String StringBuffer stringBuilder 区别

String, StringBuffer, and StringBuilder are all classes in Java that represent sequences of characters.

Here are some key differences between them:

1. String objects are immutable, which means that once they are created, their values cannot be changed. In contrast, StringBuffer and StringBuilder objects are mutable - you can add, delete, or modify their contents.
2. When you perform a modification on a StringBuffer object, it happens in place (i.e., the object itself is modified). On the other hand, when you perform a modification on a StringBuilder object, a new object is created with the modified content.
3. StringBuffer is synchronized, which means that it is thread-safe - multiple threads can access it without causing any problems. StringBuilder is not synchronized, and therefore is not thread-safe. This makes StringBuilder faster than StringBuffer in situations where thread-safety is not necessary.
4. StringBuffer was introduced in Java 1.0, while StringBuilder was introduced in Java 5.0.

In general, if you need to modify a string frequently or in a multithreaded environment, it is better to use StringBuffer. If you need to modify a string frequently in a single-threaded environment, or if you just need an efficient way to concatenate strings, StringBuilder is a good choice. However, for most simple string manipulation tasks, String is sufficient.