//Elevator 
// This models an simple elevator.  The elevator goes up, stopping at all
// requested floors in the direction that it is going.  When it reaches the
// limit of its direction (top floor for UP and bottom floor for DOWN), it
// changes direction.

class Elevator

    //members
    public final boolean  UP = true
    public final boolean DOWN = false
    public final boolean ON = true
    public final boolean OFF = false
    public final boolean OPEN = true
    public final boolean CLOSED = false

    private boolean direction      
    private int currentFloor
    private boolean doorStatus
    private boolean[] floorButtonInElevator
    private boolean emergencyStopButton
    private boolean operative
    private boolean returnToGround
    private double capacityWt
    private double currentWt
    private int MaximumFloorNumber,MinimumFloorNumber


//constructor
PRECONDITION:	none
INPUT:		two ints, min floor and maximum floor
PROCESS:	It assigns MinimumFloorNumber to minimum floor and 
		MaximumFloorNumber to maximum floor.  It creates the array of 
		size MaximumFloorNumber-MinimumFloorNumber+1 for 
		floorButtonInElevator.  It sets all of the floor buttons in the
		three arrays to be OFF.  It sets doorStatus to be OPEN,
		emergencyStopButton to be OFF, direction to be UP, operative to
		be ON, returnToGround to be OFF, the currentFloor to be
		zero, the ground floor, and the currentWt to be zero.
OUTPUT:		none
POSTCONDITION:  The array floorButtonInElevator is created and initialized. The
		doorStatus, direction, emergencyStopButton, operative,
		returnToGround, and currentFloor are initialized.


    //query methods

getCurrentFloor
PRECONDITION: 	none
INPUT:		none
PROCESS:	returns the currentFloor
OUTPUT:		int, the currentFloor
POSTCONDITION:	none

getDoorStatus
PRECONDITION:	none
INPUT:		none
PROCESS:	returns the doorStatus
OUTPUT:		boolean, the doorstatus
POSTCONDITION:	none

getEmergencyStopButton
PRECONDITION:	none
INPUT:		none
PROCESS:	returns the emergencyStopButton status
OUTPUT:		boolean, the emergencyStopButton
POSTCONDITION:	none

getDirection
PRECONDITION: 	none
INPUT:		none
PROCESS:	returns the direction
OUTPUT:		boolean, the direction
POSTCONDITION:	none

getOperative  
PRECONDITION:	none
INPUT:		none
PROCESS:	returns the operative status
OUTPUT:		boolean, the operative
POSTCONDITION:	none

getCurrentWt
PRECONDITON: 	none
INPUT:		none
PROCESS:	returns the currentWt
OUTPUT:		double, the currentWt
POSTCONDITION:  none

getReturnToGround  
PRECONDITION:	none
INPUT:		none
PROCESS:	returns the returnToGround status
OUTPUT:		boolean, the returnToGround
POSTCONDITION:	none


    //update methods
changeFloor
PRECONDITION:	doorStatus is CLOSED, emergencyStopButton is OFF, operative is
		ON, and currentWt is less than capacityWt
INPUT:		none
PROCESS:	If elevator is at MaximumFloorNumber and direction is UP, it
		sets the direction to be DOWN, and sets all of the
		floorButtonInElevator to be OFF.  If the elevator is at the
		MinimumFloorNumber and the direction is DOWN, it sets the
		direction to be UP, and sets all of the floorButtonInElevator
		to be OFF.  Otherwise it changes the currentFloor by one in
		the direction it is going.  If the new currentFloor has the
		corresponding floorButtonInElevator ON, it opens the door and
		sets the corresponding button to be OFF.  If returnToGround is
		ON and the currentFloor is not the ground floor, it ignores all
		button requests and keeps the door closed.
OUTPUT:		none
POSTCONDITION:	direction, currentFloor, doorStatus, and floorButtonInElevator,
		could be modifed.	

openDoor
PRECONDITION:	elevator is operative 
INPUT:		none
PROCESS:	changes doorStatus to OPEN
OUTPUT:		none
POSTCONDITION:	doorStatus is OPEN

closeDoor
PRECONDITION:	elevator is operative and currentWt is less than capacityWt 
INPUT:		none
PROCESS:	changes doorStatus to CLOSED
OUTPUT:		none
POSTCONDITION:	doorStatus is CLOSED

setFloorButton
PRECONDITION:	floorDesired is not more than MaximumFloorNumber and not less
		than MinimumFloorNumber.
INPUT:		int, floorDesired 
PROCESS: 	It sets the index of floorInElevator to be ON.
OUTPUT:		none
POSTCONDITION:	One of the indices of floorInElevator is set to ON.

setEmergencyStopButton
PRECONDITION:	none
INPUT:		boolean, the new status
PROCESS:	emergencyStopButton is set to the new status.
OUTPUT:		none
POSTCONDITION:	emergencyStopButton is modified.

haltElevator
PRECONDITION:	none
INPUT:		none
PROCESS:	operative is set to OFF.
OUTPUT:		none
POSTCONDITION:	operative is OFF.

setOperative
PRECONDITION:	none
INPUT:		boolean, the new status
PROCESS:	operative is set to the new status
OUTPUT:		none
POSTCONDITION:	operative is modified.

returnToGroundFloor
PRECONDITION:	elevator is operative
INPUT:		none
PROCESS:	It sets returnToGround to be ON, and sets direction to be DOWN.
OUTPUT:		none
POSTCONDITION:	returnToGround and direction have been modified.

enterElevator
PRECONDITON:    door is open and inputWt + currentWt is less than capacityWt
INPUT:	        double, inputWt
PROCESS:       	It adds the inputWt to the currentWt
OUTPUT:		none
POSTCONDITION:	the currentWt is modified

exitElevator
PRECONDITON:	door is open
INPUT:		none
PROCESS:	the currentWt is decreased by the exitWt
OUTPUT:		double, the exitWt
POSTCONDITION:  the currentWt is modified