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(); 
  } 
 } 
  
}