印 "#" 比印 "B" 來的快的問題

這篇是兩年前在 StackOverflow 上的問題:「Why is printing “B” dramatically slower than printing “#”?」。

問問題的人這段程式跑了 8.52 秒:

Random r = new Random();
for (int i = 0; i < 1000; i++) {
    for (int j = 0; j < 1000; j++) {
        if(r.nextInt(4) == 0) {
            System.out.print("O");
        } else {
            System.out.print("#");
        }
    }

   System.out.println("");
 }

而把上面的 # 換成 B 就變成 259.152 秒。

答案是與 word-wrapping 有關:

Pure speculation is that you're using a terminal that attempts to do word-wrapping rather than character-wrapping, and treats B as a word character but # as a non-word character. So when it reaches the end of a line and searches for a place to break the line, it sees a # almost immediately and happily breaks there; whereas with the B, it has to keep searching for longer, and may have more text to wrap (which may be expensive on some terminals, e.g., outputting backspaces, then outputting spaces to overwrite the letters being wrapped).

But that's pure speculation.

這真是細節 XDDD

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