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'databene commons' is an open source Java library by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.

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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.databene.commons.collection;

import java.util.*;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * Counts objects.
 * Created: 14.12.2006 18:03:47
 * @param  the type of the counted elements
 * @author Volker Bergmann
 */
public class ObjectCounter {
	
    private Map instances;
    long totalCount;

    public ObjectCounter(int initialCapacity) {
        instances = new HashMap(initialCapacity);
        totalCount = 0;
    }

    // interface -------------------------------------------------------------------------------------------------------

    public void count(E instance) {
        AtomicInteger counter = instances.get(instance);
        if (counter == null)
            instances.put(instance, new AtomicInteger(1));
        else
            counter.incrementAndGet();
        totalCount++;
    }

	public void uncount(String instance) {
        AtomicInteger counter = instances.get(instance);
        if (counter == null)
            throw new IllegalStateException("Cannot uncount: " + instance);
        counter.decrementAndGet();
        totalCount--;
	}

    public Set objectSet() {
        return instances.keySet();
    }

    public int getCount(E instance) {
        AtomicInteger counter = instances.get(instance);
        return (counter != null ? counter.intValue() : 0);
    }

    public double getRelativeCount(E instance) {
        return (double) getCount(instance) / totalCount;
    }

    public double averageCount() {
        return totalCount / instances.size();
    }

    public double totalCount() {
	    return totalCount;
    }
    
    public Map getCounts() {
    	return instances;
    }

    public boolean equalDistribution(double tolerance) {
        double average = averageCount();
        Collection counts = instances.values();
        for (AtomicInteger count : counts) {
            if (Math.abs((count.doubleValue() - average) / average) > tolerance)
                return false;
        }
        return true;
    }

    @Override
    public String toString() {
        StringBuilder buffer = new StringBuilder("[");
        Iterator> iterator = instances.entrySet().iterator();
        if (iterator.hasNext()) {
            Map.Entry entry = iterator.next();
            buffer.append(entry.getKey()).append(':').append(entry.getValue());
        }
        while (iterator.hasNext()) {
            Map.Entry entry = iterator.next();
            buffer.append(", ").append(entry.getKey()).append(':').append(entry.getValue());
        }
        buffer.append(']');
        return buffer.toString();
    }

}