is string in Java fixed-length? Why "+" connection is available

The so-called length fixation is not what you understand.
instead, the char["stored in the string class] is final and cannot be modified, and your operation on string actually produces a new string, which is fixed for a string.

string s = "asdf"; When you define this variable, the Jvm-java virtual opportunity assigns a string constant ASDF to an address in the memory stack based on the Java object pooling mechanism, and you
You can refer to the J2SE API, and you will find that the variable of type string is
You cannot continue appending characters like StringBuffer (that is, after appending a character, it is not the original object).
So using the ' + ' hyphen s = s+ "X", the JVM then generates a new string constant on the stack.

is string in Java fixed-length? Why "+" connection is available