读源码之旅 java.io包

对于下图，研究了一下常用的InputStream,ByteArrayInputStream,BufferedInputStream,FileIputStream,ObjectInputStream，DataInputStream 以及相对应的OutStream类。



看完还是有一些收获的：
1、对其整体结构更清晰了一些，基本上在什么场合想用哪一个流心里都比较有数了。

2、明白了为什么一些类在write后，还要flush一下。举一个例子，看一下BufferedOutputStream里面的几个方法就明白

public synchronized void write(int b) throws IOException {
	if (count >= buf.length) {
	    flushBuffer();
	}
	buf[count++] = (byte)b; //这里的write作用是把数组放入buf数组，作当缓冲
    }
    public synchronized void flush() throws IOException {
        flushBuffer(); //写入数据
	out.flush();   //调用包装的类的flush方法
    }
    private void flushBuffer() throws IOException {
        if (count > 0) {
	    out.write(buf, 0, count);
	    count = 0;
        }
    }

3、有一些Stream关闭不关闭都是一样的，例如像 ByteArrayInputStream

4、ByteArrayInputStream类有如下方法:
 

public synchronized int read() {
	return (pos < count) ? (buf[pos++] & 0xff) : -1;
    }

   注意这里的 0xff，搜索一些资料

引用

0xFF is hexadecimal, you can Wikipedia that part.
FF is a representation of
00000000 00000000 00000000 11111111
(a 32-bit integer)
& means bit-wise "and", and so when you use it on two ints, each pair of bits from those two ints is and-ed and the result is placed in the resultant int:
Example (showing 16 bits only)

0101 1100 1010 1100
&0000 0000 1111 1111
-----------------
=0000 0000 1010 1100

引用

Bytes are signed in Java. In binary 0x00 is 0, 0x01 is 1 and so on but all 1s (ie 0xFF) is -1, oxFE is -2 and so on. See Two's complement, which is the binary encoding mechanism used.
http://en.wikipedia.org/wiki/Two's_complement

5、比较复杂的类：ObjectOutputStream,要花多一些时间去看

6、研究RandomAccessFile类，可以复习一下按位运算符。
运算符 符号
按位与 &
按位左移 <<
按位取反 ~
按位或 |
按位右移 >>
按位异或 ^
无符号右移 >>>