edu.princeton.cs.algs4

Class Point2D

java.lang.Object

edu.princeton.cs.algs4.Point2D

All Implemented Interfaces:

java.lang.Comparable<Point2D>

public final class Point2D
extends java.lang.Object
implements java.lang.Comparable<Point2D>

The Point class is an immutable data type to encapsulate a two-dimensional point with real-value coordinates.

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.

For additional documentation, see Section 1.2 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Field Summary

Fields

Modifier and Type	Field and Description
static java.util.Comparator<Point2D>	R_ORDER Compares two points by polar radius.
static java.util.Comparator<Point2D>	X_ORDER Compares two points by x-coordinate.
static java.util.Comparator<Point2D>	Y_ORDER Compares two points by y-coordinate.

Constructor Summary

Constructors

Constructor and Description
Point2D(double x, double y) Initializes a new point (x, y).

Method Summary

Modifier and Type	Method and Description
static double	area2(Point2D a, Point2D b, Point2D c) Returns twice the signed area of the triangle a-b-c.
java.util.Comparator<Point2D>	atan2Order() Compares two points by atan2() angle (between –π and π) with respect to this point.
static int	ccw(Point2D a, Point2D b, Point2D c) Returns true if a→b→c is a counterclockwise turn.
int	compareTo(Point2D that) Compares two points by y-coordinate, breaking ties by x-coordinate.
double	distanceSquaredTo(Point2D that) Returns the square of the Euclidean distance between this point and that point.
double	distanceTo(Point2D that) Returns the Euclidean distance between this point and that point.
java.util.Comparator<Point2D>	distanceToOrder() Compares two points by distance to this point.
void	draw() Plot this point using standard draw.
void	drawTo(Point2D that) Plot a line from this point to that point using standard draw.
boolean	equals(java.lang.Object other) Compares this point to the specified point.
int	hashCode() Returns an integer hash code for this point.
static void	main(java.lang.String[] args) Unit tests the point data type.
java.util.Comparator<Point2D>	polarOrder() Compares two points by polar angle (between 0 and 2π) with respect to this point.
double	r() Returns the polar radius of this point.
double	theta() Returns the angle of this point in polar coordinates.
java.lang.String	toString() Return a string representation of this point.
double	x() Returns the x-coordinate.
double	y() Returns the y-coordinate.

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Detail

X_ORDER

public static final java.util.Comparator<Point2D> X_ORDER

Compares two points by x-coordinate.

Y_ORDER

public static final java.util.Comparator<Point2D> Y_ORDER

Compares two points by y-coordinate.

R_ORDER

public static final java.util.Comparator<Point2D> R_ORDER

Compares two points by polar radius.

Constructor Detail

Point2D

public Point2D(double x,
               double y)

Initializes a new point (x, y).

Parameters:

x - the x-coordinate

y - the y-coordinate

Throws:

java.lang.IllegalArgumentException - if either x or y is Double.NaN, Double.POSITIVE_INFINITY or Double.NEGATIVE_INFINITY

Method Detail

x

public double x()

Returns the x-coordinate.

Returns:

the x-coordinate

y

public double y()

Returns the y-coordinate.

Returns:

the y-coordinate

r

public double r()

Returns the polar radius of this point.

Returns:

the polar radius of this point in polar coordiantes: sqrt(x*x + y*y)

theta

public double theta()

Returns the angle of this point in polar coordinates.

Returns:

the angle (in radians) of this point in polar coordiantes (between –π and π)

ccw

public static int ccw(Point2D a,
                      Point2D b,
                      Point2D c)

Returns true if a→b→c is a counterclockwise turn.

Parameters:

a - first point

b - second point

c - third point

Returns:

{ -1, 0, +1 } if a→b→c is a { clockwise, collinear; counterclocwise } turn.

area2

public static double area2(Point2D a,
                           Point2D b,
                           Point2D c)

Returns twice the signed area of the triangle a-b-c.

Parameters:

a - first point

b - second point

c - third point

Returns:

twice the signed area of the triangle a-b-c

distanceTo

public double distanceTo(Point2D that)

Returns the Euclidean distance between this point and that point.

Parameters:

that - the other point

Returns:

the Euclidean distance between this point and that point

distanceSquaredTo

public double distanceSquaredTo(Point2D that)

Returns the square of the Euclidean distance between this point and that point.

Parameters:

that - the other point

Returns:

the square of the Euclidean distance between this point and that point

compareTo

public int compareTo(Point2D that)

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 y0 < y1 or if y0 == y1 and x0 < x1.

Specified by:

compareTo in interface java.lang.Comparable<Point2D>

Parameters:

that - the other point

Returns:

the value 0 if this string is equal to the argument string (precisely when equals() returns 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

polarOrder

public java.util.Comparator<Point2D> polarOrder()

Compares two points by polar angle (between 0 and 2π) with respect to this point.

Returns:

the comparator

atan2Order

public java.util.Comparator<Point2D> atan2Order()

Compares two points by atan2() angle (between –π and π) with respect to this point.

Returns:

the comparator

distanceToOrder

public java.util.Comparator<Point2D> distanceToOrder()

Compares two points by distance to this point.

Returns:

the comparator

equals

public boolean equals(java.lang.Object other)

Compares this point to the specified point.

Overrides:

equals in class java.lang.Object

Parameters:

other - the other point

Returns:

true if this point equals other; false otherwise

toString

public java.lang.String toString()

Return a string representation of this point.

Overrides:

toString in class java.lang.Object

Returns:

a string representation of this point in the format (x, y)

hashCode

public int hashCode()

Returns an integer hash code for this point.

Overrides:

hashCode in class java.lang.Object

Returns:

an integer hash code for this point

draw

public void draw()

Plot this point using standard draw.

drawTo

public void drawTo(Point2D that)

Plot a line from this point to that point using standard draw.

Parameters:

that - the other point

main

public static void main(java.lang.String[] args)

Unit tests the point data type.

Parameters:

args - the command-line arguments