CodeEval - Lettercase Percentage Ratio - Easy

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.StringTokenizer;

public class Main {

    public static void main(String[] args) throws FileNotFoundException, IOException {

    File file = new File(args[0]);
    BufferedReader in = new BufferedReader(new FileReader(file));
        StringBuffer sb=new StringBuffer();
        String line;
        while ((line = in.readLine()) != null) {
            int counter=0;
            int n=0;
            for(int i=0;i<line.length();i++){
                char c=line.charAt(i);
                if(c>='a'&&c<='z'){
                    counter++;
                    n++;
                }else if(c>='A'&&c<='Z'){
                    n++;
                }
            }
            sb.append(String.format("lowercase: %.2f uppercase: %.2f", (counter*100.0)/n,((n-counter)*100.0)/n)).append('\n');
        }
        System.out.print(sb);
    }
   
}