Package edu.princeton.cs.algs4

Class Particle

Object

edu.princeton.cs.algs4.Particle

public class Particle
extends Object

The Particle class represents a particle moving in the unit box, with a given position, velocity, radius, and mass. Methods are provided for moving the particle and for predicting and resolvling elastic collisions with vertical walls, horizontal walls, and other particles. This data type is mutable because the position and velocity change.

For additional documentation, see Section 6.1 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Constructor Summary

Constructors

Constructor	Description
Particle()	Initializes a particle with a random position and velocity.
Particle(double rx, double ry, double vx, double vy, double radius, double mass, Color color)	Initializes a particle with the specified position, velocity, radius, mass, and color.

Method Summary

Modifier and Type	Method	Description
void	bounceOff(Particle that)	Updates the velocities of this particle and the specified particle according to the laws of elastic collision.
void	bounceOffHorizontalWall()	Updates the velocity of this particle upon collision with a horizontal wall (by reflecting the velocity in the y-direction).
void	bounceOffVerticalWall()	Updates the velocity of this particle upon collision with a vertical wall (by reflecting the velocity in the x-direction).
int	count()	Returns the number of collisions involving this particle with vertical walls, horizontal walls, or other particles.
void	draw()	Draws this particle to standard draw.
double	kineticEnergy()	Returns the kinetic energy of this particle.
void	move(double dt)	Moves this particle in a straight line (based on its velocity) for the specified amount of time.
double	timeToHit(Particle that)	Returns the amount of time for this particle to collide with the specified particle, assuming no interening collisions.
double	timeToHitHorizontalWall()	Returns the amount of time for this particle to collide with a horizontal wall, assuming no interening collisions.
double	timeToHitVerticalWall()	Returns the amount of time for this particle to collide with a vertical wall, assuming no interening collisions.

Methods inherited from class java.lang.Object

clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Particle

public Particle(double rx,
                double ry,
                double vx,
                double vy,
                double radius,
                double mass,
                Color color)

Initializes a particle with the specified position, velocity, radius, mass, and color.

Parameters:

rx - x-coordinate of position

ry - y-coordinate of position

vx - x-coordinate of velocity

vy - y-coordinate of velocity

radius - the radius

mass - the mass

color - the color

Particle

public Particle()

Initializes a particle with a random position and velocity. The position is uniform in the unit box; the velocity in either direciton is chosen uniformly at random.

Method Detail

move

public void move(double dt)

Moves this particle in a straight line (based on its velocity) for the specified amount of time.

Parameters:

dt - the amount of time

draw

public void draw()

Draws this particle to standard draw.

count

public int count()

Returns the number of collisions involving this particle with vertical walls, horizontal walls, or other particles. This is equal to the number of calls to bounceOff(edu.princeton.cs.algs4.Particle), bounceOffVerticalWall(), and bounceOffHorizontalWall().

Returns:

the number of collisions involving this particle with vertical walls, horizontal walls, or other particles

timeToHit

public double timeToHit(Particle that)

Returns the amount of time for this particle to collide with the specified particle, assuming no interening collisions.

Parameters:

that - the other particle

Returns:

the amount of time for this particle to collide with the specified particle, assuming no interening collisions; Double.POSITIVE_INFINITY if the particles will not collide

timeToHitVerticalWall

public double timeToHitVerticalWall()

Returns the amount of time for this particle to collide with a vertical wall, assuming no interening collisions.

Returns:

the amount of time for this particle to collide with a vertical wall, assuming no interening collisions; Double.POSITIVE_INFINITY if the particle will not collide with a vertical wall

timeToHitHorizontalWall

public double timeToHitHorizontalWall()

Returns the amount of time for this particle to collide with a horizontal wall, assuming no interening collisions.

Returns:

the amount of time for this particle to collide with a horizontal wall, assuming no interening collisions; Double.POSITIVE_INFINITY if the particle will not collide with a horizontal wall

bounceOff

public void bounceOff(Particle that)

Updates the velocities of this particle and the specified particle according to the laws of elastic collision. Assumes that the particles are colliding at this instant.

Parameters:

that - the other particle

bounceOffVerticalWall

public void bounceOffVerticalWall()

Updates the velocity of this particle upon collision with a vertical wall (by reflecting the velocity in the x-direction). Assumes that the particle is colliding with a vertical wall at this instant.

bounceOffHorizontalWall

public void bounceOffHorizontalWall()

Updates the velocity of this particle upon collision with a horizontal wall (by reflecting the velocity in the y-direction). Assumes that the particle is colliding with a horizontal wall at this instant.

kineticEnergy

public double kineticEnergy()

Returns the kinetic energy of this particle. The kinetic energy is given by the formula 1/2 m v², where m is the mass of this particle and v is its velocity.

Returns:

the kinetic energy of this particle