根据自己的实际需要修改存放的地址和循环的次数

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

public class Test {
	public static void main(String[] args) throws IOException {
        //根据自己实际地址来写路径
		FileWriter fileWriter = new FileWriter(new File("E:/80M.txt")); 
        BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
       //4000000大概能生成60M的文件 
        for (int i = 0; i <4000000; i++) { 
            bufferedWriter.write("abcdefghijklmnopqist"); 
        } 
        bufferedWriter.flush(); 
        bufferedWriter.close(); 
        FileReader fileReader = new FileReader(new File("E:/80M.txt")); 
        BufferedReader bufferedReader = new BufferedReader(fileReader); 
        bufferedReader.skip(1000000l); 
        char[] bs = new char[1]; 
        bufferedReader.read(bs); 
        System.out.println(bs[0]); 
	}

}