source: trunk/EventBenchCore/src/de/ugoe/cs/eventbench/models/IncompleteMemory.java @ 253

package de.ugoe.cs.eventbench.models;

import java.security.InvalidParameterException;
import java.util.LinkedList;
import java.util.List;

/**
 * <p>
 * Implements a round-trip buffered memory of a specified length that can be
 * used to remember the recent history. Every event that happend longer ago than
 * the length of the memory is forgotten, hence the memory is incomplete.
 * </p>
 * 
 * @author Steffen Herbold
 * @version 1.0
 * 
 * @param <T>
 *            Type which is memorized.
 */
public class IncompleteMemory<T> implements IMemory<T> {

        /**
         * <p>
         * Maximum length of the memory.
         * </p>
         */
        private int length;

        /**
         * <p>
         * Internal storage of the history.
         * </p>
         */
        private List<T> history;

        /**
         * <p>
         * Constructor. Creates a new IncompleteMemory.
         * </p>
         * 
         * @param length
         *            number of recent events that are remembered
         * @throws InvalidParameterException
         *             This exception is thrown if the length is smaller than 1
         */
        public IncompleteMemory(int length) {
                if (length < 1) {
                        throw new InvalidParameterException(
                                        "Length of IncompleteMemory must be at least 1.");
                }
                this.length = length;
                history = new LinkedList<T>();
        }

        /*
         * (non-Javadoc)
         * 
         * @see de.ugoe.cs.eventbench.models.IMemory#add(java.lang.Object)
         */
        @Override
        public void add(T state) {
                if (history.size() == length) {
                        history.remove(0);
                }
                history.add(state);
        }

        /*
         * (non-Javadoc)
         * 
         * @see de.ugoe.cs.eventbench.models.IMemory#getLast(int)
         */
        @Override
        public List<T> getLast(int num) {
                if( num<1 ) {
                        return new LinkedList<T>();
                } else {
                return new LinkedList<T>(history.subList(
                                Math.max(0, history.size() - num),
                                history.size())); // defensive copy
                }
        }

        /**
         * <p>
         * Returns the current length of the memory. This can be less than
         * {@link #length}, if the overall history is less than {@link #length}.
         * </p>
         * 
         * @return length of the current memory
         */
        public int getLength() {
                return history.size();
        }
}