001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.math.util;
018    
019    
020    /**
021     * Provides a standard interface for double arrays.  Allows different
022     * array implementations to support various storage mechanisms
023     * such as automatic expansion, contraction, and array "rolling".
024     *
025     * @version $Revision: 811685 $ $Date: 2009-09-05 13:36:48 -0400 (Sat, 05 Sep 2009) $
026     */
027    public interface DoubleArray {
028    
029        /**
030         * Returns the number of elements currently in the array.  Please note
031         * that this may be different from the length of the internal storage array.
032         *
033         * @return number of elements
034         */
035        int getNumElements();
036    
037        /**
038         * Returns the element at the specified index.  Note that if an
039         * out of bounds index is supplied a ArrayIndexOutOfBoundsException
040         * will be thrown.
041         *
042         * @param index index to fetch a value from
043         * @return value stored at the specified index
044         * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
045         *         zero or is greater than <code>getNumElements() - 1</code>.
046         */
047        double getElement(int index);
048    
049        /**
050         * Sets the element at the specified index.  If the specified index is greater than
051         * <code>getNumElements() - 1</code>, the <code>numElements</code> property
052         * is increased to <code>index +1</code> and additional storage is allocated
053         * (if necessary) for the new element and all  (uninitialized) elements
054         * between the new element and the previous end of the array).
055         *
056         * @param index index to store a value in
057         * @param value value to store at the specified index
058         * @throws ArrayIndexOutOfBoundsException if <code>index</code> is less than
059         *         zero.
060         */
061        void setElement(int index, double value);
062    
063        /**
064         * Adds an element to the end of this expandable array
065         *
066         * @param value to be added to end of array
067         */
068        void addElement(double value);
069    
070        /**
071         * <p>
072         * Adds an element to the end of the array and removes the first
073         * element in the array.  Returns the discarded first element.
074         * The effect is similar to a push operation in a FIFO queue.
075         * </p>
076         * <p>
077         * Example: If the array contains the elements 1, 2, 3, 4 (in that order)
078         * and addElementRolling(5) is invoked, the result is an array containing
079         * the entries 2, 3, 4, 5 and the value returned is 1.
080         * </p>
081         *
082         * @param value the value to be added to the array
083         * @return the value which has been discarded or "pushed" out of the array
084         *         by this rolling insert
085         */
086        double addElementRolling(double value);
087    
088        /**
089         * Returns a double[] array containing the elements of this
090         * <code>DoubleArray</code>.  If the underlying implementation is
091         * array-based, this method should always return a copy, rather than a
092         * reference to the underlying array so that changes made to the returned
093         *  array have no effect on the <code>DoubleArray.</code>
094         *
095         * @return all elements added to the array
096         */
097        double[] getElements();
098    
099        /**
100         * Clear the double array
101         */
102        void clear();
103    
104    }