java统计字符串中指定元素出现次数方法

package com.zuidaima.util.string;
import java.io.*;
public class CountString {
   
 public static int count(String filename, String target)
  throws FileNotFoundException, IOException {
  FileReader fr = new FileReader(filename);
  BufferedReader br = new BufferedReader(fr);
  StringBuilder strb = new StringBuilder();
  while (true) {
  String line = br.readLine();
  if (line == null) {
   break;
  }
  strb.append(line);
  }
  String result = strb.toString();
  int count = 0;
  int index = 0;
  while (true) {
  index = result.indexOf(target, index + 1);
  if (index > 0) {
   count++;
  } else {
   break;
  }
  }
  br.close();
  return count;
 }
   
 public static void main(String[] args) {
  try {
  System.out.println(count("D:\zuidaima.txt", "a"));
  } catch (FileNotFoundException e) {
  e.printStackTrace();
  } catch (IOException e) {
  e.printStackTrace();
  }
 }
   
}