BrainfuckInterpreter.java

package org.alternadev.brainfuck;

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.nio.charset.Charset;

public class BrainfuckInterpreter {

  private int pointer;
	private byte[] cells;
	private OutputStream outStream;
	private InputStream inStream;
	private char[] chars;
	private int currChar;

	public BrainfuckInterpreter(int cellAmount, OutputStream outStream,
			InputStream inStream) {
		cells = new byte[cellAmount];
		this.outStream = outStream;
		this.inStream = inStream;
	}

	public void interpret(String s) throws Exception {
		chars = s.toCharArray();
		for (; currChar < chars.length; currChar++)
			interpretChar(chars[currChar]);
	}

	private void interpretChar(char c) throws Exception {
		switch (c) {
		case Token.INC_PTR:
			pointer++;

			break;
		case Token.DEC_PTR:
			pointer--;

			break;
		case Token.INC_CELL:
			cells[pointer]++;

			break;
		case Token.DEC_CELL:
			cells[pointer]--;

			break;
		case Token.PUT:
			outStream.write((char) cells[pointer]);
			outStream.flush();
			break;
		case Token.GET:
			cells[pointer] = (byte) inStream.read();
			break;
		case Token.BRACKET_LEFT:
			if (cells[pointer] == 0) {
				int i = 1;
				while (i > 0) {
					char c2 = chars[++currChar];
					if (c2 == Token.BRACKET_LEFT)
						i++;
					else if (c2 == Token.BRACKET_RIGHT)
						i--;
				}
			}
			break;
		case Token.BRACKET_RIGHT:
			int i = 1;
			while (i > 0) {
				char c2 = chars[--currChar];
				if (c2 == Token.BRACKET_LEFT)
					i--;
				else if (c2 == Token.BRACKET_RIGHT)
					i++;
			}
			currChar--;
			break;

		}

	}

	class Token {
		public static final char INC_PTR = '>';
		public static final char DEC_PTR = '<';
		public static final char INC_CELL = '+';
		public static final char DEC_CELL = '-';
		public static final char PUT = '.';
		public static final char GET = ',';
		public static final char BRACKET_LEFT = '[';
		public static final char BRACKET_RIGHT = ']';
	}

	public static void main(String[] rolfi) throws Exception {
		BrainfuckInterpreter inter = new BrainfuckInterpreter(100, System.out,
				System.in);
		if (rolfi.length == 0)
			System.err.println("Please give me a File as Parameter!");
		else
			inter.interpret(readFile(rolfi[0]));
	}

	private static String readFile(String path) throws IOException {
		FileInputStream stream = new FileInputStream(new File(path));
		try {
			FileChannel fc = stream.getChannel();
			MappedByteBuffer bb = fc.map(FileChannel.MapMode.READ_ONLY, 0,
					fc.size());
			return Charset.defaultCharset().decode(bb).toString();
		} finally {
			stream.close();
		}
	}
}