Forward Declaration and "this" keyword

Consider this code:
class A {
   private int i = 2 * this.j; // This will be calculated as 2 * 0 = 0
//   private int i = 2 * j; //This code will not compile
   private int j = 20;
}Why the "this" keyword is required for the j to be accessible? Though it is a forward declaration, what is the significance of "this" which gives visibility to the variable j. Please give some light to this.

Though it is a forward declaration, what is the significance of "this" which gives
visibility to the variable jI don't think "this" alters the visibility of j: that is the instance variable j is in scope. However "Use of instance variables whose declarations appear textually after the use is sometimes restricted, even though these instance variables are in scope."
See "8.3.2.3 Restrictions on the use of Fields during Initialization" http://java.sun.com/docs/books/jls/third_edition/html/classes.html#287410
Using "this" you have a reference to the object being constructed with the j instance variable sill having its default value of zero.
Such instance initialisers would appear to be inherently less intelligible than using a constructor.

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Package forward declaration

Can anyone kindly explain me in detail about Package forward declaration and where this is used and what's the purpose of using it.A example would be good
Thanks in advance

A subprogram declaration called a
forward declaration. It consists of the subprogram
specification in the package body .
CREATE OR REPLACE PACKAGE BODY declare_forward
IS
PROCEDURE pro(. . .);      -- forward declaration
PROCEDURE pro2(. . .)
IS                         -- subprograms defined
BEGIN           -- in alphabetical order
pro(. . .);
END;
END declare_forward;

This and super keywords, array.length attribute

'this' and 'super' keywords and array.length attribute are declared in which java class?
and also during running of a java program how they are initialized and how they work?

'this' and 'super' keywords and array.length attribute are declared in which java class?They are not declared in any Java class, any more than the keywords 'class', 'interface', 'for', 'while', etc., are. They are defined in the grammar of the Java language, in the Java Language Specification.
and also during running of a java program how they are initialized and how they work?That's much too large a question for a forum. Try reading the Java Tutorial.

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Thanks.

Maybe I'm missing something but how can Verizon have control over your personal GMail account? Sounds like you do have your email set up to forward to sms.
I have certain emails that are forwarded to me as SMS but that is an option that is enabled on the email side of things and is independent from Verizon.

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I'm glad it solved your problem

This and super keyword

what is the difference between this and super keyword?

this serves as a reference to the current object whilst super refers to the superclass of the current object.

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Using "this" keyword

Please help me. I didn't find an explanation in manuals or tutorials. Thank you
//THIS PROGRAM IS WORKING BUT I CANNOT UNDERSTAND IT
class one{
     public one(){
     System.out.println("This is from constructor");
     //PLEASE MAKE ME UNDERSTAND THIS METHOD IN THE WAY IT IS DECLARED "one two()"!!!!!!!!
     //I'M ALSO CONFUSED ABOUT THE USE OF "THIS" KEYWORD
     one two(){
          System.out.println("This is from method two()");
          return this;
class From_main{
     public static void main(String[] args){
          one a=new one();
          one b=new one();
          a.two();
          b.two();
     }

IMHO the trouble with cute trivial Examples like this is that; the names are meaningless and/or tend to confuse
and they don't represent anything useful that you might do in real life.
It might help if we renamed the class and methods and added some comments
class Trivial {
public Trivial(){
    System.out.println("This is from constructor");
/** Returns a reference to an instance of this class */
Trivial getInstance(){
    System.out.println("This is from method getInstance()");
    return this;
class From_main {
public static void main(String[] args){
    Trivial a = new Trivial();
    Trivial b = new Trivial();
    Trivial aa = a.getInstance();
    // a and aa point to the same 'Trivial' instance
    if ( a == aa)
      System.out.println("a == aa");
    Trivial bb = b.getInstance();
    // b and bb point to the same 'Trivial' instance
    if ( b == bb)
      System.out.println("b == bb");
}The method getInstance() is redundant as you have to have a reference to the object
before you can invoke the method to get a reference to the object.
There are better ways to illustrate how to use the 'this' keyword.

Forward Declaration in Class Builder

Hi All,
In the Class Builder (SE24)when i create a new Class, There is an option of Forward declaration in the Property Tab. In this, we can add Type Group Interface and Class. What is the Purpose of this forward declaration?
The F1 help does not provide any help.
Regards,
Kapil.

in addition to above replies, it can be used for classes and interfaces in that case Forward declaration is equivalent to
CLASS <class_name> DEFINITION LOAD.
interface <interface_name> load
statements which are normally used in Program ( case for local classes )
use of Load from SAP docu
... LOAD
Effect
The variant with the LOAD addition loads a global class class from the Class Library. This statement was needed before Release 6.20 if you wanted to access one of the static components of class from within a program, or to declare an event handler for class before class had been loaded automatically. From Release 6.20 onwards, the LOAD addition is only needed if the compilation of an ABAP program fails because it includes recursive accesses of a globa l class. In such cases, you may be able to make the program compilable by explicitly loading the class before recursion.
Thanks,
kranthi.

Use of forward declaration

Hi Experts,
Please let me know the use of forward declaration for a class. How to use that?
Thanks and Regards,
Debarshi

Hi,
Absolutely true matt...
you use forward declaration when you want to indicate that this component will be defined later but i am referring to this as of now.
so that it does not give any syntax/ run time error.
Rgds/Abhi

No logical forward declared in action {0} in Web Channel

Hello
We are getting this error (No logical forward declared in action ) in CRM Web Channel when we are trying to retrieve a service order.
Any Ideas????

Hello,
I would guess that this maybe due to come config in your struts-config.xml
I would check the f tansaction type that is been used and the transaction category
The only transaction category working with ICSS are:
- BUS2000116
- BUS2000120
- BUS2000112
Regards
Mark

Querstion regarding the "this" keyword

hi everyone,
i've doubt regarding the usage of this keyword in the inner classes & static methods. like the following:
class A {
    int val1 = 0;
    int val2 = 0;
    A() {
        B b = new B();
        C c = new C();
        for(int i=1; i < 11; i++) {
            b.add(i);
            c.add(i);
            System.out.println("Val 1 : " + val1);
            System.out.println("Val 2 : " + val2);
    public static void main(String args[]) {
        new A();
    class B {
        public void add(int val) {
            // the this keyword is used as static variable
            A.this.val1 += val;
    static class C {
        public void add(int val) {
            // the "this" keyword cannot be used
            //A.this.val2 += val;
}the code doesn't matter what its meant for, i wrote code to explain u my doubt with example.
so any explanation from ur side, i'm not clear with the this keyword usage.
thanx

I am in agreement with trinta, although I think your doubt arises from a lack of understanding of inner classes, not from the use of 'this'. You seem very adept in the use of 'this'.
Realise that there are 4 categories of nested classes:
1> Top-level or static nested classes
These are declared by the static keyword (as in class C in your example). They can be instantiated with or without an instance of the containing class. i.e. using the class names from your example.
C c = new A.C();
or
C c = new instanceOfA.C();
Since a static nested class does not require an instance of a class, there is no use of the 'this' keyword. There may not be any instance created, if if there was, which one since you don't have to specify which when creating it (see first example code above).
2> Member Inner Classes
As in class B in your example. The name should indicate that we think about these classes as members, or part of, the containing instance. Use these classes when it makes no sense for the inner class to exist outside the containing class. Usually these inner classes are designed to be helper classes and often hidden from view. When they aren't, the only way to create new instances of them is through an actual instance of the containing class. i.e. using the class names from your example,
B b = new instanceOfA.B();
Note that this code
B b = new A.B();
will yield an error. There must be an associated containing class.
For this reason, the use of 'this' is only appropriate for member classes.
3> Local Inner Classes
4> Anonymous Inner Classes
Not really relevant to this question.

Receiving the warning of class forward declaration

I am trying to build the Clustering Plug in project on my Leopard. I have following 2 queries -
In that project an interface class is defined as
@interface ClusteringController : NSWindowController { ....... ..... .... } @end.
And this class is used in implementation class using forward declaration as follows
@class ClusteringController;
then in one fuction it is used as follows
(long) filterImage:(NSString*) menuName {
ClusteringController *cluster = [[ClusteringController alloc] init]; [cluster showWindow:self]; return 0; }
When i try to build this project it showing a warning as follows
warning: receiver 'ClusteringController' is a forward class and corresponding @interface may not exist
Also there is 1 more warning is coming
warning: no '-updateProxyWhenReconnect' method found
This warning is coming for the following line of code
if(delegate) [delegate updateProxyWhenReconnect];
Can anybody help me to overcome these warnings?

shaktirsg wrote:
And this class is used in implementation class using forward declaration as follows
@class ClusteringController;
An implementation requires an #import of the entire interface file for any class used in the code. As a rule:
Use @class when a class is used in an @interface
Use #import when a class is used in an @implementation
if(delegate) \[delegate updateProxyWhenReconnect\];
warning: no '- updateProxyWhenReconnect' method found
It looks like the compiler doesn't know the class of 'delegate'. Can we see the code that sets the 'delegate' variable? Also please let us know where updateProxyWhenReconnect is declared. Is it declared in the interface for the class to which 'delegate' belongs? If so, it might be good for us to also see that @interface file.
\- Ray

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Thanks in advance. I look forward to learning about this.

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Regards
TD

Forward Declaration and "this" keyword

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