data compression

package ir.javacup.cmp;

public class Compression {

	public String compress(String data) {
		if(data==null) return null;
		if(data.isEmpty()) return "";
		String t="";
		int rep=1;
		char b=data.charAt(0);
		for(int j=1;j<data.length();j++)
		{
			if(samechar(data.charAt(j),b))
				rep++;
			else
			{
				if(rep>2) {
					t=t+rep+makelow(b);
				}
				else 
				{
					t+=(data.substring(j-rep,j));
				}
				
				rep=1;
				b=data.charAt(j);
			}
		}
		
		if(rep>2) {
				t=t+rep+makelow(b);
		}
		else 
		{
			t+=(data.substring(data.length()-rep,data.length()));
		}
		return t;
	}

boolean samechar(char c,char t)
{
	return makelow(c)==makelow(t);
}
char makelow(char c)
{
	if(c>='a' && c<='z') return c;
	else if(c>='A' && c<='Z') return (char)(c-'A'+'a');
	return c;
}

	public static void main(String[] args) {
		System.out.println(new Compression().compress("")); //prints: abb63753c
		System.out.println(new Compression().compress("aabddc")); //prints: aabddc
		System.out.println(new Compression().compress("AaaABbbcdefGG")); //prints: 4a3bcdefGG
	}
}