1,随机生成一个500m的txt,填充内容为小写的26个字母。生成后，查找abc字符，打印出其数量和位置(越快越好)

package com.baoge.test;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.Date;
import java.util.Random;

public class Test1  {
    
    public static void main(String[] args) throws IOException {
        File file = new File("D://test.txt");
        writeFile(file);
        readFile(file);
    }
    
    public static void writeFile(File file) throws IOException{
        
        //1m=1024kb , 1kb = 1024byte,gbk编码中一个英文字符占一个字节。
        int fileSize = 500*1024*1024;
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file)));
        Random random = new Random();
        System.out.println("start time="+new Date());
        int i = 0;
        while( i < fileSize ){
            int num = random.nextInt(26);//生成随机数，大于等于0，小于26
            char c = (char) (num+97);//a:97,b:98.....,z:122
            bw.write(""+c);
            i ++;
        }
        bw.flush();
        bw.close();
        System.out.println("end time="+new Date());
    }
    
    public static void readFile(File file) throws IOException {
        
        BufferedReader br = new BufferedReader(new InputStreamReader(new FileInputStream(file)));

        int index = 0;
        int count = 0;
        
        char[] chars = new char[3];
        
        while(br.read(chars, 0, 3)>-1){
            String str = new String(chars);
            
            if(str.equals("abc")){
                count ++;
                System.out.println("数量："+count+"---位置："+index);
            }
            index += 3;
        }
        
        br.close();
    }
}