net.sf.javagimmicks.collections.LinkedRing Maven / Gradle / Ivy

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package net.sf.javagimmicks.collections;

import java.util.NoSuchElementException;


public class LinkedRing extends AbstractRing
{
    private int _size = 0;
    private RingElement _hook = null;
    
    public int size()
    {
        return _size;
    }
    
    public RingCursor cursor()
    {
        return new LinkedRingCursor(this, _hook);
    }

    private static class RingElement
    {
        private RingElement _previous;
        private RingElement _next;
        
        private E _value;
    }
    
    private static class LinkedRingCursor extends BasicRingCursor>
    {
        private RingElement _current;
        
        private LinkedRingCursor(LinkedRing ring, RingElement current)
        {
            super(ring);
            _current = current;
        }
        
        public E get()
        {
            if(_current == null)
            {
                throw new NoSuchElementException("Ring is empty");
            }
            
            return _current._value;
        }
        
        public void insertAfter(E value)
		{
        	RingElement next = _current != null ? _current._next : null;
        	
        	insert(value, _current, next);
		}

		public void insertBefore(E value)
        {
        	RingElement previous = _current != null ? _current._previous : null;
        	
        	insert(value, previous, _current);
        }

        public E next()
        {
        	checkForModification();
        	
            if(_current == null)
            {
                throw new NoSuchElementException("Ring is empty");
            }
            
            _current = _current._next;
            
            return get();
        }

        public E previous()
        {
        	checkForModification();

            if(_current == null)
            {
                throw new NoSuchElementException("Ring is empty");
            }

            _current = _current._previous;
            
            return get();
        }

        public E remove()
        {
        	checkForModification();
        	
        	// Get the ring size
        	int ringSize = _ring._size;
        	
        	// If nothing to remove, throw an exception
        	if(ringSize == 0)
        	{
        		throw new NoSuchElementException();
        	}

        	E result = _current._value;
        	
        	if(ringSize == 1)
        	{
            	// If only one element is remaining, clean up everything
        		_current._next = null;
        		_current._previous = null;
        		_current = null;
        		_ring._hook = null;
        	}
        	else
        	{
                // Get the next and previous element
                RingElement nextElement = _current._next;
                RingElement previousElement = _current._previous;
                
                // Re-assign their links
                nextElement._previous = previousElement;
                previousElement._next = nextElement;
                
                // Clean links of element to remove
                _current._next = null;
                _current._previous = null;
                
                // Relink the hook (if necessary) and the current RingCursor position
                if(_ring._hook == _current)
                {
                    _ring._hook = nextElement;
                }
                _current = nextElement;
        	}

        	// Decrease ring size
        	--_ring._size;
        	
        	// Update modification counters
            ++_ring._modCount;
            ++_expectedModCount;
            
            return result;
        }
        
        public RingCursor cursor()
        {
            return new LinkedRingCursor(_ring, _current);
        }

        private void insert(E value, RingElement previous, RingElement next)
        {
        	checkForModification();
        	
            // Create the new element and set it's value
        	RingElement newElement = new RingElement();
        	newElement._value = value;

        	if(previous == null  || next == null)
        	{
        		// This is the first element, so link it to itself
            	newElement._previous = newElement;
            	newElement._next = newElement;
            	
            	// Also update the current element and the hook of the ring
            	_current = newElement;
            	_ring._hook = newElement;
        	}
            else
            {
            	// Set links of new element
            	newElement._previous = previous;
            	newElement._next = next;

                // Set links to new element
            	previous._next = newElement;
            	next._previous = newElement;
            }
        	
        	// Increase ring size
            ++_ring._size;
            
            // Update modification counters
            ++_ring._modCount;
            ++_expectedModCount;
        }
    }
}