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/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.apache.commons.math.stat.descriptive;

import java.io.Serializable;

/**
 * Abstract base class for all implementations of the 
 * {@link UnivariateStatistic} interface.
 * 
 * Provides a default implementation of evaluate(double[]), 
 * delegating to evaluate(double[], int, int) in the natural way.
 * 
 * 
 * Also includes a test method that performs generic parameter
 * validation for the evaluate methods.
 * 
 * @version $Revision: 617953 $ $Date: 2008-02-02 22:54:00 -0700 (Sat, 02 Feb 2008) $
 */
public abstract class AbstractUnivariateStatistic
    implements UnivariateStatistic, Serializable {
    
    /** Serialization UID */
    private static final long serialVersionUID = -8007759382851708045L;

    /**
     * @see org.apache.commons.math.stat.descriptive.UnivariateStatistic#evaluate(double[])
     */
    public double evaluate(final double[] values) {
        test(values, 0, 0);
        return evaluate(values, 0, values.length);
    }

    /**
     * @see org.apache.commons.math.stat.descriptive.UnivariateStatistic#evaluate(double[], int, int)
     */
    public abstract double evaluate(final double[] values, final int begin, final int length);

    /**
     * This method is used by evaluate(double[], int, int) methods
     * to verify that the input parameters designate a subarray of positive length.
     * 
     * 

     * returns true iff the parameters designate a subarray of 
     * positive length
     * throws IllegalArgumentException if the array is null or
     * or the indices are invalid
     * returns false
 if the array is non-null, but 
     * length is 0.
     * 

     *
     * @param values the input array
     * @param begin index of the first array element to include
     * @param length the number of elements to include
     * @return true if the parameters are valid and designate a subarray of positive length
     * @throws IllegalArgumentException if the indices are invalid or the array is null
     */
    protected boolean test(
        final double[] values,
        final int begin,
        final int length) {

        if (values == null) {
            throw new IllegalArgumentException("input value array is null");
        }
        
        if (begin < 0) {
            throw new IllegalArgumentException("start position cannot be negative");
        }
        
        if (length < 0) {
            throw new IllegalArgumentException("length cannot be negative");
        }
        
        if (begin + length > values.length) {
            throw new IllegalArgumentException(
                "begin + length > values.length");
        }

        if (length == 0) {
            return false;
        }

        return true;

    }
}