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Java example source code file (MnistDbFile.java)

This example Java source code file (MnistDbFile.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

ioexception, mnistdbfile, randomaccessfile, runtimeexception, string, this

The MnistDbFile.java Java example source code

/*
 *
 *  * Copyright 2015 Skymind,Inc.
 *  *
 *  *    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.deeplearning4j.datasets.mnist;


import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;

/**
 * MNIST database file containing entries that can represent image or label
 * data. Extends the standard random access file with methods for navigating
 * over the entries. The file format is basically idx with specific header
 * information. This includes a magic number for determining the type of stored
 * entries, count of entries.
 */
public abstract class MnistDbFile extends RandomAccessFile {
    private int count;
    

    /**
     * Creates new instance and reads the header information.
     * 
     * @param name
     *            the system-dependent filename
     * @param mode
     *            the access mode
     * @throws IOException
     * @throws FileNotFoundException
     * @see RandomAccessFile
     */
    public MnistDbFile(String name, String mode) throws IOException {
        super(name, mode);
        if (getMagicNumber() != readInt()) {
            throw new RuntimeException("This MNIST DB file " + name + " should start with the number " + getMagicNumber() + ".");
        }
        count = readInt();
    }

    /**
     * MNIST DB files start with unique integer number.
     * 
     * @return integer number that should be found in the beginning of the file.
     */
    protected abstract int getMagicNumber();

    /**
     * The current entry index.
     * 
     * @return long
     * @throws IOException
     */
    public long getCurrentIndex() throws IOException {
        return (getFilePointer() - getHeaderSize()) / getEntryLength() + 1;
    }

    /**
     * Set the required current entry index.
     * 
     * @param curr
     *            the entry index
     */
    public void setCurrentIndex(long curr) {
        try {
            if (curr < 0 || curr > count) {
                throw new RuntimeException(curr + " is not in the range 0 to " + count);
            }
            seek(getHeaderSize() + curr * getEntryLength());
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    public int getHeaderSize() {
        return 8; // two integers
    }

    /**
     * Number of bytes for each entry.
     * Defaults to 1.
     * 
     * @return int
     */
    public int getEntryLength() {
        return 1;
    }

    /**
     * Move to the next entry.
     * 
     * @throws IOException
     */
    public void next() throws IOException {
        if (getCurrentIndex() < count) {
            skipBytes(getEntryLength());
        }
    }

    /**
     * Move to the previous entry.
     * 
     * @throws IOException
     */
    public void prev() throws IOException {
        if (getCurrentIndex() > 0) {
            seek(getFilePointer() - getEntryLength());
        }
    }

    public int getCount() {
        return count;
    }
}

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