Обратимся к источнику

Prentice Hall - Core Java 2 Volume I - Fundamentals 7th.chm
There is an important difference between objects and object variables. For example, the statement

Date deadline; // deadline doesn't refer to any object

defines an object variable, deadline, that can refer to objects of type Date. It is important to realize that the variable deadline is not an object and, in fact, does not yet even refer to an object. You cannot use any Date methods on this variable at this time. The statement

s = deadline.toString(); // not yet

would cause a compile-time error.

You must first initialize the deadline variable. You have two choices. Of course, you can initialize the variable with a newly constructed object:

deadline = new Date();

Or you can set the variable to refer to an existing object:

deadline = birthday;

Now both variables refer to the same object.


It is important to realize that an object variable doesn't actually contain an object. It only refers to an object.

In Java, the value of any object variable is a reference to an object that is stored elsewhere. The return value of the new operator is also a reference. A statement such as

Date deadline = new Date();

has two parts. The expression new Date() makes an object of type Date, and its value is a reference to that newly created object. That reference is then stored in the deadline variable.

You can explicitly set an object variable to null to indicate that it currently refers to no object.

deadline = null;
. . .
if (deadline != null)
System.out.println(deadline);

If you apply a method to a variable that holds null, then a runtime error occurs.

birthday = null;
String s = birthday.toString(); // runtime error!

Variables are not automatically initialized to null. You must initialize them, either by calling new or by setting them to null.



//

Many people mistakenly believe that Java object variables behave like C++ references. But in C++ there are no null references, and references cannot be assigned. You should think of Java object variables as analogous to object pointers in C++. For example,

Date birthday; // Java



is really the same as

Date* birthday; // C++



Once you make this association, everything falls into place. Of course, a Date* pointer isn't initialized until you initialize it with a call to new. The syntax is almost the same in C++ and Java.

Date* birthday = new Date(); // C++



If you copy one variable to another, then both variables refer to the same date—they are pointers to the same object. The equivalent of the Java null reference is the C++ NULL pointer.

All Java objects live on the heap. When an object contains another object variable, that variable still contains just a pointer to yet another heap object.

In C++, pointers make you nervous because they are so error prone. It is easy to create bad pointers or to mess up memory management. In Java, these problems simply go away. If you use an uninitialized pointer, the runtime system will reliably generate a runtime error instead of producing random results. You don't worry about memory management, because the garbage collector takes care of it.

C++ makes quite an effort, with its support for copy constructors and assignment operators, to allow the implementation of objects that copy themselves automatically. For example, a copy of a linked list is a new linked list with the same contents but with an independent set of links. This makes it possible to design classes with the same copy behavior as the built-in types. In Java, you must use the clone method to get a complete copy of an object.

Primax
а как тогда они называются ? Например :

Object ob;

что такое ob ?
Это неинициализированная объектная переменная.
После
ob станет указателем на объект.

Неиспорченным C++'ом можно называть их ссылками (потому что они всё-равно не знают, что такое ссылка). Но лучше не надо.

Primax
PS не судите строго...я только учу Яву )
Кстати, почему бы вам не почитать указанный мной источник? И только потом задавать свои вопросы?

joybell0
А сам-то прочитал? ;)

Ну вашу мать. Специально привел, чтобы вы дочитали до конца.
автор

Many people mistakenly believe that Java object variables behave like C++ references. But in C++ there are no null references, and references cannot be assigned. You should think of Java object variables as analogous to object pointers in C++ .

Это и есть указатели на объект.

Похоже, вы не испорчены C++, юные падаваны :)

Если вы хотите двинуться в дебри этимологии, велкам.
Давайте обсудим, что можно считать ссылкой, а что — указателем.

Timm
Лучше к http://java.sun.com/docs/books/jls/third_edition/html/typesValues.html] перво источнику . Там где то есть упоминание "object variable"?
А меня тут не обвиняли в жонглировании "object variable".
Кстати, тынц
The reference values (often just references) are pointers to these objects, and a special null reference, which refers to no object.

Timm
"Object reference" скрывает разделение между "reference variable" и "reference value".
PS. отличная статья в тему. поржать :)
В Java есть лишь reference variable. Потому что reference value в ней нет по определению. Если не считать reference value как object pointer. Или я неправ?

Timm
PS. отличная статья в тему. поржать :)
Фу. Там про дур.