mapcache.java

A static analysis tool to find bugs in Java programs

/*
 * FindBugs - Find Bugs in Java programs
 * Copyright (C) 2005, University of Maryland
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

package edu.umd.cs.findbugs.util;

import java.util.LinkedHashMap;
import java.util.Map;

import org.apache.bcel.classfile.JavaClass;

/**
 * Provide a HashMap that can only grow to a specified maximum capacity,
 * with entries discarded using a LRU policy to keep the size of the HashMap
 * within that bound. 
 * 
 * @author pugh
 */
public class MapCache<K,V> extends LinkedHashMap<K,V> {
	private static final long serialVersionUID = 0L;
	int maxCapacity;
	/**
	 * Create a new MapCache
	 * @param maxCapacity - maximum number of entries in the map
	 */
	public MapCache(int maxCapacity) {
		super(16, 0.75f, true);
		this.maxCapacity = maxCapacity;
		count = new int[maxCapacity];
	}
	int [] count;
	@Override
	public V get(Object k) { 
		if (false) {
		int age = count.length-1;
		for(Map.Entry<K,V> e : entrySet()) {
			if (e.getKey().equals(k)) {
				count[age]++;
				if (false && age > 20 && k instanceof JavaClass) {

					System.out.println("Reusing value from " + age + " steps ago ");
					System.out.println("Class " + ((JavaClass)k).getClassName());
					new RuntimeException().printStackTrace(System.out);
				}
				break;
			}
			age--;

		}
		}
		return super.get(k);
	}
	@Override
	protected boolean removeEldestEntry(Map.Entry<K,V> eldest) {
		boolean result = size() > maxCapacity;
		if (false && result && eldest.getKey() instanceof JavaClass)
				System.out.println("Dropping " + ((JavaClass)eldest.getKey()).getClassName());
		return result;
	 }

	public String getStatistics() {
		StringBuffer b = new StringBuffer();
		for(int c : count) 
			b.append(c).append(" ");
		return b.toString();
	}

}