Hex Converter

import java.io.File;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;


public class Converter {
    private static final String[] INSTRUCTIONS = {
        "LDA",      // Address
        "STA",      // Address
        "MOV A,B",
        "MOV B,A",
        "MOV A",    // Immediate
        "IN",
        "OUT",
        "ADD B",
        "ADC B",
        "SUB B",
        "SBB B",
        "ADC",      // Immediate
        "SBB",      // Address
        "CMP B",
        "DEC",
        "JZ",       // Address
        "JG",       // Address
        "PUSH",
        "POP",
        "CALL",     // Address
        "RET",
        "JMP",      // Address
        "HLT",
        "NOP",
        "RCL",
        "RCR",
        "AND",      // Immediate
        "OR B"
    };


    private static final String INPUT_FILENAME = "input.txt";
    private static final String OPCODE_OUTPUT_FILENAME = "op.hex";
    private static final String DATA_OUTPUT_FILENAME = "data.hex";

    public static void main(String[] args) throws Exception {
        Scanner input = new Scanner(new File(INPUT_FILENAME));

        new File(DATA_OUTPUT_FILENAME).delete();
        new File(OPCODE_OUTPUT_FILENAME).delete();

        FileWriter opcodeWriter = new FileWriter(OPCODE_OUTPUT_FILENAME);
        FileWriter dataWriter = new FileWriter(DATA_OUTPUT_FILENAME);

        int address = 0;

        while(input.hasNextLine()) {
            String instruction = input.nextLine();
            for (int opcode = 0; opcode < INSTRUCTIONS.length; opcode++) {
                if (instruction.startsWith(INSTRUCTIONS[opcode])) {
                    int data = 0;

                    if (instruction.length() > INSTRUCTIONS[opcode].length()) {
                        String dataStr = instruction.substring(instruction.length() - 2);
                        data = Integer.parseInt(dataStr, 16);
                    }

                    writeData(opcode, address, opcodeWriter);
                    writeData(data, address, dataWriter);

                    address++;
                    break;
                }
            }
        }

        opcodeWriter.write(":00000001FF");
        dataWriter.write(":00000001FF");

        opcodeWriter.close();
        dataWriter.close();

        input.close();
    }

    public static void writeData(int data, int address, FileWriter writer) throws IOException {
        StringBuilder builder = new StringBuilder();
        builder.append(":01");
        String addressStr = "0000" + Integer.toHexString(address).toUpperCase();
        addressStr = addressStr.substring(addressStr.length() - 4);
        builder.append(addressStr);

        builder.append("00");

        String dataStr = "00" + Integer.toHexString(data).toUpperCase();
        dataStr = dataStr.substring(dataStr.length() - 2);
        builder.append(dataStr);

        int checkSum = (256 - 1 - address - data) % 256;
        String checksumStr = "00" + Integer.toHexString(checkSum);
        checksumStr = checksumStr.substring(checksumStr.length() - 2);
        builder.append(checksumStr);

        builder.append("\n");

        writer.append(builder.toString());
    }
}