Java All Items

import java.io.*;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.ArrayList;
import java.util.List;

public class ItemSet
{
    private final static String MAPPING_FILE_NAME = "idmap.txt";
    private final static List<Integer> item_offsets = new ArrayList<>();
    private final static List<Integer> item_ids = new ArrayList<>();
    private final static List<String> item_names = new ArrayList<>();

    private static int byte_to_uint(byte b)
    {
        return (int) (b) & 0xFF;
    }

    private static int byte_to_uint16_le(byte[] ref, int offset)
    {
        if (ref.length < offset + 2)
            throw new RuntimeException("Buffer overflowed - Offset " + offset);
        return byte_to_uint(ref[offset]) | (byte_to_uint(ref[offset + 1]) << 8);
    }

    private static void write_uint16_le(byte[] ref, int offset, int val)
    {
        if (ref.length < offset + 2)
            throw new RuntimeException("Buffer overflowed - Offset " + offset);
        ref[offset] = (byte) (val % 256);
        ref[offset + 1] = (byte) (val / 256);
    }

    private static void read_mapping() throws IOException
    {
        final BufferedReader in = new BufferedReader(new InputStreamReader(new FileInputStream(MAPPING_FILE_NAME), "UTF-16"));
        String line = null;
        int line_num = 0;
        while((line = in.readLine()) != null)
        {
            line_num++;
            final String[] each_line = line.split("\\t");
            if(each_line.length != 3)
            {
                throw new RuntimeException("Mapping file line #" + line_num + " \"" + line + "\" is corrupted.\n");
            }
            item_offsets.add(Integer.parseInt(each_line[0], 16));
            item_ids.add(Integer.parseInt(each_line[1], 16));
            item_names.add(each_line[2]);
        }
        in.close();
    }

    public static void main(String[] args) throws IOException
    {
        if (args.length == 1)
        {
            read_mapping();
            System.out.print("Read mapping file \"" + MAPPING_FILE_NAME + "\". Records: "+ item_offsets.size() + ".\n");
            final byte[] buffer;
            final Path path = Paths.get(args[0]);
            final Path output = Paths.get(args[0] + ".hacked");

            buffer = Files.readAllBytes(path);
            System.out.print("Read save file \"" + args[0] + "\". Size: " + buffer.length + " bytes.\n");
            for(int i = 0; i < item_offsets.size(); i++)
            {
                write_uint16_le(buffer, item_offsets.get(i), item_ids.get(i));
                write_uint16_le(buffer, item_offsets.get(i) + 2, 999);
                System.out.print("Giving 999 " + item_names.get(i) + ". ID: 0x" +
                        Integer.toHexString(item_ids.get(i)) +
                        " Offset: 0x" + Integer.toHexString(item_offsets.get(i)) + "\n");
            }
            Files.write(output, buffer);
            System.out.print("Completed.\n");
        } else
        {
            System.err.println("Incorret arguments.");
        }
    }
}