'M'去哪儿了？

问题描述

我在String Buffer中玩了一下，并注意到混合字符和字符串是一个坏主意。我希望我的下面的代码可以打印Main，但是只是得到了一个ain。

I played a bit around with String Buffer and noticed, that mixing chars and String is a bad idea. I expected my following code to print "Main", however just got an "ain".

显然，word是使用String Buffer构造函数的char版本初始化的，但是我测试了几个方法，比如toString或getIndex（），但在ain旁边找不到任何东西。 - 这让我想知道：构造函数做了什么？它有用吗？可以通过单词再次检索M吗？

Clearly word was initialized with the char version of the String Buffer constructor, however I tested several methods like toString or getIndex( ), but could not find anything beside "ain" - which makes me wonder: What did the constructor do? Is there a usage for it? Can the 'M' somehow be retrieved again from word ?

import java.util.Random;

public class OrNotPublicClass {
    private static Random rnd = new Random();

    public static void main(String[] args) {
        StringBuffer word = null;
        switch (rnd.nextInt(2)) {
        case 1:
            word = new StringBuffer('P');
        case 2:
            word = new StringBuffer('G');
        default:
            word = new StringBuffer('M');
        }
        word.append("ain");
        System.out.println(word);
    }
}

推荐答案

分开从中断问题，这里的主要问题是如何初始化 StringBuffer 。

Apart from the break problem, the main problem here is how you initialize your StringBuffer.

没有构造函数接受 char 作为参数， 。

There is no constructor accepting a char as an argument, but there is one accepting an int for the capacity.

这就是你使用的那个......

And that is the one you use...

你应该这样做：

word = new StringBuilder(); // not StringBuffer
// switch. Then:
word.append("ain");

（另请注意使用 StringBuilder 代替 StringBuffer ;后者仅在需要线程安全的极少数情况下有用）

(also note the use of StringBuilder instead of StringBuffer; the latter is useful only in the rare case where thread-safety is required)

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