Simulation of airport/supermarket carts organization system behaviour.

Chain.java

public class Chain{

	private List<Cart> carts = new ArrayList<Cart>();
	
	private void attach(Cart c)
	{
		if(getSize() >= 2) // If chain has no more than 2 carts , then leave both carts edge field set to true
		{
			getLastCart().setEdge(false);
		}
		carts.add(c);
		getLastCart().setEdge(true);
	}
	
	public void attachEnd(int n)
	{
		for(int i = 0 ; i < n; i++)
		{
			if(getSize() >=2)
			{
				getLastCart().setEdge(false);
			}
			carts.add(new Cart());
			getLastCart().setEdge(true);
		}
	}
	
	public void attachStart(int n)
	{
		for(int i = 0 ; i < n; i++)
		{
			if(getSize() >= 2)
			{
				getFirstCart().setEdge(false);
			}
			carts.add(0 ,new Cart());
			getFirstCart().setEdge(true);
		}
	}
	
	private Cart getFirstCart()
	{
		if(carts.isEmpty())
		{
			throw new EmptyChainException();
		}
		else
		{
			return carts.get(0);
		}
	} 
	
	private Cart getLastCart()
	{
		if(carts.isEmpty())
		{
			throw new EmptyChainException();
		}
		else
		{
			return carts.get(carts.size()-1);
		}
	}
	
	public int getSize()
	{
		return carts.size();
	}
	
	public void removeFirst()
	{
		if(carts.isEmpty())
		{
			throw new EmptyChainException();
		}
		else
		{
			getFirstCart().setEdge(false);
			carts.remove(0);
			getFirstCart().setEdge(true);
		}	
	}
	
	public void removeLast()
	{
		if(carts.isEmpty())
		{
			throw new EmptyChainException();
		}
		else
		{
			getLastCart().setEdge(false);
			carts.remove(carts.size()-1);
			getLastCart().setEdge(true);
		}	
	}
	
	public void removeEdges()
	{
		if(carts.isEmpty())
		{
			throw new EmptyChainException();
		}
		else if(carts.size() == 1)
		{
			throw new MonoCartChainException();
		}
		else
		{
			getFirstCart().setEdge(false);
			getLastCart().setEdge(false);
			carts.remove(0);
			carts.remove(carts.size()-1);
			getFirstCart().setEdge(true);
			getLastCart().setEdge(true);
		}
	}
	
	public List<Chain> slice(int slices)
	{
		if(carts.isEmpty())
		{
			throw new EmptyChainException();
		}
		
		if(slices == 1 || slices == 0)
		{
			List<Chain> lc = new ArrayList<Chain>();
			lc.add(this);
			return lc;
		}
		
		int begin = 0;
		int step  = carts.size()/slices;
		int diff  = carts.size() - (step*slices); //The remainder of the division. If diff > 0 then the FIRST Chain will contain the remainders carts
		int end   = step+diff; 
		
		List<Chain> lc = new ArrayList<Chain>();
		
		for(int i = 0 ; i < slices; i++)
		{
			lc.add(new Chain());
		}
		
		for(int i = 0 ; i < slices; i++)
		{
			for(; begin < end; begin++)
			{
				lc.get(i).attach(carts.get(begin));
			}
			end+=step;
		}	
		return lc;
	}
	
	private class Cart
	{
		private boolean edge;

		public boolean isEdge() 
		{
			return edge;
		}

		public void setEdge(boolean edge) 
		{
			this.edge = edge;
		}
	}
	
}

EmptyChainException.java

class EmptyChainException extends RuntimeException{
	
	private static final long serialVersionUID = 1L;	
	private static final String msg = "Chain is empty.";
	
	EmptyChainException()
	{
		super(msg);
	}	
}

MonoCartChainException.java

class MonoCartChainException extends RuntimeException{

	private static final long serialVersionUID = 2L;
	private static final String msg = "Chain contains only one Cart.";
	
	public MonoCartChainException()
	{
		super(msg);
	}
}