Using static interface inner class.. how?

Can anyone tell me how I'm able to use an inner class that is a static interface?
Specifically I'm getting DocumentEvents through a DocumentListener..
Then within DocumentEvents there is an inner class which is a static interface called:
DocumentEvent.ElementChange, I'm trying to use the methods contained within the interface ElementChange.
Can anyone throw a helping hand as to how I go about this?
Thanks :)

public class A ... {
public static interface B {
}Just creates a public interface called A.B
How are you supposed to use this with your DocumentEvent? I can't say

Similar Messages

Static abstract inner classes

Sorry to sound stupid, but why would a class be static? I've encountered an example of an abstract static inner class and I'm not sure why it's static. Static methods I understand -- they are methods of the class and not the instance. So then, can someone explain to me a static class?
Thanks,
Erik

You have encountered a static nested class (not a static inner class - an inner class is a nested class that is not static).
A static nested class is a nested class that does not require an instance of its enclosing class to exist in order that it can be instantiated. - It is mainly used for code organisation, and can be treated just like a top-level class.
In practice, most nested classes (except perhaps event handlers), tend to be static.
For an example of a static nested class from the core APIs, have a look at HasMap.Entry

When we going to use static inner class

Hi
when we r going use static inner class
inner classes use for to create adaptorclasses that implement an interface.
what about Static inner class
if possible give some examples
Thanks in adv

static inner classes are used when the inner class does not require to access the encompassing class's variables/methods. By default non-static inner classes obtain a reference to the outer class instance through which they access the outer class variables and methods
ram.

Why Inner class cannot access static variables

Why is it that inner class can use only static final variables of the outerclass, and not ordinary static variables of the outer class. "Yes the JLS sepcifies that only final static variables can be used inside an inner class, esp a non blank final variable". But why this restriction.
Thanks.

so what are final static variables treated as if they
are not variables. So if the final static value is
not loaded when the class is loaded how will the
class know about the value.??The actual value wil be substituted for the name of a static final value at compile time. That's why you can use them in switch statements where you can't use any variable variable.
This is something to watch out for, by the way, because if you use a public static final value from one class in another the actual value will be compiled into the using class, so if you change the value where it's defined the class using it will have the old value until it's recompiled.

Your Opinions: Inner Classes Need static Members

Hi All,
I want to solicit opinions for a minor change to the way inner classes work. I submitted this as an RFE to Sun and they rejected it, really without giving a reason. I'd like to know your opinions. If there is strong support I will repost the RFE.
As you probably know, inner classes cannot have static members. The following generates a compiler error:import java.util.*;
public class MyClass {
   class MyInnerClass {
      // Next line causes compiler error...
      static Map m = new HashMap();
}In order to get around this you have to make the Map variable a static member of the containing class:import java.util.*;
public class MyClass {
   static Map m = new HashMap(); // so much for encapsulation...
   class MyInnerClass {
}I am suggesting that inner class be allowed to contain static members. Here's my reasoning...please comment:
There are times when members (i.e., fields and methods) rightfully belong to the class as a whole, not to any particular instance of a class. I'm sure we've all found times when it was necessary to have static members in our classes. The same issues that necessitated using static members in top-level classes make them desirable for inner classes as well.
Designing a class as an inner class is a step toward encapsulation. By forcing static members that logically belong in an inner class to be declared in the containing class is to crack the encapsulation, IMHO.
Even though a containing class has access to all of an inner class' members (including private members) and vice versa, I think the notion of inner static members still is more OO-ish.
What are your opinions? Would allowing inner classes to contain static members make Java more object oriented? I think it would.
Technically, I don't think there's any reason this cannot work since the JVM has no notion of inner classes, per se.
What do you think?

an inner class is effectively a non static instance
variable of its enclosing class. Instance member, but not a variable. it's a class, a type, not a variable.
>
I think the problem here is that making a field static
means more than just that that field and its value are
common to every instance of the class. It means that
the value is valid without an instantiation of that
class.
Since the class itself must be instantiated (it is
not static), What do you mean, excatly, by "_must_ be instantiated"? You are not ever "required" to instantiate anything unless you want to use it.
you can't have static member data inside it. I don't see how this follows from the previous part of the statement.
How would you reference the static member data of
the inner class? You would have to specify an
instance of the inner class, and since this breaks
the meaning of static, you can't have static members
in an inner class.How about outerObj.InnerClass.staticMember The syntax is well defined. The question at hand is, do we really want to allow this? The syntax to do this should only be an issue after that question has been answered in the affirmative. The people at Sun have decided not to allow it, so for now, syntax is a non-issue.
>
if you wanted a static member in an inner class you
could put it in a super class of the inner class...Or in the enclosing class, as suggested in the orginal post.

How to pass a variable value to an inner class?

Hi there,
Please have a look of the code below. It's a bit long, but my concern is I did have to declare the int "i" variable as static because it is used by an inner class (if "i" is not declare as static, the code cannot be compiled).
Is there a more "clean" way to do the way work without declaring the "i" int as static? (because the scope of this variable is not the whole program).
Thanks for your help.
Denis
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
class Tools{
 static int i;
 static void longTask(){
 for (Tools.i=0; Tools.i<=100; Tools.i++) {
 SwingUtilities.invokeLater( new Runnable(){
 public void run(){
 myApp.jpb.setValue(Tools.i);//--- static variable i
 for (int j=0; j<200; j++)
 System.out.println(Tools.i+" - "+j);
class myListener implements ActionListener{
 public void actionPerformed(ActionEvent e){
 Thread t = new Thread() {
 public void run(){
 Tools.longTask();
 t.start();
public class myApp {
 static JProgressBar jpb;
 public static void main(String[] args) {
 JFrame frame = new JFrame();
 JPanel panel = new JPanel(new FlowLayout());
 jpb = new JProgressBar();
 jpb.setValue(0);
 jpb.setStringPainted(true);
 JButton button = new JButton("go");
 button.addActionListener(new myListener());
 panel.add(jpb);
 panel.add(button);
 frame.getContentPane().add( panel, BorderLayout.CENTER);
 frame.setVisible(true);
 frame.pack();
}

Without compiling it, writing it in notepad, it would be something like this. You should also wonder if this longTask has to be static by the way. But I think this demonstrates the inner class stuff. You can also look in the tutorial on this site: http://java.sun.com/docs/books/tutorial/essential/threads/timer.html
class Tools{
 static int i;
 static void longTask(){
 for (Tools.i=0; Tools.i<=100; Tools.i++) {
 SwingUtilities.invokeLater( new Innerclass(i));
 for (int j=0; j<200; j++) {
 System.out.println(Tools.i+" - "+j);
 Class Innerclass implements Runnable(){
 int i;
 public Innerclass(int i) {
 this.i = i;
 public void run(){
 myApp.jpb.setValue(Tools.i);//--- static variable i
}

Private inner class and static private inner

Hi,
I understand the concept and usage of inner classes in general.
When should we go for a private inner class and when for a static private inner class? I tried searching but it wasn't of much help.
Basically I need to design a caching solution in which I need to timestamp the data object. After timestamping, data will be stored in a HashMap or some other collection. I'm planning to use a wrapper class (which is inner and private) which holds the data object and timestamp. I can make the program work by using either normal inner class or static inner class, however would like to know which is better in such case. Also If I can get some general guidelines as to when to use a staic inner class and when to use a normal inner class, it would help me.
Thanks in advance.

user1995721 wrote:
When should we go for a private inner class and when for a static private inner class?
I can make the program work by using either normal inner class or static inner class, however would like to know which is better
If I can get some general guidelines as to when to use a static inner class and when to use a normal inner class, it would help me.Making the inner class static is helpful in that it limits visibility.
If the inner class needs to access non-static fields or methods from the containing class instance
the inner class has to be non-static.

Why inner classes cannot have static declarations ?

Hi Friends,
When i tried to make static declarations on a inner class which is non static, i am getting compilation error saying "inner classes cannot have static declarations". I want to know reason behind this implementation.
Code which i have tried:
public class TestOuter
class TestInner{
static int i =10;
public static boolean validate(int a){
if(a==0)
System.out.println("Invalid data");
return false;
return true;
public static void main(String a[]){
boolean result = new TestOuter.TestInner.validate(0);
System.out.println("Result="+result);
Thanks,
Shiju V.

so I think if the
outer class is not static , then Inner class can't be
static as well. This is incorrect. An enclosed class can be indeed static while the outer is not, and vice versa.
The difference between static/non static in regards to enclosed classes is that the static ones are 'top-level' and cannot access the members of the enclosing class.
The effect of making an enclosed class static means there is only one instance of any variables, no matter how many instances of the outer class are created. In this situation how could the static inner class know which variables to access of its non static outer class. Of course the answer is that it could not know, and thus an static inner class cannot access instance variables of its enclosing class.
Now, regarding non-static inner classes, and trying to give a valid answer to the original post:
As with instance methods and variables, a non-static inner class is associated with an instance of its enclosing class and has direct access to that object's instance variables and methods.
TestOuter outer = new TestOuter();
TestOuter.TestInner inner = outer.new TestInner();Because an inner class is associated with an instance (inner class implicitly keeps a reference to the object of the enclosing class that created it), it cannot define any static members itself. Static members cannot access the this pointer.
So, in an ordinary (non-static) inner class, the link to the outer class object is achieved with a special this reference. A static inner class does not have that special this reference, nor would a static method/variable of an ordinary (non-static) inner class.

Assign value in a inner class

Suppose, we have the following two classes.
public class test{
final trythis t;
t = null;
doMethod(t); // because of this, t has to be assigned a null value
(new Thread(){public void run(){
t = new trythis(); // t is assigned twice
}}).start();
class trythis{
trythis(){
t seems to have to be defined as final, but final instance cannot be set in the inner class.
Does anyone know how to solve this problem?
Thanks

As the local variable has a lifetime of the executing method's
duration, you must ensure the innerclass (which has a longer lifetime)
has access to it by declaring it final.This is not quite exact. All this is due to the way inner classes are implemented. An inner class maintains the contents of the outer local variables used in two ways:
- If it is primitive, use the value verbatim (so the class has no relationship to the outer variable, it just uses the same number, so the local var needs to be final or else there could be surprises for a programmer who would think that changing the local var would also change the value used in the inner class)
- If it is a reference, copy it as a class member, and use that one wherever needed. For similar reasons as above, the two references have to be in sync, so the local var has to be final (the inner var can't change anyway)
This apply only to local variables because class members are accessible through a secret reference of the enclosing object passed in the constructor of the inner class. Static members are anyway accessible.
<teacher's mode off/>
<sorry for that, but someone might find the explanation useful :-)/>
By the way, the OP can get the value "t" out of the inner class by providing a special Thread subclass, ie
class MyThread extends Thread {
public void run() {
t = something;
trythis t;
MyThread thread = new MyThread();
thread.start();
thread.join();
thread.t; //This is accessibleI'm not sure if this would be preferable to the array approach (which is ), but it is useful to know your alternatives

PaintComponent: inner class / method?

Hi,
I am doing a lot of painting in my paintComponent method and would like to ask whether it's possible to use e.g. inner classes or methods within paintComponent? I think I am confronted with the problem that my paintComponent method gets too unstructured :-/
Thanks for your help!

I am doing a lot of painting in my paintComponent
method and would like to ask whether it's possible to
use e.g. inner classes or methods within
paintComponent? I think I am confronted with the
problem that my paintComponent method gets too
unstructured :-/paintComponent is a method... so, you can call other methods from it. I'm not sure what you mean by "use inner classes". You can define an inner class and instantiate an object of that class from within paintComponent just like you can from any other method. Your question seems a bit weird, or I'm not understanding it.
Is your paintComponent too slow or just too long? By all means, use methods to logically separate different things you are doing, but this only add organization, not speed.

The use of interface in abap object

hi,
what is the use of interface in class? can have a simple example with explanation? i have read from help but not quite understand its purpose.
thanks

Hi El,
Interfaces are pure abstract classes. The interface methods will have only definitions but no implementations.
The classes which will implement interfaces has to provide the implementation to the methods.
Interfaces will provide the common definition and the classes which implements these interfaces will provide them different implementation to the methods as per their requirements. This achieves Polymorphism of Object Orientation.
REPORT zbc404_hf_events_3 .
INTERFACE lif_employee.
METHODS:
    add_employee
       IMPORTING im_no   TYPE i
                 im_name TYPE string
                 im_wage TYPE i.
ENDINTERFACE.
CLASS lcl_company_employees DEFINITION.
PUBLIC SECTION.
    INTERFACES lif_employee.
    TYPES:
      BEGIN OF t_employee,
        no TYPE i,
        name TYPE string,
        wage TYPE i,
     END OF t_employee.
    METHODS:
      constructor,
     add_employee      "Removed
        IMPORTING im_no   TYPE i
                  im_name TYPE string
                  im_wage TYPE i,
      display_employee_list,
      display_no_of_employees.
PRIVATE SECTION.
    CLASS-DATA: i_employee_list TYPE TABLE OF t_employee,
                no_of_employees TYPE i.
ENDCLASS.
CLASS lcl_company_employees IMPLEMENTATION.
METHOD constructor.
    no_of_employees = no_of_employees + 1.
ENDMETHOD.
METHOD lif_employee~add_employee.
Adds a new employee to the list of employees
    DATA: l_employee TYPE t_employee.
    l_employee-no = im_no.
    l_employee-name = im_name.
    l_employee-wage = im_wage.
    APPEND l_employee TO i_employee_list.
ENDMETHOD.
METHOD display_employee_list.
Displays all employees and there wage
    DATA: l_employee TYPE t_employee.
    WRITE: / 'List of Employees'.
    LOOP AT i_employee_list INTO l_employee.
      WRITE: / l_employee-no, l_employee-name, l_employee-wage.
    ENDLOOP.
ENDMETHOD.
METHOD display_no_of_employees.
Displays total number of employees
    SKIP 3.
    WRITE: / 'Total number of employees:', no_of_employees.
ENDMETHOD.
ENDCLASS.
Check this link for some more examples on OO ABAP
http://www.erpgenie.com/sap/abap/OO/eg1.htm
Thanks,
Vinay

JDeveloper 10.1.2.0.0 - Inner class cannot be found

Hi! 
 
I use Apache MyFaces 1.1.1 (Nightly Build 20051130) to create a Web app and imported all necessary libraries. I want to write a custom ViewHandler at the moment and experience a strange problem. I want to use a public inner class of javax.faces.application.StateManager, named SerializedView, but this class cannot be found when I try to import it with the following statement: 
import javax.faces.application.StateManager.SerializedView; 
JDeveloper just says: 
Imported class 'javax.faces.application.StateManager.SerializedView' not found 
I already successfully use many other javax.faces classes, like StateManager... 
Any help would highly be appreciated, since this is a real blocker for me. 
 
Regards,
Matthias

Hi again! 
 
The problem is solved for the most part now. Compilation works fine, although the Java editor says the class SerializedView cannot be found. 
 
So the Java editor's behavior is still strange... 
 
Regards, 
Matthias

Event handling and inner classes

Hi everyone,
When assigning an actionlistener object to a swing component, is making the encapsulating component implement actionlistener better performance-wise than using inner classes? I ask this because my application is pretty slow to start-up, and I'm using lots of inner classes.
I don't want to go ahead and change the event-handling unless I'm sure it will do any good, because the time restriction is too tight for wasting. Does using addActionListener(this) just pass a reference to itself or is an object generated for each call?
Thanks in advance,
Richard

Passing this only passes a reference. But you won't get a big improvement over inner classes. (If you use one listener object instance and pass that instance to the event sources. Do you?)
Kurta

Private inner class

I have a private inner class , the methods and constructor of this inner class should be private or default ?Please explain me what is the right method and constructor access modifier I should use to private inner classes .

paulcw wrote:
I believe that if you make the constructor private, nothing can instantiate it.Not true for an inner class.
Re the original question: I'm not sure it really matters here, but I've not seen a canonical answer to this.

How to use a static inner class?

what's the implication of identifier "static" before an inner class.Thank you.

not sure what implication is, due to my poor vocabulary. But here's an uuh... "example" of a static inner class:
public class Example {
static class AnotherClass {
}There you have class "Example" with the static inner class "AnotherClass." If you wanted to use "AnotherClass" you would do something like:
public class Whatever {
Example.AnotherClass ac = new Example.AnotherClass();
}I don't think I'm mistaken there, but if I am someone please correct me.

Using static interface inner class.. how?

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