Understanding of String and StringBuffer

Both String and StringBuffer can store and operate strings, that is, String data containing multiple characters.
 
The String class is a String constant and cannot be changed. StringBuffer is a string variable, and its objects can be expanded and modified.
 
StringBuffer class Constructor
 
Public StringBuffer ()
 
Create an empty StringBuffer class object.
 
Public StringBuffer (int length)
 
Create a StringBuffer class object with the length parameter.
 
Note: If the length is smaller than 0, the NegativeArraySizeException is triggered.
 
Public StringBuffer (String str)
 
Use an existing String constant to create the StringBuffer class object.