String A in Java; The difference between string a = null and string a = ""

String A; Declares a string type A, which does not have a memory address in the request, nor any point in memory to the reference address;

String a = null; Declare a string of type A, while in memory requested an address, but the address does not point to any reference address;

String a = ""; Declare a string of type A, both in the memory of the application of the address, which also points to a reference to the string reference address;

It is generally best to use string a = "" for strings, and to prevent exceptions that are not found by the subsequent program because of a confusing reference address! String a = null; String A; Use less strength! No need to use it!

String A in Java; The difference between string a = null and string a = ""