run length encode a string

RLE.java

import java.util.*;

public class Test
{
	static String rle(String input) {
		if (input == null || input.equals("")) return "";
		StringBuilder sb = new StringBuilder();
		int i = 0;
		while (i < input.length()) {
			int j = 1;
			while (i + j < input.length() && input.charAt(i) == input.charAt(i+j)) ++j;
			sb.append(input.charAt(i)).append(j);
			i += j;
		}
		return sb.toString();
	}

	public static void main(String[] args) {
		System.out.println(rle("aabbaadddc")); // a2b2a2d3c1
	}
}