// File: TrafficLight.java from the package edu.colorado.simulations
// Additional documentation is available from the Throttle link in:
// http://www.cs.colorado.edu/~main/docs/
package edu.colorado.simulations;
/******************************************************************************
* A TrafficLight object simulates a simple traffic light.
*
* Java Source Code for this class:
*
* http://www.cs.colorado.edu/~main/edu/colorado/simulations/TrafficLight.java
*
*
* @author Michael Main
* (main@colorado.edu)
*
* @version
* Jan 12, 1999
******************************************************************************/
public class TrafficLight
{
private int redSpan; // Seconds that the light stays red
private int greenSpan; // Seconds that the light stays green
private boolean nowRed; // True if the light is now red
private int secondsUntilChange; // Seconds until the next color change
/**
* Construct a TrafficLight with a specified lengths of time
* that the light stays red and green.
* @param r
* the number of seconds that this light stays red
* @param g
* the number of seconds that this light stays green
* Precondition:
* Both r and g are positive.
* Postcondition:
* This TrafficLight has been initialized. It starts
* red and stays red for r seconds; then it switches to green for
* g seconds, back to red for r seconds, back to green for g
* seconds, and so on.
* @exception IllegalArgumentException
* Indicates that one of the parameters is zero or negative.
**/
public TrafficLight(int r, int g)
{
if (r <= 0)
throw new IllegalArgumentException("r <= 0: " + r);
if (g <= 0)
throw new IllegalArgumentException("g <= 0: " + g);
redSpan = r;
greenSpan = g;
nowRed = true;
secondsUntilChange = r;
}
/**
* Simulate the passage of a certain amount of time for this
* TrafficLight.
* @param t
* the number of seconds to simulate during the call to this method
* Precondition:
* t >= 0.
* Postcondition:
* This TrafficLight has simulated the passage of
* t more seconds of time.
* @exception IllegalArgumentException
* Indicates that t is negative.
**/
public void simulateTime(int t)
{
while (t >= secondsUntilChange)
{
t -= secondsUntilChange;
nowRed = !nowRed;
secondsUntilChange = nowRed ? redSpan : greenSpan;
}
secondsUntilChange -= t;
}
/**
* Check whether this TrafficLight is red.
* @param - none
* @return
* If this TrafficLight is red, then the return
* value is true; otherwise the return value is false.
**/
public boolean isRed( )
{
return nowRed;
}
/**
* Check whether this TrafficLight is green.
* @param - none
* @return
* If this TrafficLight is green, then the return
* value is true; otherwise the return value is false.
**/
public boolean isGreen( )
{
return !nowRed;
}
}