Below is the syntax highlighted version of Point2D.java
from §1.2 Data Abstraction.
/****************************************************************************** * Compilation: javac Point2D.java * Execution: java Point2D x0 y0 n * Dependencies: StdDraw.java StdRandom.java * * Immutable point data type for points in the plane. * ******************************************************************************/ import java.util.Arrays; import java.util.Comparator; /** * The {@code Point} class is an immutable data type to encapsulate a * two-dimensional point with real-value coordinates. * <p> * Note: in order to deal with the difference behavior of double and * Double with respect to -0.0 and +0.0, the Point2D constructor converts * any coordinates that are -0.0 to +0.0. * <p> * For additional documentation, * see <a href="https://algs4.cs.princeton.edu/12oop">Section 1.2</a> of * <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne. * * @author Robert Sedgewick * @author Kevin Wayne */ public final class Point2D implements Comparable<Point2D> { /** * Compares two points by x-coordinate. */ public static final Comparator<Point2D> X_ORDER = new XOrder(); /** * Compares two points by y-coordinate. */ public static final Comparator<Point2D> Y_ORDER = new YOrder(); /** * Compares two points by polar radius. */ public static final Comparator<Point2D> R_ORDER = new ROrder(); private final double x; // x coordinate private final double y; // y coordinate /** * Initializes a new point (x, y). * @param x the x-coordinate * @param y the y-coordinate * @throws IllegalArgumentException if either {@code x} or {@code y} * is {@code Double.NaN}, {@code Double.POSITIVE_INFINITY} or * {@code Double.NEGATIVE_INFINITY} */ public Point2D(double x, double y) { if (Double.isInfinite(x) || Double.isInfinite(y)) throw new IllegalArgumentException("Coordinates must be finite"); if (Double.isNaN(x) || Double.isNaN(y)) throw new IllegalArgumentException("Coordinates cannot be NaN"); if (x == 0.0) this.x = 0.0; // convert -0.0 to +0.0 else this.x = x; if (y == 0.0) this.y = 0.0; // convert -0.0 to +0.0 else this.y = y; } /** * Returns the x-coordinate. * @return the x-coordinate */ public double x() { return x; } /** * Returns the y-coordinate. * @return the y-coordinate */ public double y() { return y; } /** * Returns the polar radius of this point. * @return the polar radius of this point in polar coordinates: sqrt(x*x + y*y) */ public double r() { return Math.sqrt(x*x + y*y); } /** * Returns the angle of this point in polar coordinates. * @return the angle (in radians) of this point in polar coordinates (between –π and π) */ public double theta() { return Math.atan2(y, x); } /** * Returns the angle between this point and that point. * @return the angle in radians (between –π and π) between this point and that point (0 if equal) */ private double angleTo(Point2D that) { double dx = that.x - this.x; double dy = that.y - this.y; return Math.atan2(dy, dx); } /** * Returns true if a→b→c is a counterclockwise turn. * @param a first point * @param b second point * @param c third point * @return { -1, 0, +1 } if a→b→c is a { clockwise, collinear; counterclockwise } turn. */ public static int ccw(Point2D a, Point2D b, Point2D c) { double area2 = (b.x-a.x)*(c.y-a.y) - (b.y-a.y)*(c.x-a.x); if (area2 < 0) return -1; else if (area2 > 0) return +1; else return 0; } /** * Returns twice the signed area of the triangle a-b-c. * @param a first point * @param b second point * @param c third point * @return twice the signed area of the triangle a-b-c */ public static double area2(Point2D a, Point2D b, Point2D c) { return (b.x-a.x)*(c.y-a.y) - (b.y-a.y)*(c.x-a.x); } /** * Returns the Euclidean distance between this point and that point. * @param that the other point * @return the Euclidean distance between this point and that point */ public double distanceTo(Point2D that) { double dx = this.x - that.x; double dy = this.y - that.y; return Math.sqrt(dx*dx + dy*dy); } /** * Returns the square of the Euclidean distance between this point and that point. * @param that the other point * @return the square of the Euclidean distance between this point and that point */ public double distanceSquaredTo(Point2D that) { double dx = this.x - that.x; double dy = this.y - that.y; return dx*dx + dy*dy; } /** * Compares two points by y-coordinate, breaking ties by x-coordinate. * Formally, the invoking point (x0, y0) is less than the argument point (x1, y1) * if and only if either {@code y0 < y1} or if {@code y0 == y1} and {@code x0 < x1}. * * @param that the other point * @return the value {@code 0} if this string is equal to the argument * string (precisely when {@code equals()} returns {@code true}); * a negative integer if this point is less than the argument * point; and a positive integer if this point is greater than the * argument point */ public int compareTo(Point2D that) { if (this.y < that.y) return -1; if (this.y > that.y) return +1; if (this.x < that.x) return -1; if (this.x > that.x) return +1; return 0; } /** * Compares two points by polar angle (between 0 and 2π) with respect to this point. * * @return the comparator */ public Comparator<Point2D> polarOrder() { return new PolarOrder(); } /** * Compares two points by atan2() angle (between –π and π) with respect to this point. * * @return the comparator */ public Comparator<Point2D> atan2Order() { return new Atan2Order(); } /** * Compares two points by distance to this point. * * @return the comparator */ public Comparator<Point2D> distanceToOrder() { return new DistanceToOrder(); } // compare points according to their x-coordinate private static class XOrder implements Comparator<Point2D> { public int compare(Point2D p, Point2D q) { return Double.compare(p.x, q.x); } } // compare points according to their y-coordinate private static class YOrder implements Comparator<Point2D> { public int compare(Point2D p, Point2D q) { return Double.compare(p.y, q.y); } } // compare points according to their polar radius private static class ROrder implements Comparator<Point2D> { public int compare(Point2D p, Point2D q) { double delta = (p.x*p.x + p.y*p.y) - (q.x*q.x + q.y*q.y); return Double.compare(delta, 0); } } // compare other points relative to atan2 angle (between -pi/2 and pi/2) they make with this Point private class Atan2Order implements Comparator<Point2D> { public int compare(Point2D q1, Point2D q2) { double angle1 = angleTo(q1); double angle2 = angleTo(q2); return Double.compare(angle1, angle2); } } // compare other points relative to polar angle (between 0 and 2pi) they make with this Point private class PolarOrder implements Comparator<Point2D> { public int compare(Point2D q1, Point2D q2) { double dx1 = q1.x - x; double dy1 = q1.y - y; double dx2 = q2.x - x; double dy2 = q2.y - y; if (dy1 >= 0 && dy2 < 0) return -1; // q1 above; q2 below else if (dy2 >= 0 && dy1 < 0) return +1; // q1 below; q2 above else if (dy1 == 0 && dy2 == 0) { // 3-collinear and horizontal if (dx1 >= 0 && dx2 < 0) return -1; else if (dx2 >= 0 && dx1 < 0) return +1; else return 0; } else return -ccw(Point2D.this, q1, q2); // both above or below // Note: ccw() recomputes dx1, dy1, dx2, and dy2 } } // compare points according to their distance to this point private class DistanceToOrder implements Comparator<Point2D> { public int compare(Point2D p, Point2D q) { double dist1 = distanceSquaredTo(p); double dist2 = distanceSquaredTo(q); return Double.compare(dist1, dist2); } } /** * Compares this point to the specified point. * * @param other the other point * @return {@code true} if this point equals {@code other}; * {@code false} otherwise */ @Override public boolean equals(Object other) { if (other == this) return true; if (other == null) return false; if (other.getClass() != this.getClass()) return false; Point2D that = (Point2D) other; return this.x == that.x && this.y == that.y; } /** * Return a string representation of this point. * @return a string representation of this point in the format (x, y) */ @Override public String toString() { return "(" + x + ", " + y + ")"; } /** * Returns an integer hash code for this point. * @return an integer hash code for this point */ @Override public int hashCode() { int hashX = ((Double) x).hashCode(); int hashY = ((Double) y).hashCode(); return 31*hashX + hashY; } /** * Plot this point using standard draw. */ public void draw() { StdDraw.point(x, y); } /** * Plot a line from this point to that point using standard draw. * @param that the other point */ public void drawTo(Point2D that) { StdDraw.line(this.x, this.y, that.x, that.y); } /** * Unit tests the point data type. * * @param args the command-line arguments */ public static void main(String[] args) { int x0 = Integer.parseInt(args[0]); int y0 = Integer.parseInt(args[1]); int n = Integer.parseInt(args[2]); StdDraw.setCanvasSize(800, 800); StdDraw.setXscale(0, 100); StdDraw.setYscale(0, 100); StdDraw.setPenRadius(0.005); StdDraw.enableDoubleBuffering(); Point2D[] points = new Point2D[n]; for (int i = 0; i < n; i++) { int x = StdRandom.uniformInt(100); int y = StdRandom.uniformInt(100); points[i] = new Point2D(x, y); points[i].draw(); } // draw p = (x0, x1) in red Point2D p = new Point2D(x0, y0); StdDraw.setPenColor(StdDraw.RED); StdDraw.setPenRadius(0.02); p.draw(); // draw line segments from p to each point, one at a time, in polar order StdDraw.setPenRadius(); StdDraw.setPenColor(StdDraw.BLUE); Arrays.sort(points, p.polarOrder()); for (int i = 0; i < n; i++) { p.drawTo(points[i]); StdDraw.show(); StdDraw.pause(100); } } }