java读取文件大小

public static void main(String[] args) {
        String src = "c://test.apk";
        File file = new File(src);
        DecimalFormat df = new DecimalFormat("0.00");
        String fileSizeString = "";
         if (file.length() < 1024) {
            fileSizeString = df.format((double) file.length()) + "B";
        } else if (file.length() < 1048576) {
            fileSizeString = df.format((double) file.length() / 1024) + "K";
        } else if (file.length() < 1073741824) {
            fileSizeString = df.format((double) file.length() / 1048576) + "M";
        } else {
            fileSizeString = df.format((double) file.length() / 1073741824) + "G";
        }
         System.out.println("==========>"+fileSizeString);
    }