统计某个字符串在文件中出现的次数

import java.io.BufferedReader;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;

public class Demo4 {

public int count(File file,String s){
int count = 0;
BufferedReader br = null;
try {
br = new BufferedReader(new FileReader(file));
String temp;
StringBuilder sb = new StringBuilder();
//读取文件
while((temp = br.readLine())!=null){
sb.append(temp);
}

String str = sb.toString();
//循环查找，找不到就终止循环
for (int i = 0; i < str.length(); i++) {
int index = str.indexOf(s);
if(index!=-1){
//找到以后把当前下标以前的字符串截取掉,然后用截取后的字符串循环判断
str = str.substring(index+1);
count++;
}else{
break;
}
}
} catch (FileNotFoundException e) {
System.out.println("找不到文件");
} catch (IOException e) {
e.printStackTrace();
}finally{

try {
if(br!=null)br.close();
} catch (IOException e) {
e.printStackTrace();
}
}
return count;
}

public static void main(String[] args) {
Demo4 d = new Demo4();
int count = d.count(new File("d://test.txt"), "I love china");
System.out.println(count);
}

}