A small class for converting integers to their textual representation without creating any garbage.

NumberWriter.java

package com.tomgibara.android.util;

/**
 * <p>
 * Writes ints into char array without generating any objects. This is typically
 * useful in instances where numbers must be rendered within a game-loop or
 * animation. Instances of this class are not safe for multithreaded use.
 * </p>
 * 
 * <p>
 * Use of the class proceeds like this:
 * </p>
 * 
 * <pre>
 * <code>
 * final NumberWriter writer = new NumberWriter();
 * final char[] chars = writer.getChars();
 * final int length = chars.length;
 * ...
 * int n = 39088169;
 * int offset = writer.write(n);
 * canvas.drawText(chars, offset, length - offset, x, y, paint);
 * ...
 * </code>
 * </pre>
 * 
 * @author Tom Gibara
 * 
 */

public class NumberWriter {

	/**
	 * Big enough for a {@link Integer.MIN_VALUE}.
	 */
	private static int CHARS_LEN = 11;
	
	/**
	 * Stores the generated characters.
	 */
	
	private final char[] mChars = new char[CHARS_LEN];
	
	
	/**
	 * The character array into which numbers will be written. One character
	 * array is used for the lifetime of this object.
	 * 
	 * @return an array of characters
	 */

	public char[] getChars() {
		return mChars;
	}
	
	
	/**
	 * Writes the supplied integer to this object's character array. The
	 * characters in the integer's textual representation will begin at the
	 * returned index and continue until the end of the array.
	 * 
	 * @param n
	 *            any integer
	 * @return the index of the first character
	 */
	
	/*
	 * Note that this method could be implemented more efficiently, but it is
	 * adequate for most purposes.
	 */
	
	public int write(int n) {
		final char[] cs = mChars;
		final boolean negative;
		if (n < 0) {
			negative = true;
			n = -n;
			if (n < 0) {
				// Integer.MIN_VALUE is a special case
				cs[CHARS_LEN -  1] = '8';
				cs[CHARS_LEN -  2] = '4';
				cs[CHARS_LEN -  3] = '6';
				cs[CHARS_LEN -  4] = '3';
				cs[CHARS_LEN -  5] = '8';
				cs[CHARS_LEN -  6] = '4';
				cs[CHARS_LEN -  7] = '7';
				cs[CHARS_LEN -  8] = '4';
				cs[CHARS_LEN -  9] = '1';
				cs[CHARS_LEN - 10] = '2';
				cs[CHARS_LEN - 11] = '-';
				return CHARS_LEN - 11;
			}
		} else {
			negative = false;
		}
		int i = CHARS_LEN;
		while (n > 9) {
			final int q = n / 10;
			final int r = n - q * 10;
			cs[--i] = (char)(48 + r);
			n = q;
		}
		cs[--i] = (char)(48 + n);
		if (negative) cs[--i] = '-';
		return i;
	}
	
}