Outer Class Accessing Inner Classes Variables

Hi Everyone,
Should an outer class directly access the private member variables of its inner class? Or should it get their values by calling an appropriate 'getXXX()' method?
Just wondering.
Thx.

If the outer class trys to access the variable that is declared in the inner class with in a class and outside the method, then it can access in the following example
class outer
     private int x=10;
     class inner
          int y=20;
     public void getOutput()
          inner in=new inner();
          System.out.println("The value of y is" +in.y);
     public static void main(String args[])
          outer out=new outer();
          out.getOutput();
};

Similar Messages

How to access var in outter class inside inner class

I've problem with this, how to access var number1 and number2 at outter class inside inner class? what statement do i have to use to access it ? i tried with " int number1 = Kalkulator1.this.number1; " but there no value at class option var y when the program was running...
import java.io.*;
public class Kalkulator1{
int number1,number2,x;
/* The short way to create instance object for input console*/
private static BufferedReader stdin =
new BufferedReader( new InputStreamReader( System.in ) );
public static void main(String[] args)throws IOException {
System.out.println("---------------------------------------");
System.out.println("Kalkulator Sayur by Cumi ");
System.out.println("---------------------------------------");
System.out.println("Tentukan jenis operasi bilangan [0-4] ");
System.out.println(" 1. Penjumlahan ");
System.out.println(" 2. Pengurangan ");
System.out.println(" 3. Perkalian ");
System.out.println(" 4. Pembagian ");
System.out.println("---------------------------------------");
System.out.print(" Masukan jenis operasi : ");
String ops = stdin.readLine();
     int numberops = Integer.parseInt( ops );
System.out.print("Masukan Bilangan ke-1 : ");
String input1 = stdin.readLine();
int number1 = Integer.parseInt( input1 );
System.out.print("Masukan Bilangan ke-2 : ");
String input2 = stdin.readLine();
int number2 = Integer.parseInt( input2 );
     Kalkulator1 op = new Kalkulator1();
Kalkulator1.option b = op.new option();
     b.pilihan(numberops);
System.out.println("Bilangan yang dimasukkan adalah = " + number1 +" dan "+ number2 );
class option{
int x,y;
     int number1 = Kalkulator1.this.number1;
     int number2 = Kalkulator1.this.number2;
void pilihan(int x) {
if (x == 1)
{System.out.println("Operasi yang digunakan adalah Penjumlahan");
        int y = (number1+number2);
        System.out.println("Hasil dari operasi adalah = " + y);}
else
{if (x == 2) {System.out.println("Operasi yang digunakan adalah Pengurangan");
         int y = (number1-number2);
         System.out.println("Hasil dari operasi adalah = " + y);}
else
{if (x == 3) {System.out.println("Operasi yang digunakan adalah Perkalian");
         int y = (number1*number2);
         System.out.println("Hasil dari operasi adalah = " + y);}
else
{if (x == 4) {System.out.println("Operasi yang digunakan adalah Pembagian ");
         int y = (number1/number2);
         System.out.println("Hasil dari operasi adalah =" + y);}
else {System.out.println( "Operasi yang digunakan adalah Pembagian ");
}

Delete the variables number1 and number2 from your inner class. Your inner class can access the variables in the outer class directly. Unless you need the inner and outer class variables to hold different values then you can give them different names.
In future place code tags around your code to make it retain formatting. Highlight code and click code button.

What is the relation between main class and inner classes

hi
i want to make a UML design and o want to know how to draw the relation betwwen the main public class and inner classes?
and what is the relation?

BaffyOfDaffyA wrote:
Please keep in mind that if you spell better you will get better answers and if you add duke stars you will get better answers and if you mark the thread as a question you will get better answers. That will make it look like you are paying attention and that you really want an answer.
My best answer based on your rather vague question:
A minimal public class in a file named "Minimal.java" in the directory named "minimal":
package minimal;
public class Minimal {
private int variable;
public Minimal(int var) {
variable = var;
public int getVariable() {
return variable;
}This would be an example of adding an inner class:
package minimal;
public class Minimal {
private int variable;
public Minimal(int var) {
variable = var;
public int getVariable() {
return variable;
public class Inner {
private int innerVariable;
public Inner(int var) {
innerVariable = var;
public int getInnerVariable() {
return innerVariable;
}The inner class is exactly like any other inner class except if you are accessing it from anything else other than Minimal then you would have to add Minimal. right before Inner for example, where the Minimal class could use
Inner inner = new Inner(5);other classes would have to use
Minimal.Inner inner = new Minimal.Inner(5);
See [Inner Class Example|http://java.sun.com/docs/books/tutorial/java/javaOO/innerclasses.html] or [Nested Classes|http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html] for more information.
He is probably not asking what an inner class is or how to declare one in raw source code. To me he is asking how do I
explain this relationship in a UML diagram and as UML is not and exact science and expression can vary a lot
between UML design applications I didn't want to stab in the dark.
@OP I would say whatever seems most logical to you and your team, write something that reads.

Swing - how to pass selected value out from actionPerformed() inner class?

Hi all,
I have a form with JcomboBox and textfields and I have to update the database
with the submitted values. How can I pass the comboBox value out? I cannot defined boxValue as final outside the inner class.
JComboBox list1 = new JComboBox (vector1);
list1.addActionListener ( new ActionListener() {
public void actionPerformed (ActionEvent ev) {
boxValue = (String) ((JComboBox) ev.getSource()).getSelectedItem();
thanks
andrew

OK, OK, my bad for not reading the whole post...
1. Who needs to know the current JComboBox value? If the code that needs to know has access to the JComboBox, it can just get it from there. If the code is invoking the form, it is the responsibility of the form, not the listener, to return the values to the invoker.
Please give us more information about what you are tryiug to do.

How to access super of enclosing class from inner class?

Hello,
I'd like to access Base.foo() from inner class in overridden Improved.foo(), but seem unable:
public class InnerSuper {
     public static class Base {
          protected int foo() {
               return 1;
     public static class Improved extends Base {
          @Override
          protected int foo() {
               return Integer.parseInt(new Object () {
                    public String toString() {
                         return "1"+foo() ;
               }.toString());
     public static void main(String[] args) {
          System.out.println(new Improved().foo());
}The code above does not work, as it recursively calls Improved.foo() where I'd like it to call Base.foo(). What syntax construct should I use? Improved.this would be the same thing, Improved.super does not exist.
I came up with a work around: adding a method baseFoo() to Improved and call that in the inner class:
   int baseFoo() {
      return super.foo();
   } but remain wondering if that is necessary?

Indeed, Improved.super.foo() is allowed. My Eclipse syntax highlighting seems to have the same opinion as you: "are you sure you want to write that kind of code?" and leaves the read underlining for a syntax error on for just a second longer.
This is where I am now:
     public static class DeferredExecSubroutineCall extends SubroutineCall {
          RelayExecutor relay;
          public DeferredExecSubroutineCall(RelayExecutor relay) {
               this.relay = relay;
          @Override
          protected String execute(final IFDSOC fd, final String commandText) {
               Future<String> f = relay.submit(new Callable<String>() {
                    @Override
                    public String call() throws Exception {
                         return DeferredExecSubroutineCall.super.execute(fd, commandText);
               try {
                    return f.get();
               } catch (InterruptedException e) {
                    throw new RuntimeException(e);
               } catch (ExecutionException e) {
                    if (e.getCause() instanceof RuntimeException) {
                         throw (RuntimeException) e.getCause();
                    } else {
                         throw new RuntimeException(e.getCause());
     }which is my current effort of adding concurrency to an existing project. I find it quite elegant but I am interested to hear from you...

Accessing inner classes

I am making a simple drawing program where the user can draw with the mouse on a jpanel.
i have my program structure with one big class and two inner classes
the first inner class creates the panel you can draw on and the mouselistener events to allow a user to draw.
the second class creates another jpanel that allows you to make a color with the three properties red,green and blue. it also has two buttons. one to set the forground(the color you will draw with) and the other to set the background.
I can get the forground one to work because i set the color created to a varible and sense there are mouse listners everytime the mouse listener executes it can grab that varible and set the color of the line be drawn.
my problem is with the background, i can't figure out how to access my first inner class from my second inner class to change the panels background to corspond with the user.
is there some listener i can apply or a way to change the properties of one inner classes objects from another inner class???
please help

I dont knoew if I understand your problem exactly- but if you are wanting to access the first inner class from the second inner class- you can go through the outer class like so:
public class InnerOuter {
public InnerOuter() {
public void test(String s) {
    Inner i = new Inner();
    i.setBackground(s);
class Inner{
    public String B="inner";
    public void setBackground(String s){
      //do something
class Inner2{
    public String C="inner2";
    public void setBack2(){
      InnerOuter.this.test("red");
public static void main(String[] args) {
    InnerOuter innerOuter1 = new InnerOuter();

Accessing inner Classes.. how?

I'm reading the Java API and there is an Interface class named DocumentEvent that has an inner class named DocumentEvent.ElementChange..
Since all is well with adding a DocumentListener (as per the API) for DocumentEvents, how is it possible to access the inner class' method? Do I need to implement another interface i.e. ElementChange and then write out all the methods?? What I really want is to use a method from DocumentEvent - getChange( Element elem) but this one relates to the inner class somehow.. can anyone answer this?
Thanks so much!!!

For example, in the caller
A a = new A();
(a.new B()).mm();for the method mm() in the inner class B of the class A.
class A{
class B{
void mm(){
System.out.println(Integer.MIN_VALUE);
}

Using Reflection can we find out details of inner classes in a class

Hello All,
Thanx in advance.
I intend to figure out the name of the inner class and methods declared inside it. How can this be done using reflection API's.
I need the above information to make an automated java doc creation tool for the project I am working in.
Thanx again...
VIkas

Thanx silkm,
Actually suggestion # 1 I have already tried. I used
getClasses() method which returned me a Class[] of
length = 0. i dunno Why?Because you are not using the reflection API correctly. If you read the javadocs you would know that it is structured so that all getXXX() methods return all XXX things that are public and are either declared by the target class or possibly inherited from superclasses.
As contrasted to that, getDeclaredXXX() methods can return all XXX things (including private) but only declared by the target class (not inherited).
You got an empty result back in your case most likely because all your nested/inner classes were non-public. Use getDeclaredClasses() instead.
As to suggestion # 2, the exercise I am doing is a
step before using the java doc tool. One has to insert
a javadoc comment before the method begins in order to
create a java doc. So thats it.This is independent of the reflection API but you might consider using the doclet API for this.

Help: Factory Class using Inner Class and Private Constructor?

The situation is as follows:
I want a GamesCollection class that instantiates Game objects by looking up the information needed from a database. I would like to use Game outside of GamesCollection, but only have it instantiated by GamesCollection to ensure the game actually exist. Each Game object is linked to a database record. If a Game object exist, it must also exist in the database. Game objects can never be removed from the database.
I thought about making the Game object an inner class of GamesCollection, but this means that Game class constructor is still visible outside. So what if I made Game constructor private? Well, now I can't create Game objects without a static method inside Game class (static Object factory).
Basically what I need is a constructor for the inner Game class accessible to GamesCollection, but not to the rest of the world (including packages). Is there a way to do this?

leesiulung wrote:
As a second look, I was initially confused about your first implementation, but it now makes more sense.
Let me make sure I understand this:
- the interface is needed to make the class accessible outside the outer classBetter: it is necessary to have a type that is accessible outside of GameCollection -- what else could be the return type of instance?
- the instance() method is the object factory
- the private modifier for the inner class is to prevent outside classes to instantiate this objectRight.
However, is a private inner class accessible in the outer class? Try it and see.
How does this affect private/public modifiers on inner classes?Take about five minutes and write a few tests. That should answer any questions you may have.
How do instantiate a GameImpl object? This basically goes back to the first question.Filling out the initial solution:
public interface Game {
    String method();
public class GameCollection {
    private static class GameImpl implements Game {
        public String method() {
            return "GameImpl";
    public Game instance() {
        return new GameImpl();
    public static void main(String[] args) {
        GameCollection app = new GameCollection();
        Game game = app.instance();
        System.out.println(game.method());
}Even if you were not interested in controlling game creation, defining interfaces for key concepts like Game is always going to be a good idea. Consider how you will write testing code, for example. How will you mock Game?

Problems importing a class with inner class

Why can't I import a class so that I can use an (inner) static member class without naming the enclosing class. Put simply, I have:
file C:\MyJava\Test\A:
public class A {
public static class B { }
}file C:\MyJava\Test\C
import A.*;
public class C { }When I try to compile C (javac -classpath C:\MyJava\Test;. C.java) it fails with C.java:1: package A does not exist

Class A must be in a package if you wish to import it. If you want to use the inner class, just import somepackage.A. You could then refer to A.B...
HTH :o)

Extending class + accessing base class's children

Hello.
I'm trying to create a sort of info and tool panels for a project, similar to the ones on the Adobe Suite's products. They'll have a tab that you can double click to open or close them and the panel's title will be on this tab.
So I created a MovieClip called MainPanel and inside it I placed a textfield called txtTitle and a rectangular MovieClip called mTab. I duplicated the MainPanel twice on the stage, called them PanelA and PanelB, and added individual elements to them, but kept the txtTitle and mTab. I edited PanelA and PanelB's linkage options to link them to specific custom classes.
First I created a base class for the MainPanel.
package com.panels{
    import flash.display.MovieClip;
    import flash.events.MouseEvent;
    import fl.text.TLFTextField;
    public class MyPanel extends MovieClip {
        public function MyPanel ():void {
            txtTitle.mouseEnabled = false;
            mTab.doubleClickEnabled = true;
            mTab.addEventListener(MouseEvent.DOUBLE_CLICK, clickedPanel);
And then the classes for Panel A and B, which extend the MainPanel.
package com.panels{
    import com.panels.MyPanel;
    public class PanelA extends MyPanel {
        public function PanelA ():void {
When I test the movie, I get an error saying "Access of undefined property txtTitle" (and the same for mTab). If I just link PanelA to the MainPanel class it all works - I got it to open, close, dragged it with the mouse... I can access mTab, txtTitle and anything else already on the stage. But if I extend the class, I no longer can. Does anyone know why this happens and the best way to get it to work? Thank you.

Still didn't do the trick, I even tried building a project from scratch with just the classes I mentioned in my example and nothing else, and then a second version where I have all files on the same directory. Not sure if it might have something to do with this being for an AIR app.
I have found a solution that seems to be working. My new MyPanel class:
package com.panels{
    import flash.display.MovieClip;
    import flash.events.MouseEvent;
    import fl.text.TLFTextField;
    public class MyPanel extends MovieClip {
        private var _title:TLFTextField;
        private var _tab:MovieClip;
        public function MyPanel ():void {
            _title = MovieClip(getChildByName("txtTitle")); //If I don't cast the result as a MovieClip I get an error
            _tab = TLFTextField(getChildByName("mTab")); //Same for the TLFTextField
            _title.mouseEnabled = false;
            _tab.doubleClickEnabled = true;
            _tab.addEventListener(MouseEvent.DOUBLE_CLICK, clickedPanel);
Still I'd like to understand why I need to go through these hoops so I don't make the same mistake again.

Don't understand Inner Classes and how to use it

Hi
As you guess i 'am a newbie!
I don't understand Inner Classes, particulary members(methods & fields) that an Inner method is able to manipulate.
So I know that the methods of an Inner class (respectively Outer Class) instance can access members (private or public) of an instance of the Outer Class (respectively Inner Class).
I tried to answer to a quizz : http://java.sun.com/developer/onlineTraining/new2java/supplements/quizzes/January03.html
In the following class definition, which variables are inaccessible within the method of the inner class?
class Test1 {
   public static int a = 1;
   private static int b = 2;
   public int c = 3;
   private int d = 4;
   public static class Inner {
     int e = 5;
     public void aMethod(int f) {
       int g = 6;
       // What can't be accessed here?
}A.      b, c, d
B.      c, d
C.      b, c, d, f
D.      None of them
In my opinion members (public or private) of the Outer Class can be accessed by methods of the Inner Class; e.g: a, b, c,d thus for me the answer is D.
Obviously i'm wrong, but why?

Hi
As you guess i 'am a newbie!
I don't understand Inner Classes, particulary
members(methods & fields) that an Inner method is
able to manipulate.
So I know that the methods of an Inner class
(respectively Outer Class) instance can access
members (private or public) of an instance of the
Outer Class (respectively Inner Class).
I tried to answer to a quizz :
http://java.sun.com/developer/onlineTraining/new2java/
supplements/quizzes/January03.html
In the following class definition, which variables
are inaccessible within the method of the inner
class?
class Test1 {
public static int a = 1;
private static int b = 2;
public int c = 3;
private int d = 4;
public static class Inner {
int e = 5;
public void aMethod(int f) {
int g = 6;
// What can't be accessed here?
}A.      b, c, d
B.      c, d
C.      b, c, d, f
D.      None of them
In my opinion members (public or private) of the
Outer Class can be accessed by methods of the Inner
Class; e.g: a, b, c,d thus for me the answer is
D.
Obviously i'm wrong, but why?Inner class method can access all the private members of the class. But the inner class is static. So the non-static members cannot be accessed directly (i.e. c and d).
***Annie***

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

Why are protected fields not-accessible from sub-classed inner class?

I ran across a situation at work where we have to sub-class an inner class from a third-party package. So, it looks something like this...
package SomePackage;
public class Outer {
   protected int x;
   public class Inner {
package OtherPackage;
public class NewOuter extends Outer {
   public class NewInner extends Outer.Inner {
}Now the NewInner class needs to access protected variables in the Outer class, just like the Inner class does. But because NewOut/NewInner are in a different package I get the following error message.
Variable x in class SomePackage.Outer not accessible from inner class NewOuter. NewInner.You can still access those protected variables from the NewOuter class though. So, I can write accessor methods in NewOuter for NewInner to use, but I am wondering why this is. I know that if NewOuter/NewInner are in the same package as Outer/Inner then everything works fine, but does not when they are in different packages.
I have to use JDK1.1.8 for the project so I don't know if there would be a difference in JDK1.2+, but I would think that nothing has changed. Anyway, if you know why Java disallows access as I have detailed please let me know.

Although I don't have the 1.1.8 JDK installed on my system, I was able to compile the following code with the 1.3.1_01 JDK and run it within a Java 1.1.4 environment (the JVM in the MSIE 5.5 browser). As long as you don't access any of the APIs that were introduced with 1.2+ or later, the classes generated by the JDK 1.2+ javac are compatible with the 1.1.4+ JVM.
//// D:\testing\SomePackage\Outer.java ////package SomePackage ;
public class Outer {
    protected int x ;
    public Outer(int xx) {
        x = xx ;
    public class Inner {
}//// D:\testing\OtherPackage\NewOuter.java ////package OtherPackage;
import SomePackage.* ;
public class NewOuter extends Outer {
    public NewOuter(int xx) {
        super(xx) ;
    public class NewInner extends Outer.Inner {
        public int getIt() {
            return x ;
}//// D:\testings\Test.java ////import OtherPackage.* ;
import java.awt.* ;
import java.applet.* ;
public class Test extends Applet {
    public void init () {
        initComponents ();
    private void initComponents() {
        add(new Label("x = ")) ;
        int myx = new NewOuter(3288).new NewInner().getIt() ;
        TextField xfld = new TextField() ;
        xfld.setEditable(false) ;
        xfld.setText(Integer.toString(myx)) ;
        add(xfld) ;
}//// d:\testing\build.cmd ////set classpath=.;D:\testing
cd \testing\SomePackage
javac Outer.java
cd ..\OtherPackage
javac NewOuter.java
cd ..
javac Test.java//// d:\testing\Test.html ////<HTML><HEAD></HEAD><BODY>
<APPLET CODE="Test.class" CODEBASE="." WIDTH=200 HEIGHT=100></APPLET>
</BODY></HTML>

Inner Classes doubts

Hi All,
I am trying to learn Inner classes in Java. I am referring to the book Core Java by Horstmann and Cornell.
I know that there are various types of inner classes namely:
- Nested Inner classes
- Local Inner classes
- Annonymous Inner classes
- static inner classes
First I am on with Nested Inner classes :
Following is the code which I am executing :
package com.example.innerclass;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Date;
import javax.swing.JOptionPane;
import javax.swing.Timer;
public class InnerClassTest {
      * @param args
     public static void main(String[] args) {
          // TODO Auto-generated method stub
          TalkingClock clock = new TalkingClock(1000,true);
          clock.start();
//          JOptionPane.showMessageDialog(null,"Quit Program");
//          System.exit(0);
class TalkingClock
     private int interval;
     private boolean beep;
     public TalkingClock(int interval, boolean beep){
          this.interval = interval;
          this.beep = beep;
     public void start(){
          ActionListener listener = new TimePrinter();
          Timer t = new Timer(interval,listener);
          t.start();
     private class TimePrinter implements ActionListener{
          public void actionPerformed(ActionEvent event){
               Date now = new Date();
               System.out.println("At the tone time is : "+now);
               if(beep)
                    Toolkit.getDefaultToolkit().beep();
}Following are my doubts :
1. Why do we need to give the line
JOptionPane.showMessageDialog(null,"Quit Program");
System.exit(0);without this line the program doesn't show any output.
2. I didn't understand this syntax.
You can write inner object constructor more explicitly using the syntax. :
outerObject.new InnerClass(construction parameters)
For e.g.
ActionListener listener = this.new TimePrinter();
Here the outer class reference of the newly constructed TimePrinter object is set to this reference of the method that creates the inner class object. the this. qualifier is redundant. However, it is also possible to set the outer class reference to another object by explicilty naming it. For e.g if TimePrinter were a public inner class, you could construct a TimePrinter for any talking clock.
TalkingClock jabberer = new TalkingClock(1000,true);
TalkingClock.TimePrinter listener = jabberer.new TimePrinter();
Please do help me understand this concept.
Thanks
Siddharth

I have understood that this explanation :
i) assuming that TimePrinter is an inner class of TalkingClock, that you'd need an instance of the later in order to create an instance of the former.Yes.
Being a non-static inner class, it can not be instantiated out of context ... which context is the outer class.No. See my reply 11. The "context" is an instance of the outer class - it bears repeating.
ii) jabberer is the outer instance that you are providing.Yes (more accurately it's a reference to an instance of the outer class, but that would be nit-picking).
The left side is identifying the class, the right side is identifying the instanceNo.
I'm not sure what you're calling left side and right side.
If you're talking about both sides of the equals sign, then no, it's completely wrong.
If you're talking about both sides of the "point" sign, then it's wrong too, just a bit less wrong.
Let's revise this step by step (good thought process).
1. in first line we are getting an outer class reference with this code
TalkingClock jabberer = new TalkingClock(1000,true);
this line is very natural and easily understood. Yes. The correct wording would be merely "we are getting a reference to an instance of the outer class". Sorry to insist densely.
2. Now when we come to the second line, i.e. where we try to instantiate an inner class with this line of code
TalkingClock.TimePrinter listener = jabberer.new TimePrinter();
- I do understand the concept that we need an instance of outer class in order to create an instance of inner class as inner class is visible only to outer class.No. We need an instance of the outer class as the inner class is non-static, and by definition needs an instance of the outer class. That has nothing to do with visibility (public vs private vs...). Again, some words have special meanings in the Java world.
- I also do understand that it cant be instantiated out of context. I see you like this expression, but it is too vague and misleads you. Please forget about it for a moment (no offense to otherwise helpful and knowledgeable abillconsl).
- I also do understand that left side is identifying the class and right side is identifying the instance. ANDAgain I'm afraid of which "sides" you're talking about.
- that in this line TalkingClock.TimePrinter listener = new TalkingClock().new TimePrinter();
the outer class is anonymous (new TalkingClock()) as we don't require its name here Poor choice of words again. Anonymous classes do exist in Java, but are a totally different concept, that is not related to this line.
- Also in this line TalkingClock.TimePrinter listener = jabberer.new TimePrinter();
I understood the left side part i.e. TalkingClock.TimePrinter listener =
We are attaching the outer class reference with the inner class that's absolutely understandable. Not at all!
This just declares a variable listener, whose type is TalkingClock.TimePrinter (or more accurately com.example.innerclass.TalkingClock.TimePrinter).
Then follows an assignment:
WHAT I don't understand is the right hand side, i.e., the statement jabberer.new TimePrinter();
1. I am unable to digest the fact that we can do something like anobject.new
new is an operator that is used to instantiate an instance of an object. I am unable to digest that we can do x.new?See my previous reply. This is short-hand syntax Sun chose to pass a reference to an instance of the outer class (here, jabberer) to the constructor of the inner class. They could have chosen something else. Again, bear with it.
I only know that we can do is new SomeClass(); AND NOT instance.new SomeClass();
Now you know better:
The second form is valid - only if SomeClass is a non-static inner class defined in a class of which instance is an instance.
2. Is there something to this conceptually OR this is only a syntax and that I should learn it.
I want to understand and grasp if there is some concept behind it rather than just learn and mug up. See my previous reply. Each instance of a non-static inner class stores a reference to an instance of the outer class. There must be a way (a syntax) to specify which instance (of the outer class) should be stored in the instance (of the inner class).
This particular syntax is just a syntax, the "concept" is that the instance of the inner class stores a (unmodifiable) reference to the instance of the outer class that was specified when the instance of the inner class was created.
I don't know if that deserves to be called a concept, but that's an interesting thing to keep in mind (there are some not-so-obvious implications in terms of, e.g. garbage collection).
Best regards.
J.

Outer Class Accessing Inner Classes Variables

Similar Messages

Maybe you are looking for