalSphere = 4;
List<Sphere> spheres = new ArrayList<>();
for (int i = 0; i < totalSphere; i++)
spheres.add(new Sphere(rand.nextInt(maxRadius)));
for (Sphere sphere : spheres)
System.out.println(sphere);
Sphere smallestSphere = spheres.get(0);
for (Sphere sphere : spheres)
if (smallestSphere == null || sphere.compareTo(smallestSphere) < 0)
smallestSphere = sphere;
System.out.println("smallest volume: " + smallestSphere.getVolume());
}
public static class Sphere implements Comparable<Sphere> {
private final int radius;
public Sphere(int radius) {
this.radius = radius;
}
public double getVolume() {
return (4. / 3) * Math.PI * Math.pow(radius, 3);
}
#Override
public String toString() {
return "radius: " + radius;
}
#Override
public int compareTo(Sphere sphere) {
return Integer.compare(radius, sphere.radius);
}
}
}
I have a method called perimeter that is supposed to take in some points and return the perimeter of the polygon based upon the points provided. I keep getting the wrong answer for perimeter when I use a tester to run the program.
import java.util.ArrayList;
import java.awt.geom.Point2D;
import java.awt.geom.Point2D.Double;
/**A class that represents a geometric polygon. Methods are provided for adding
* a point to the polygon and for calculating the perimeter and area of the
* polygon.
*/
class MyPolygon {
//list of the points of the polygon
private ArrayList<Point2D.Double> points;
/**Constructs a polygon with no points in it.
*/
public MyPolygon() {
points = new ArrayList<Point2D.Double>();
}
/**Adds a point to the end of the list of points in the polygon.
* #param x The x coordinate of the point.
* #param y The y coordinate of the point.
*/
public void add(double x, double y) {
points.add(new Point2D.Double(x,y));
}
/**Calculates and returns the perimeter of the polygon.
* #return 0.0 if < 2 points in polygon, otherwise returns the
* sum of the lengths of the line segments.
*/
public double perimeter() {
if (points.size() < 2){
return 0.0;
}
int i = 0;
double d = 0;
double total = 0;
while (i < points.size() - 1 )
{
Point2D.Double point1 = points.get(i);
double x = point1.x;
double y = point1.y;
Point2D.Double point2 = points.get(i+1);
double x1 = point2.x;
double y1 = point2.y;
d = point1.distance(point2);
System.out.println(d);
//d = Math.sqrt(Math.pow(x1 - x,2) + Math.pow(y1 - y, 2));
total = total + d;
i++;
}
return total;
}
/**Calculates and returns the area of the polygon.
* #return 0.0 if < 3 points in the polygon, otherwise returns
* the area of the polygon.
*/
public double area() {
return 0;
}
}
The Tester class:
class PolygonTester {
public static void main(String args[]) {
MyPolygon poly = new MyPolygon();
poly.add(1.0,1.0);
poly.add(3.0,1.0);
poly.add(1.0,3.0);
System.out.println(poly.perimeter());
System.out.println(poly.area());
}
}
you should initialize total variable with lenght of last edge:
double total = points.get(0).distance(poinsts.get(points.size() - 1));
//Implement a subclass Square that extends the Rectangle class. In the constructor,
accept the x- and y-positions of the center and the side length of the square. Call the
setLocation and setSize methods of the Rectangle class. Look up these methods in the
documentation for the Rectangle class. Also supply a method getArea that computes
and returns the area of the square. Write a sample program that asks for the center
and side length, then prints out the square (using the toString method that you
inherit from Rectangle) and the area of the square.
//Ok... So this is last minute, but I don't understand what is wrong with my code it is giving me the error that square cannot be resolved to a type... So here is my Class:
import java.awt.Rectangle;
public class Squares22 extends Rectangle
{
public Squares22(int x, int y, int length) {
setLocation(x - length / 2, y - length / 2);
setSize(length, length);
}
public int getArea() {
return (int) (getWidth() * getHeight());
}
public String toString() {
int x = (int) getX();
int y = (int) getY();
int w = (int) getWidth();
int h = (int) getHeight();
return "Square[x=" + x + ",y=" + y + ",width=" + w + ",height=" + h
+ "]";
}
}
//And this is my tester class...
import java.util.Scanner;
public class Squares22Tester
{
public static void main(String[] args)
{
Scanner newScanx = new Scanner(System.in);
Scanner newScany = new Scanner(System.in);
Scanner newScanl = new Scanner(System.in);
System.out.println("Enter x:");
String x2 = newScanx.nextLine();
System.out.println("Enter y:");
String y2 = newScany.nextLine();
System.out.println("Enter length:");
String l2 = newScanl.nextLine();
int x = Integer.parseInt(x2);
int y = Integer.parseInt(y2);
int length = Integer.parseInt(l2);
Square sq = new Square(x, y, length);
System.out.println(sq.toString());
}
}
//Can anyone please help my assignment is due at midnight.. It says square cannot be resolved to a type on the tester class when compliling....
Square isn't the name of your class. The name of the class is 'Squares22'. This is why 'Square' cannot be recognized.
Change Square in the test to Squares22 or vice versa. This should solve your issues.