RandomAccessFile随机访问文件

为什么需要RandomAccessFile类？

因为所有的流都是

只读的(rean-only)

或者

只写的(write-only)

,这些流被成为

顺序流(sequential stream)

,如

字符流(Reader,Writer)和字节流(InputStream,OutputStream)

使用顺序流打开的文件成为

顺序访问文件

，顺序访问的文件不能更新，所以为了经常修改文件，java提供

RandomAccessFile

类，允许从文件的任何位置进行数据的读写。使用RandoomAccessFile类打开的文件成为

随机访问文件

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());
//设置偏移量,以字节为单位
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());
}
}
}