package  net.acid.utils;

 import  java.util.ArrayList;
 import  java.util.List;
 import  java.util.Stack;

 public   class  PortList {

	 public  PortList( int  portCount) {
		list =  new  ArrayList(portCount);
		freePorts =  new  Stack();
		count = portCount;
	}
	
	 public   int  size() {
		 return  count;
	}

	 public   boolean  add(Object obj) {
		 if  (freePortNumber > - 1 ) {
			list.add(freePortNumber, obj);
			freePortNumber = (list.size() < count) ? freePortNumber++ : - 1 ;
			 if  (freePortNumber == - 1  && !freePorts.isEmpty()) { 
				freePortNumber = ( (Integer) freePorts.pop() ).intValue();
			}
			 return  true;
		}
		 return  false;
	}

	 public  Object remove( int  index) {
		Object obj = list.remove(index);
		freePorts.push( new  Integer(index));
		 if  (freePortNumber == - 1 )
			freePortNumber = index;
		 return  obj;
	}

        ...

	 private   int  freePortNumber =  0 ;
	 private   int  count;
	 private  List list;
	 private  Stack freePorts;
}