Java String vs StringBuilder [英] Java String vs StringBuilder

问题描述

据我所知Java字符串中的 +运算符重载，并且当我们使用 + 运算符时，它会自动选择StringBuffer或StringBuilder来连接具有更好性能的字符串.唯一的例外是在循环中使用 + 运算符时.在这种情况下，Java不使用StringBuffer和StringBuilder的好处.真的吗?我将连接40个字符串(大约4500个字符)，并且我会经常重复它，所以我想确定一下.

As far as i know + operator in Java String is overloaded and while we are using + operator it automatically chooses StringBuffer or StringBuilder to concatenate strings with better performance. Only exception of this is while we are using + operator inside a loop. In this case Java doesn't use benefits of StringBuffer and StringBuilder. Is that true? I will concatenate 40 Strings (around 4500 chars) and I will repeat it so often so I wanted be sure about it.

推荐答案

不，Java会总是(ss总是)(几乎总是在下面的注释中)将串联转换为 StringBuilder .但是，循环的问题在于，它将在每个演练中创建 StringBuilder 的新实例.

No, Java will always (almost always, see comment bellow) convert concatenation into the StringBuilder. However the problem with loop is that it will create new instance of StringBuilder per each walkthrough.

因此，如果您在从 0 到 1000 的循环中执行 String someString = i +"something"; 您新的 StringBuilder 实例1000次.那么这可能是性能问题.因此，只需在循环之前声明 StringBuilder ，然后在循环内部使用它即可.

So if you do String someString = i + "something"; inside the loop which goes from 0 to 1000 it will create for you new instance of StringBuilder 1000 times. Which could be a performance problem then. So just declare StringBuilder before the loop and then use it inside it.

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