Execute Brain****/Java

Execute Brain****/Java is an implementation of Brainf***. Other implementations of Brainf***.

Execute Brain****/Java is part of RCBF. You may find other members of RCBF at Category:RCBF.

In this implementation of Brainf***, the code is read in all at once and checked for uneven brackets (unequal amounts of [ and ] commands). If that error occurs, the code will obviously not be run.

Under the hood, the program memory is an ArrayList of Integers which expands only to the right. So, if the pointer moves past zero to the left, the program will exit and a "Pointer out of range" error message will be displayed. Due to the BufferedReader input class, return characters (ASCII 10 and 13) are ignored on input (the , command). Return characters are not ignored on output (the . command). More detailed information can be found in the comments scattered about the code.

import java.io.BufferedReader;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;

/**
 * Interprets Brainf**k source from std in or a file.
 * 
 * @author Mike Neurohr
 */
public class BF{
	private static int pointer;//memory pointer
	private static int codeIndex;//instruction number
	private static final int INITIAL_SIZE= 1000;//initial size of memory
	private static final String instChars= "[]<>,.+-";//valid code characters

	/**
	 * The main program. Holds the input loop and error-handling.
	 * 
	 * @param args 0: Source file others: ignored
	 */
	public static void main(String[] args){
		BufferedReader source;
		try{
			if(args.length == 0){//if no file specified
				source= new BufferedReader(new InputStreamReader(System.in));
			}else{
				source= new BufferedReader(new FileReader(args[0]));
			}
			char instruction;
			StringBuilder code= new StringBuilder();

			//counts for loop syntax errors
			int bCnt= 0;

			//read whole source in
			for(instruction= (char)source.read(); source.ready(); instruction=
					(char)source.read()){
				//remove extra characters
				if(instChars.contains(instruction + "")){
					//add the instruction to the clean code
					code.append(instruction);
					if(instruction == '[') bCnt++;
					if(instruction == ']') bCnt--;
				}
			}
			if(bCnt != 0){//if there is a bracket with no match
				System.err.println("Error: Uneven brackets.");
				return;
			}

			//set up input for ,
			BufferedReader input=
					new BufferedReader(new InputStreamReader(System.in));
			//set up memory
			ArrayList<Integer> memory= new ArrayList<Integer>(INITIAL_SIZE);
			memory.add(new Integer(0));
			
			pointer= 0; //initialize pointer
			//loop through the cleaned up code and execute
			for(codeIndex= 0;codeIndex < code.length();codeIndex++){
				instruction= code.charAt(codeIndex);
				switch(instruction){
				case '+':
					memory.set(pointer, memory.get(pointer) + 1);
					break;
				case '-':
					memory.set(pointer, memory.get(pointer) - 1);
					break;
				case '.':
					System.out.print((char)memory.get(pointer).intValue());
					//no errors possible here
					break;
				case ',':
					input(memory, input);
					//no errors possible here
					break;
				case '[':
					if(memory.get(pointer) == 0){
						//skip the code inside the loop
						jumpForward(code);
					}
					//if the loop can continue...
					//we don't need to check other things
					break;
				case ']':
					//go back to the corresponding [ to check
					jumpBack(code);
					break;
				case '>':
					pointer++;
					while(pointer + 1 > memory.size()) memory.add(0);
					break;
				case '<':
					if(pointer == 0){
						System.err.println("Pointer out of range (negative).");
						return;
					}
					pointer--;
					break;
				default:
				}
			}
		}catch(FileNotFoundException e){
			System.err.println("Error opening file.");
		}catch(IOException e){
			System.err.println("Error on input.");
		}
	}

	public static void jumpBack(StringBuilder code){
		//read back with pointer
		//count brackets until the corresponding [
		int bracketCnt= 1;
		while(codeIndex >= 0 && bracketCnt != 0){
			codeIndex--;
			char inst= code.charAt(codeIndex);
			if(inst == '[') bracketCnt--;
			if(inst == ']') bracketCnt++;
		}
		//"- 1" to offset the next "codeIndex++".
		codeIndex= codeIndex - 1;
	}

	public static void jumpForward(StringBuilder code){
		//read back with code pointer
		//count brackets until the corresponding ]
		int bracketCnt= 1;
		while(codeIndex < code.length() && bracketCnt != 0){
			codeIndex++;
			char inst= code.charAt(codeIndex);
			if(inst == ']') bracketCnt--;
			if(inst == '[') bracketCnt++;
		}
	}

	public static void input(ArrayList<Integer> mem, BufferedReader input)
			throws IOException{
		int val;
		//read until something comes in other than return chars
		for(val= input.read(); val == 10 || val == 13; val= input.read());
		mem.set(pointer, new Integer(val));
	}
}