import java.io.*;

/**
 * Created by cuboo on 2016/10/10.
 */
public class io {
    public static void main(String agrs[]){
        //寫入資料
File file = new File("test.txt");
        if (!file.exists()) {
            try {
                file.createNewFile();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        new 
 
writeFile(file,6,50,"hello").start();
        new writeFile(file,1,50,"world").start();
        new writeFile(file,2,50,"this").start();
        new writeFile(file,3,50,"is - - - - - -").start();
        new writeFile(file,4,50,"block").start();

        //讀取資料
try {
            RandomAccessFile ra = new RandomAccessFile(file,"r"
 
);
            ra.seek(100);
            byte bys[] = new byte[10];
            ra.read(bys);
//            System.out.println(ra.readLine());
System.out.println(new String(bys));

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

class 
 
writeFile extends Thread {
    File in;
    int block;  //塊下標
int length; //每個塊的長度
String text;
    writeFile(File in,int block,int length,String text){
        this.in = in;
        this.block = block;
        this.length = length;
        this.text = text;
    }

    @Override
public void run() {
        try {
            RandomAccessFile ra = new RandomAccessFile(in,"rw");
            /*
            *  file in 的內容
            *  block 1          block  2            block  3
            * |...................|.....................|
            * |.......length......|........length.......|
             */
ra.seek((block-1)*length);//指向block
ra.writeBytes(text+block);
            ra.writeBytes("\n");
            ra.close();

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}