SparseList.java #1

package journal.tools;

import java.util.AbstractList;
import java.util.List;
import java.util.Map;
import java.util.HashMap;

public class SparseList<E> extends AbstractList<E> implements List<E> 
{
	private Map<Integer, E> backing = new HashMap<Integer, E>();
	private int size = 0;
	private final E defaultValue;
	
	public SparseList(E defaultValue) {
		this.defaultValue = defaultValue;
	}
	
	private void checkSize(int index) {
		if( index > size ) {
			size = index + 1;
		}
	}
	
	private E returnValue(E result) {
		return result == null ? defaultValue : result;
	}
	
	@Override
	public E get(int arg) {
		E result = backing.get(arg);
		return returnValue(result);
	}

	@Override
	public int size() {
		return size;
	}

	@Override
	public E set(int index, E element) {
		checkSize( index );
		if( element == defaultValue ) {
			E result = backing.remove(index);
			return returnValue(result);
		}
		if( element == null ) throw new NullPointerException();
		E result = backing.put( index, element );
		return returnValue(result);
	}
		
	@Override
	public E remove(int index) {
		throw new UnsupportedOperationException("Not yet implemented");
	}
	
	public static void main(String args[]) {
		SparseList<Integer> list = new SparseList<Integer>(0);
		list.set(1, 1);
		list.set(5, 5);
		list.set(17, 1);
		
		list.set(17, list.get(17) + 1);
		list.set(19, list.get(19) + 1);
		
		for( int index = 0; index < list.size(); index++ ) {
			System.out.println("" + index + " : " + list.get(index));
		}
	}
}