关于System.out.write(int b)

Question

这行代码我尝试读源码，发现这样一段

//FilterOutputStream.java
public void write(int b) throws IOException {
        out.write(b);
}

进一步跟踪

//OutputStream.java
private void ensureOpen() throws IOException {
        if (this.closed) {
                throw new IOException("Stream closed");
        }
}

public void write(int b) throws IOException {
        this.ensureOpen();
}

然而这段代码并没有使用参数b。有没有大佬能解答我的疑问。

Answer 1

不知道你看的是哪个版本的，我在JDK8看到的是这样的(PrintStream.java)：

     /**
     * Writes the specified byte to this stream.  If the byte is a newline and
     * automatic flushing is enabled then the <code>flush</code> method will be
     * invoked.
     *
     * <p> Note that the byte is written as given; to write a character that
     * will be translated according to the platform's default character
     * encoding, use the <code>print(char)</code> or <code>println(char)</code>
     * methods.
     *
     * @param  b  The byte to be written
     * @see #print(char)
     * @see #println(char)
     */
    public void write(int b) {
        try {
            synchronized (this) {
                ensureOpen();
                out.write(b);
                if ((b == '\n') && autoFlush)
                    out.flush();
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }