In Java, variables cannot contain objects, but only references to objects.
The objects are constructed and allocated in memory independently from the declarations of variables. Specifically:
A variable whose type is a class contains a reference to an object of the class (i.e., the address of the memory location where the object is allocated).
String s; s = "xxx";
The first statement declares a variable s of type String. Such a variable is not initialized yet. The second statement assign to such a variable the reference to the object denoted by "xxx".
Notice that two variables may contain a reference to the same object.
String s, t; s = "xxx"; t = s;
After these two statement, both t and s contain a reference to the object denoted by "xxx".
Variables of type object reference may have also a special value, namely null. Such a value means that the variable does not denote any object. Do not confuse variables whose value is null with variables that are not initialized. A variable that is not initialized does not have any value, not even null.