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A fast and easy to use dense and sparse matrix linear algebra library written in Java.
There is a newer version: 0.43.1
/*
 * Copyright (c) 2020, Peter Abeles. All Rights Reserved.
 *
 * This file is part of Efficient Java Matrix Library (EJML).
 *
 * 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.ejml.data;

/**
 * A double array which can have its size changed
 *
 * @author Peter Abeles
 */
public class DGrowArray {
    public double[] data;
    public int length;

    public DGrowArray( int length ) {
        this.data = new double[length];
        this.length = length;
    }

    public DGrowArray() {
        this(0);
    }

    public int length() {
        return length;
    }

    public void reset() { reshape(0); }

    /**
     * Changes the array's length and doesn't attempt to preserve previous values if a new array is required
     *
     * @param length New array length
     */
    public DGrowArray reshape( int length ) {
        if (data.length < length) {
            data = new double[length];
        }
        this.length = length;
        return this;
    }

    /**
     * Increases the internal array's length by the specified amount. Previous values are preserved.
     * The length value is not modified since this does not change the 'meaning' of the array, just
     * increases the amount of data which can be stored in it.
     *
     * this.data = new data_type[ data.length + amount ]
     *
     * @param amount Number of elements added to the internal array's length
     */
    public void growInternal( int amount ) {
        double[] tmp = new double[data.length + amount];

        System.arraycopy(data, 0, tmp, 0, data.length);
        this.data = tmp;
    }

    public void setTo( DGrowArray original ) {
        reshape(original.length);
        System.arraycopy(original.data, 0, data, 0, original.length);
    }

    public void add( double value ) {
        if (length >= data.length) {
            growInternal(Math.min(500_000,data.length+10));
        }

        data[length++] = value;
    }

    public double get( int index ) {
        if (index < 0 || index >= length)
            throw new IllegalArgumentException("Out of bounds");
        return data[index];
    }

    public void set( int index, double value ) {
        if (index < 0 || index >= length)
            throw new IllegalArgumentException("Out of bounds");
        data[index] = value;
    }

    public void free() {
        data = new double[0];
        length = 0;
    }
}