public class Throttle {
	private int top;
	private int position;
	
	public Throttle(int size) {
		if (size <= 0)
			throw new IllegalArgumentException("Size <= 0: " + size);
		top = size;
	}
	
	public Throttle( )
	{
		top = 5;
		position = 0;
	}

	public double getFlow( )
	{
		return (double) position / (double) top;
	}

	public boolean isOn( )
	{
		return (position > 0);
	}
	
	public void shutOff( )
	{
		position = 0;
	}

	public void shift(int amount)
	{
		if (amount > top - position)
			position = top;
		else if (position + amount < 0)
			position = 0;
		else
			position += amount;
	}
}