Inner question

Hi,
Inner class question:
Q.1 Given:
public class MyClass {
public class MyRunnable implements Runnable
public static void main(String [] args)
(new Thread(new MyRunner())).start();
How to rectify it? change it to (new Thread(new MyClass().new MyRunner())).start(); ??
Thanks
gogo

What error do you get?? Let me guess: something about MyRunnable being used in a static context...
You cannot instantiate a non-static inner class in a static method (main in this case), because the instance of your inner class needs a reference to the instance of the enclosing class. Solutions: (1) make class MyRunnable static, or (2) instantiate it "within" an instance of class MyClass, as you suggested yourself.
Jesper

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FACTB-------------- Dim1,Dim5,Dim6
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Inner Class Question

My question pertains to the code at the bottom of this post.
I don't understand why the compiler doesn't give an error for the line below. Why would it let you refer to something inside the class (in this case I'm referring to ClassWithInnerClass.MyInnerClass) unless it were static?
ClassWithInnerClass.MyInnerClass mic = cwic.retMyInnerClass();To illustrate why I'm asking, I created 2 ints ("regularInt" and "staticInt") inside class "ClassWithInnerClass". The compiler let me set the value of "staticInt" from within main whereas it wouldn't let me do so w/ "regularInt" (which is why I commented that line out). Don't get me wrong though - I understand the reasons why the compiler behaves as it does for "regularInt" and "staticInt". I understand that a static variable can be accessed without instantiating a class (and that there's only 1 created no matter how many classes are instantiated). I also understand that, to access a non-static variable, you need to instantiate a class. My question arises only because of trying to extend that logic to MyInnerClass.
I can already take a guess that the answer is going to be something like, "the reason it works this way is because class 'MyInnerClass' is just a declaration NOT a definiton". I guess I just want confirmation of this and, if possible, some reasoning behind this logic.
HERE'S THE CODE...
class CreateInnerClasses {
     public static void main (String args[]) {
          ClassWithInnerClass cwic = new ClassWithInnerClass();
          ClassWithInnerClass.MyInnerClass mic = cwic.retMyInnerClass();
          //ClassWithInnerClass.regularInt = 5;
          ClassWithInnerClass.staticInt = 10;
          mic.printIt();
class ClassWithInnerClass {
     public int regularInt ;
     static public int staticInt;
     class MyInnerClass {
          void printIt() {
               System.out.println("Inside ClassWithInnerClass.myInnerClass");
     MyInnerClass retMyInnerClass () {
          return new MyInnerClass();

The line    ClassWithInnerClass.MyInnerClass mic = cwic.retMyInnerClass();is accepted because the name of the inner class is ClassWithInnerClass.MyInnerClass. This has nothing to do with accessing fields even though the syntax is similar.
On the other hand, the line    SomeClassWithAnInnerClass.InnerClass ic = new SomeClassWithAnInnerClass.InnerClass();is not accepted because the nested class SomeClassWithAnInnerClass.InnerClass is not static: you must have an instance of the outer class available. The correct syntax for calling the constructor of the inner class would be    Outer.Inner instance = outerInstance.new Inner();In this case you could write:    ClassWithInnerClass.MyInnerClass mic = new SomeClassWithAnInnerClass() . new InnerClass();
    // OR:
    ClassWithInnerClass.MyInnerClass mic = cwic . new InnerClass();The Java tutorial has a pretty good explanation on nested classes:
http://java.sun.com/docs/books/tutorial/java/javaOO/nested.html
http://java.sun.com/docs/books/tutorial/java/javaOO/innerclasses.html

Inner classes question

Hi guys,
I have a question to ask - when i'm writing an inner class and i want to create a new instance from it, the Eclipse forces me to use an instance of the containing class to call new.
Is it how it's done or am i doing something wrong?
public class A
    // Some code here
    public class B
         //Some code here
}Trying to create an instance:
A a = new A();
A.B b = a.new B();

What you have defined is "non-static" inner class.A "non-static" can only be instantiated only if we create an object of outer class.True.
>
There are two ways to create "inner" class object,
1)The way you have written the codeTrue.
2)
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{    // Some code here
public void createInner()
classB b=new ClassB();
public classB
//Some code here
That code won't compile. Even if you corrected it so that it did compile, it doesn't really help in the OP's situation. Did you read the advice of Saish and Jos about why class 'B' probably shouldn't be public, anyway?

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Hello!
I'm still preparing for java cert exam and have a question. If I have Outer and Inner classes like this:
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Thanks,
Victor.

"i" doesn't have a reference. "i" is a reference. I think you are trying to express this:
import java.lang.reflect.*;
public class Outer {
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example
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Jim

<<serious memory problems>>
Probably not. But it seems wasteful to keep creating a new object just to set some properties. Why not make a single AnswerPanel, with overloaded setContents() functions?
Not that I'm a Swing expert or anything....
HTH,
Ken

Question on inner classes

I have a class that has 3 inner classes, on class read the colors and font settings, how can I pass this class to the 2 other inner classes
Here is a watered down version of code:
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Thanks for the reply
Works well for first screen, but I recall the innerClasses(1 and 2) from an actionPerformed in innerClass2 and I keep getting nullPointerError when referring to innerClass3. Each screen will have different fonts and colors, so I need it to update after each button click.
// this is inside innerClass2( it's panel with buttons )
// the next screens graphics will depend on which button is selected
public void mouseReleased(final java.awt.event.MouseEvent e) {
         layeredPane.removeAll();
          currentQuestionNumber++;
          question = questionText[currentQuestionNumber] ;
// adds a JTextPane with question
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// adds a JPanel with buttons
          layeredPane.add(new innerClass2( currentQuestionNumber, ic ), 3 );Will be tearing hair out soon
Jim

A question about non-static inner class...

hello everybody. i have a question about the non-static inner class. following is a block of codes:
i can declare and have a handle of a non-static inner class, like this : Inner0.HaveValue hv = inn.getHandle( 100 );
but why cannot i create an object of that non-static inner class by calling its constructor? like this : Inner0.HaveValue hv = Inner0.HaveValue( 100 );
is it true that "you can never CREATE an object of a non-static inner class( an object of Inner0.HaveValue ) without an object of the outer class( an object of Inner0 )"??
does the object "hv" in this program belong to the object of its outer class( that is : "inn" )? if "inn" is destroyed by the gc, can "hv" continue to exist?
thanks a lot. I am a foreigner and my english is not very pure. I hope that i have expressed my idea clearly.
// -------------- the codes -------------------
import java.util.*;
public class Inner0 {
// definition of an inner class HaveValue...
private class HaveValue {
private int itsVal;
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return itsVal;
public HaveValue( int i ) {
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// create an object of the inner class by calling this function ...
public HaveValue getHandle( int i ) {
return new HaveValue( i );
public static void main( String[] args ) {
Inner0 inn = new Inner0();
Inner0.HaveValue hv = inn.getHandle( 100 );
System.out.println( "i can create an inner class object." );
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return;
// -------------- end of the codes --------------

when you want to create an object of a non-static inner class, you have to have a reference of the enclosing class.
You can create an instance of the inner class as:
outer.inner oi = new outer().new inner();

Design question about when to use inner classes for models

This is a general design question about when to use inner classes or separate classes when dealing with table models and such. Typically I'd want to have everything related to a table within one classes, but looking at some tutorials that teach how to add a button to a table I'm finding that you have to implement quite a sophisticated tablemodel which, if nothing else, is somewhat unweildy to put as an inner class.
The tutorial I'm following in particular is this one:
http://www.devx.com/getHelpOn/10MinuteSolution/20425
I was just wondering if somebody can give me their personal opinion as to when they would place that abstracttablemodel into a separate class and when they would just have it as an inner class. I guess re-usability is one consideration, but just wanted to get some good design suggestions.

It's funny that you mention that because I was comparing how the example I linked to above creates a usable button in the table and how you implemented it in another thread where you used a ButtonColumn object. I was trying to compare both implementations, but being a newbie at this, they seemed entirely different from each other. The way I understand it with the example above is that it creates a TableRenderer which should be able to render any component object, then it sets the defaultRenderer to the default and JButton.Class' renderer to that custom renderer. I don't totally understand your design in the thread
http://forum.java.sun.com/thread.jspa?forumID=57&threadID=680674
quite yet, but it's implemented in quite a bit different way. Like I was saying the buttonClass that you created seem to be creating an object of which function I don't quite see. It looks more like a method, but I'm still trying to see how you did it, since it obviously worked.
Man adding a button to a table is much more difficult than I imagined.
Message was edited by:
deadseasquirrels

Question about inner class - help please

hi all
i have a question about the inner class. i need to create some kind of object inside a process class. the reason for the creation of object is because i need to get some values from database and store them in an array:
name, value, indexNum, flag
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for this case, i do need to create a new instance of
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Hi everyone,
I am designing an art catalog on 240 pages, size 200x280 mm, which will be perfectly bound.
I wanted to have the outer margin larger than the other margins, however, I am not sure about the inner margin size - I originally set it at 15 mm, but now I am thinking it should be larger?
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Is there a special reason for making your book just slightly smaller than A4 - your size doesn't seem to be one thing or the other.
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class A {
getName(){}
setName(){}
class B extends A{
private class innerClass extends Thread{
run(){
getName()
setName()
The problem is that calling getName from inner class will use the getName from Thread beacuse that is it's super. How do I specify the getName from class A? The setName is OK because Thread does not have a setName

The only way you could do this remove the extends A and call explicitly by creating an instance of A
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a.getName()
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Doug_99 wrote:
class A {
getName(){}
setName(){}
class B extends A{
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run(){
getName()
setName()
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select *
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"Because Oracle syntactically does not support that type of construct..." Is a correct statement, but not because "It expects only one table in UPDATE statement". The synatax for an updateable join in Oracle requires a "proper" in-line view to be updated.
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Inner classes - a general question

i'm having some difficulties understanding when to use a static inner class
and when to use a non static inner class
lets say i'm implementing a LinkedList , and i want my nodes and my iterator
implemented in inner classes .
when and why should i declare them static or non static.
thank you very much in advance.

Inner classes are never static. Nested classes can be either static or non-static; a non-static nested class is called an inner class.
Anyway, an inner class implicitly gets a reference to an object of the outer class, while a static nested class doesn't, so the decision should depend on whether or not it needs that.
An iterator would need a reference to its collection so it would be a non-static nested class. A node wouldn't so it would be a static nested class.

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