package test;

import java.io.*;

public class test4 {
	public static void main(String[] args) throws IOException
	{
		OutputStream out = new FileOutputStream("./test.txt");
		String a = "123456789";
		byte[] buff = a.getBytes();
		
		int len=3;
		out.write(buff, 0, 3);
		out.flush();
		out.write(buff, 0, 4);
		
		
		out.close();
	}
}


package test;

import java.io.*;

public class test4 {
	public static void main(String[] args) throws IOException
	{
		OutputStream out = new FileOutputStream("./test.txt");
		String a = "123456789";
		byte[] buff = a.getBytes();
		
		int len=3;
		out.write(buff, 0, 3);
		out.write(buff, 3, 4);
		
		
		out.close();
	}
}

 

 

write(byte[] b, int off, int len)

其中off和len都不允许为负值

 

off是相对与你的字节数组，即buff的偏移量

len是从off那个偏移位置开始写几个字节

 

文件的写入默认的是一点点往后加的，即C语言的fwrite(buffer,size,count,fp);

C:  要想实现改变对文件读写的偏移指针需要用fseek();

Java: 要想实现改变对文件读写的偏移指针需要用RandomAccessFile类中的seek();

 

另外OutputStream out = new FileOutputStream("./test.txt",true);为追加写入，即在原文件后追加写入。