On the difference between null and "" in Java

In Java, we usually have to initialize a string when we first recognize it as "", or do not give him a value so that he defaults to null.

First we say that the two symbols are different, the difference is that NULL is not the meaning, and "" This refers to the existence of a blank. If we create an object that assigns a value to null then it means that only one variable name is created in the heap, and there is no

The stack creates space for it, and if an object is assigned a value of "" then it is not only creating the variable name in the pair, but also opening up a blank space in the stack.

As for what I did after creating the variable null when to create "", this is like in the next code:

public Boolean verification () {
String a = T1.gettext ();
String B = T2.gettext ();
String C = T3.gettext ();
String d = t4.gettext ();
String error = "";
if (A.matches ("[a-za-z\\u4e00-\\u9fa5]{2,9}")!=true) {
Error + = "Name Please enter 2-9 Chinese or English letters \ n";
System.out.println (a);
}
if (C.matches ("[\\u4e00-\\u9fa5]{1}")!=true) {
error+= "Gender please use a Chinese description \ n";
}
if (B.matches ("[0-9]{2}")!=true) {
error+= "name is two digits \ n";
}
if (D.matches ("(13|15|18) [0-9]{9}")!=true) {
error+= "Phone number is 13 or 15 or 18 starts with 11 digits \ n";
}
if (Error.length () ==0) {
Joptionpane.showmessagedialog (NULL, "add success");
return true;

}
else{
Joptionpane.showmessagedialog (null, error);
return false;
}

}

If we assign the initial value of the error to null, then we will have a null pointer error in the next call to Error.length (), where we can only assign it as "".

And in some just receive output, do not need to call the string method of the place can be directly without assignment, directly let it default to null.

On the difference between null and "" in Java