What is the difference between string, stringbuffer and stringbuilder?

Difference: The String class is an immutable class. When a String object is created, the character sequence contained in the object is immutable until the object is destroyed; the StringBuffer object represents a mutable string object, and Thread-safe; the StringBuilder class represents mutable string objects and is not thread-safe.

##The difference between String, StringBuffer and StringBuilder:

String

String a = "123";
a = "456";
// 打印出来的a为456
System.out.println(a)

a object

StringBuffer## The StringBuffer object represents a string with a variable character sequence. When a StringBuffer is created, the append provided by StringBuffer (), insert(), reverse(), setCharAt(), setLength() and other methods can change the character sequence of this string object. Once the final desired string is generated through the StringBuffer, you can call its toString() method to convert it into a String object.

StringBuffer b = new StringBuffer("123");
b.append("456");
// b打印结果为：123456
System.out.println(b);

 Let’s take a look at the memory space diagram of the

 So the StringBuffer object is a string with a variable character sequence. An object is not regenerated, and new strings can be concatenated into the original object.

StringBuilder The StringBuilder class also represents mutable string objects. In fact, StringBuilder and StringBuffer are basically similar, and the constructors and methods of the two classes are also basically the same. The difference is:

Methods implemented in the StringBuffer class:

Methods implemented in the StringBuilder class:

 It can be seen that the

is added to the methods in the StringBuffer class, which means a lock is added to this method to ensure thread safety.

  Java9 has improved the implementation of strings (including String, StringBuffer, and StringBuilder). Before Java 9, strings used char[] arrays to store characters, so each character in the string occupies 2 bytes; while in Java 9, strings used byte[] arrays plus an encoding-flag field to store characters, so strings Each character occupies only 1 byte. Therefore, Java9's strings are more space-saving, and the functional methods of strings are not affected.

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