Java 數組輸出

Java 數組輸出

Java 數組輸出一般都是用循環輸出，例如（code1）：

		int[] arr = new int[10];
		for (int i = 0; i < arr.length; i++) {
			System.out.print(arr[i]);
		}

但是，對於 char[] 類型的數組，可以使用一條輸出語句輸出，例如（code2）：

		char[] chs = { 'a', 'b', 'c', 'd' };
		System.out.println(chs);

注意 code1 和 code2 中兩條打印語句的區別：

		System.out.print(arr[i]);//code1
		System.out.println(chs);//code2

打印 int 數組 arr 的時候沒有換行，因爲是 System.out.print(); 打印 char 數組 chs 的時候，中間也沒有換行，就好像是把 chs 數組內容當成了一個字符串打印一樣。

char 數組之所以可以這樣直接輸出，是因爲源碼中的實現：

void java.io.PrintStream.println(char[] x)

    /**
     * Prints an array of characters and then terminate the line.  This method
     * behaves as though it invokes <code>{@link #print(char[])}</code> and
     * then <code>{@link #println()}</code>.
     *
     * @param x  an array of chars to print.
     */
    public void println(char x[]) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }

void java.io.PrintStream.print(char[] s)

    /**
     * Prints an array of characters.  The characters are converted into bytes
     * according to the platform's default character encoding, and these bytes
     * are written in exactly the manner of the
     * <code>{@link #write(int)}</code> method.
     *
     * @param      s   The array of chars to be printed
     *
     * @throws  NullPointerException  If <code>s</code> is <code>null</code>
     */
    public void print(char s[]) {
        write(s);
    }

void java.io.PrintStream.write(char[] buf)

    /*
     * The following private methods on the text- and character-output streams
     * always flush the stream buffers, so that writes to the underlying byte
     * stream occur as promptly as with the original PrintStream.
     */

    private void write(char buf[]) {
        try {
            synchronized (this) {
                ensureOpen();
                textOut.write(buf);
                textOut.flushBuffer();
                charOut.flushBuffer();
                if (autoFlush) {
                    for (int i = 0; i < buf.length; i++)
                        if (buf[i] == '\n')
                            out.flush();
                }
            }
        }
        catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        }
        catch (IOException x) {
            trouble = true;
        }
    }

textOut 是 BufferedWriter 對象,代表着向控制檯輸出信息的輸出流對象。charOut 是 OutputStreamWriter 對象,是用來將字節轉換成字符的轉換流對象。textOut 包裝了 charOut
textOut.write(buf);調用到以下方法：

    /**
     * Writes an array of characters.
     *
     * @param  cbuf
     *         Array of characters to be written
     *
     * @throws  IOException
     *          If an I/O error occurs
     */
    public void write(char cbuf[]) throws IOException {
        write(cbuf, 0, cbuf.length);
    }

該方法就是將 char 數組的每個字符挨個輸出到控制檯中。

總結一句話，其實 System.out.println(c); 就是將 c 數組的每個字符挨個輸出到控制檯中。