java源码FileInputStream
时间:2010-12-14
近做一个很简单的函数，要两个返回值，我打算有一个类封装一下返回，后来领导要求使用StringBuilder返回，不用StringBuffer，因为局部变量StringBuffer最后还是要编译为StringBuilder，因为StringBuilder没有任何同步。
问了一下大家的看法，风南说InputStream 的int read(byte[] b) 从输入流中读取一定数量的字节并将其存储在缓冲区数组 b 中，也是类似的，看来有必要研究一下IO了。
InputStream类中重要的函数，只有一个抽象的有用，
public abstract int read() throws IOException;
其他两个read的意义不大。
public int read(byte b[], int off, int len) throws IOException 和
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
下面看它的子类FileInputStream的实现，
/* File Descriptor - handle to the open file */
private FileDescriptor fd;
这个很重要，这是文件句柄，C语言使用fopen函数的都知道。
/**
* Opens the specified file for reading.
* @param name the name of the file
*/
private native void open(String name) throws FileNotFoundException;
/**
* Reads a byte of data from this input stream. This method blocks
* if no input is yet available.
*
* @return the next byte of data, or <code>-1</code> if the end of the
* file is reached.
* @exception IOException if an I/O error occurs.
*/
public native int read() throws IOException;
/**
* Reads a subarray as a sequence of bytes.
* @param b the data to be written
* @param off the start offset in the data
* @param len the number of bytes that are written
* @exception IOException If an I/O error has occurred.
*/
private native int readBytes(byte b[], int off, int len) throws IOException;
java源码FileInputStream(2)
时间:2010-12-14
子类修改了父的实现
/**
* Reads up to <code>b.length</code> bytes of data from this input
* stream into an array of bytes. This method blocks until some input
* is available.
*
* @param b the buffer into which the data is read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the file has been reached.
* @exception IOException if an I/O error occurs.
*/
public int read(byte b[]) throws IOException {
return readBytes(b, 0, b.length);
}
/**
* Reads up to <code>len</code> bytes of data from this input stream
* into an array of bytes. If <code>len</code> is not zero, the method
* blocks until some input is available; otherwise, no
* bytes are read and <code>0</code> is returned.
*
* @param b the buffer into which the data is read.
* @param off the start offset in the destination array <code>b</code>
* @param len the maximum number of bytes read.
* @return the total number of bytes read into the buffer, or
* <code>-1</code> if there is no more data because the end of
* the file has been reached.
* @exception NullPointerException If <code>b</code> is <code>null</code>.
* @exception IndexOutOfBoundsException If <code>off</code> is
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