When is `StringBuilder` is preferred instead appending `String` to `String`? [duplicate]

问题

This question already has answers here:

StringBuilder vs String concatenation in toString() in Java (18 answers)

When to use StringBuilder in Java [duplicate] (9 answers)

Closed 6 years ago.

Below are two ways how to append String:

String firstString = "text_0";
String secondString = "text_1";
String resultString = firstString + secondString;

StringBuilder sb = new StringBuilder();
sb.append(firstString).append(secondString);
String resultString = sb.toString();

My question is - when is more effective to use StringBuilder? Let's say there are 10 strings, and I need to create one of them.

回答1:

Because StringBuilder can "append" a string instead of concatenating two strings each time creating a new object. Even if you use += operator with Strings a new object is created. This advantage will only become relevant once you try to concatenate a great number of strings. If is also consiedered a bit more readable.

回答2:

Two main Advantages:

1. Mutable
2. Not Synchronized.

来源：https://stackoverflow.com/questions/18467989/when-is-stringbuilder-is-preferred-instead-appending-string-to-string