1. 為什麼需要RandomAccessFile類？
   

因為所有的流都是只讀的(rean-only)或者只寫的(write-only),這些流被成為順序流(sequential stream),如字元流(Reader,Writer)和位元組流(InputStream,OutputStream)

使用順序流開啟的檔案成為順序訪問檔案，順序訪問的檔案不能更新，所以為了經常修改檔案，java提供RandomAccessFile類，允許從檔案的任何位置進行資料的讀寫。使用RandoomAccessFile類開啟的檔案成為隨機訪問檔案

import java.io.IOException;
import
 
 java.io.RandomAccessFile;

public class TestRandomAccessFile {
    public static void main(String[] args) throws IOException{
        try (
                RandomAccessFile inout = new RandomAccessFile("inout.dat","rw")
                ){
            inout.setLength(0);
            for (int i = 0;i<200
 
;i++){
                inout.writeInt(i);
            }

            System.out.println("current file length is "+inout.length());

            inout.seek(0);
            System.out.println("the first number is "+inout.readInt());
            //設定偏移量,以位元組為單位
            inout.seek(1*4);
            System.out.println("the second number is "
 
+inout.readInt());

            inout.seek(9*4);
            System.out.println("the tenth number is "+inout.readInt());

            inout.writeInt(555);

            inout.seek(inout.length());
            inout.writeInt(999);

            System.out.println("the new length is "+inout.length());
            inout.seek(10*4);

            System.out.println("the eleventh number is "+inout.readInt());
        }
    }
}