Parent Class question

I have a panel class with a slider on it .
pseudocode:
public class MyJSlider extends JPanel{
private JSlider myjslider;
private Color mycolor;
public Color getColor(){return mycolor;}
the action taken by the JSlider is to set mycolor to a new Color(r,g,b);
My question, is there away to call the class that istantiated teh MyJSlider objects paint method from the
JSlider action performed
Something like
slider_B.addChangeListener(
               new ChangeListener()
                    public void stateChanged(ChangeEvent e)
     mycolor = new Color(R,G,slider_B.getValue());
// super.paint() ????????

If it's an inner class like that, it has access to the outer class's fields and final instance variables.
You can access those methods implicitly.
But you typically don't call paint() directly, you call repaint(), which issues a call to the GUI to repaint itself. (Although maybe it's different in Swing, I don't know.)
When you post code please wrap it in [code] [/code] tags so it's easy to read.

Similar Messages

Want to find out parent class of a class without using getSuperClass

hi,
I am trying to write a code to find out the base class /interfaces of a class by its object and i dont want to use getSuperClass,getInterfaces methods.
Below is a snippet i tried but it does not work:
public class Test extends Parent{
public void disp(){
System.out.println(super.getClass().getName());
public static void main(String args[]){
Test test = new Test();
test.disp2();
this outputs the child class only does not output the parent class.
Is there any method to do so?
Thanks,
Anirudh

Ok, If it can not be done then i must not ask.
So you have answered it that it is not possible without these.Thats what i wanted to know.
Should have framed the question like is it possible?and if possible how?
Thanks
Anirudh

How can a custom class call a function in "parent" class?

Say I have an application (ultrasimplified):
public class myApp {
myClass mc;
boolean foo=false;
public static void main(String[] args) {
mc = new myClass();
public static void myFunc(boolean blah) {
foo=blah;
in a separate .java file where my questions lie:
public class myClass {
boolean bar=true;
public void myClass() {
// this is wrong, but how would I do this:
foo = bar; // foo in myApp set to true
// or how would I call "myFunc()" in myApp from this class:
myFunc(bar);
my problem is that I've created a new class that I share between two applications so I could share the code. However, I want this class I created to call a function in the application class that instanciated it. Or alternatively, I would like to set a variable in the class that instanciated myClass.
How would go about this? I've used the "this" parameter in applets to pass the parent class to an inner class, but main() in applications doesn't allow the non-static "this":
myClass my = new myClass(this);
Is there something similar I can do?

You can let MyApp implement an interface and refer to that object in MyClass:
class MyApp implements Something {
main() {
MyApp app = new MyApp();
MyClass mc = new MyClass(app);
public void foo() { }
class MyClass {
Something app;
MyClass(Something app) {
this.app = app;
app.foo();
interface Something {
public void foo();
Better yet, you can let MyApp extend an abstract class that defines foo(). Then MyApp can override the foo() method. If later on, the abstract class needs to add a bar() method then default implementation can be done in the abstract class. If you make it an interface then all implementing classes will have to be updated to implement the new method.

Accessing variables in a parent class?

Hello everyone,
I'm rather new to java, and I've been looking at the documentation a bit but am still trying to figure out just what I am looking for. I've posted an example of such before where I have two seperate files, the parent class file and the child class file. What I want to do is somehow return the instance of parent that child was created with from the below code.
public class parent {
     protected int var;
     public static void main(String[] args) {
          child chld = new child();
}Is it possible to get the same instance of parent that created the child? If so, can it be used to access or modify the variables held by parent? Or is it only possible to do this by creating methods to set or get the value of the variable?
Can someone point me to the proper term as well, so as I might check the manual as well?

Another thing I just noticed; your question does not seem to match your post's subject title. Taking that into context, it is possible to read your post very differently. Do you mean that you want to reference parent from inside of its own method, not necessarily after it has returned?
You can access an object's variables and its methods from within a method it owns. To clarify what I mean...
public class Something
    int someData = 0;
    public void someAction()
        // Something has a variable "someData" which can be accessed directly from inside of Something's own method someAction()
        someData = 5;
        System.out.println(someData);
}If you mean you want a reference to the object itself from within one of its methods, Google for the "this" keyword.
None of these have anything to do with the child object though, so I'm still a bit stumped as to what exactly you mean. Perhaps a combination of all answers received so far?
Again, you probably need to further clarify exactly what you're looking for.

How can I casting from parent class to children class

Dear,
Could someone help me to casting from parent class to children class.
I have class like this
class parent{
String name;
String id;
public String getId() {
return id;
public void setId(String id) {
this.id = id;
public String getName() {
return name;
public void setName(String name) {
this.name = name;
class children extends parent{
String address;
public String getAddress() {
return address;
public void setAddress(String address) {
this.address = address;
public children() {
public children(parent p) {
//Do init super class here
In the constructor
public children(parent p) {
//Do init super class here
I like to init super class by object p (this is instance of parent class). The way to do is using:
public children(parent p) {
super.setId(p.getId());
super.setName(p.getName());
But I don't like this, because, for example I have parent class with over 30 proberties, it take time to do like that.
There are any way to use super operation to init parent class, for example super = p;
Could you show me the way.
Thanks alot

If I understand your question correctly, you are in need of a copy constructor for you class Parent. A copy constructor behaves like this:
   Parent one = new Parent();
   one.setName("...");
   //... and all other properties of interest
   Parent two = new Parent(one);
   //Now two != one, but one.getName().equals(two.getName) for property name and all othersThe copy constructor is programmed in the Parent class, more later. Then for your child class you can use it as follows
   public class Children extends Parent {
       public Children(Parent p) {
          super(p);
   }There are at least 3 ways of programming a copy constructor:
1. Just bite the bullet: type the assignment for each field this.name = p.getName()
2. Use reflection to find all common setters/getters dynamically and assign using them
3. Use a code generator that uses 2 to give you the code for solution 1 for you to paste in.
If you find doing this a lot, there are frameworks that can do these mappings, like Dozer
(PS be carefull with Date fields, don't copy the reference but create a new and equals instance, the dirty way would be this.birthdate = new Date(p.getBirthdate.getTime()); )

How to run a function i a parent class?

Hi!
Is�t possible to run a function i parent class from the child class?
if so how to implement it?
please give an example if it�s possible.

your question is off topic !
correct forum would be: Java Programming
what you are looking for is probably 'super'. The stuff is covered by java beginner's books, e.g.
Thinking in Java
downloadable at
http://www.mindview.net/Books/TIJ/

How to track child instances in parent class

I have a **simple** design question about a good way to implement LV OO.
I have a parent class (multiple instances) with a single child class. The parent class needs to keep track of all "active" instances of the child class because some parent methods must be applied to all children. Is there a way for this to happen automatically in LV? I'm not aware of any, so I assume I will have to use some "register" and "unregister" actions for creation and destruction of child class instances. But how do I track them; where do I store the list?
It would be easiest to simply add an array of child class references to the private class data of the parent. However, LV seems to not support this due to "circular referencing". I am not familiar enough with OO, nor it's implementation in LV to know what is a good design approach to accomplish this task.
Any suggestions?

What I am trying to do:
I have one or more TCP connections that I am using. The parent class is the TCP connection. The private data for the class is a queue reference. The queue data type is a type def cluster of relevant parameters. The queue has a maximum of 1 element. The reason for this abstraction is that our applications use many TCP connections "simultaneously." As such, we want almost all of the TCP support VIs to be reentrant. This means that we need semaphore action when connection parameters are changed, and we use the queue to achieve this.
The TCP standard guarantees that each message is delivered intact, but does not guarantee message order. Sending large waveforms (or data from a continuously measuring process) requires additional work to ensure that the messages are correctly reordered on the receive end. We created an Ordered Data Stream (ODS) construct to accomplish this. That is the child class. Each TCP connection has 0 or more ODS. Each ODS inherits all the TCP settings from the parent, and can use the parent communication functions. It seems this is a textbook example of the usefulness of inheritance.
However, all good parents are able to keep track of their children. The TCP class needs to be able to track all active ODS instances on that TCP connection. We are struggling with the best method to use for the TCP class to keep track of all ODSs. Adding an array of ODS class instances to the TCP "private data" does not work, due to circular referencing between parent and child classes.
In response to trying a grandparent class:
We tried using a grandparent class. We added an array of grandparent classes, from which the TCP class inherited. The array is actually ODS instances that have been (2X) upcast from ODS to grandparent (more general class) to be stored in the TCP class data. We found that adding the array of grandparent classes to the TCP class created a VI that could not compile when we attempted to place the type def cluster ("class data") on the block diagram of a VI in the TCP class.

Can I make methods which are public in a parent class into private in a child class ?

I suspect the answer to my question is probably no, but...
I have a parent class that provides several general purpose methods, I also have a child class which is intended to provide a more specific set of methods for manipulating the data in the class. As a result, calling some of the parent's methods on the child class can provide results that I'd rather not let the users of the child class have to worry about. It seemed (from my rather naive OOP experience) that the nicest way to do this would be to make access to some of the parent's public methods be private in the child class. This doesn't seem to be trivially possible.... ?
Gavin Burnell
Condensed Matter Physics Group, University of Leeds, UK
http://www.stoner.leeds.ac.uk/

Hi Gavin,
Unfortuneately I don't think this can be done. You can use an overide VI to change the functionality of a method in a child class but it has to have the same scope and the method it overides.
Regards
Jon B
Applications Engineer
NI UK & Ireland

How to get the class name static method which exists in the parent class

Hi,
How to know the name of the class or reference to instance of the class with in the main/static method
in the below example
class AbstA
public static void main(String[] args)
System.out.println(getXXClass().getName());
public class A extends AbstA
public class B extends AbstA
on compile all the class and run of
java A
should print A as the name
java B
should print B as the name
Are there any suggestions to know the class name in the static method, which is in the parent class.
Regards,
Raja Nagendra Kumar

Well, there's a hack you can use, but if you think you need it,Could you let me the hack solution for this..
you probably have a design flaw and/or a misunderstanding about how to use Java.)May be, but my needs seems to be very genuine..of not repeat the main method contents in every inherited class..
The need we have is this
I have the test cases inheriting from common base class.
When the main method of the test class is run, it is supposed to find all other test cases, which belong to same package and subpackages and create a entire suite and run the entire suite.
In the above need of the logic we wrote in the main method could handle any class provided it knows what is the child class from which this main is called.
I applicate your inputs on a better way to design without replicating the code..
In my view getClass() should have been static as the instance it returns is one for all its instances of that class.
I know there are complications the way compiler handles static vars and methods.. May be there is a need for OO principals to advance..
Regards,
Raja Nagendra Kumar
Edited by: rajanag on Jul 26, 2009 6:03 PM

My derived class suddenly doesn't recognize the parent class

I had my assignment coded, debugged, working and ready to go. So I bring my flash drive upstairs to play around with it on my other computer. When I compile the base class it compiles fine, but now when I try to compile the derived class, and the test class with the main method, I'm coming up with errors.
They have something to do with the base class not being recognized, because I can't instantiate any objects of the class now, and i get an error when attempting to compile the derived class to the effect of "cannot find symbol; symbol: class BaseClass". i get this error throughout the derived class, from the initial declaration of the class (public class DerivedClass extends BaseClass), to any references made toward methods of the parent class.
My base class compiles with no problem, but it's like nothing else is able to "use" it. I'm not sure if it has something to do with the PC im using now, and I can't confirm this at the moment because the PC I used to write the code is down (waiting on an upgrade).
ehhh.....help.
Message was edited by:
asphaltninja
null

It's not the fault of the computer hardware.
It's not the fault of the operating system.
It's not the fault of the JDK.
So don't go rebooting or reinstalling anything. The problem is that you didn't set up things on the new computer in the same way they were set up on the old computer.
In particular the compiling problem is that the compiled version of BaseClass isn't in the classpath when you try to compile DerivedClass. I can't tell why from your description.

Reflection: how to get the name of a subclass from parent class?

Suppose I have a parent class P and two subclasses S1, and S2. There's another method which has an argument of type P. Inside this method, I want to inspect the object (of type P) passed in and print its name, such as "S1" or "S2". How do you do that? I tried Class.getSimpleName(), but "P" is returned no matter which subclass objects you have. Thanks:)

That's the same as you said last time, and I'm telling you that's not what happens when I test it:
public class Parent {
public class SubclassOne extends Parent {
public class SubclassTwo extends Parent {
public class TestGetName {
public static void main(String[] argv) {
    showNames(new SubclassOne());
    showNames(new SubclassTwo());
    showNames(new Parent());
private static void showNames(Parent p) {
    System.out.println("Name: " + p.getClass().getName());
    System.out.println("Simple name: " + p.getClass().getSimpleName());
    System.out.println("Canonical name: " + p.getClass().getCanonicalName());
}prints:
Name: SubclassOne
Simple name: SubclassOne
Canonical name: SubclassOne
Name: SubclassTwo
Simple name: SubclassTwo
Canonical name: SubclassTwo
Name: Parent
Simple name: Parent
Canonical name: ParentYou must be doing something else that you're not saying. Either that or you're expressing yourself very poorly. Why not post a simple, self-contained, compilable example of what you claim is happening?

How to access the parent class variable or object in java

Hi Gurus,
I encounter an issue when try to refer to parent class variable or object instance in java.
The issue is when the child class reside in different location from the parent class as shown below.
- ClassA and ClassB are reside in xxx.oracle.apps.inv.mo.server;
- Derived is reside in xxx.oracle.apps.inv.mo.server.test;
Let say ClassA and ClassB are the base / seeded class and can not be modified. How can i refer to the variable or object instance of ClassA and ClassB inside Derived class.
package xxx.oracle.apps.inv.mo.server;
public class ClassA {
    public int i=10;
package xxx.oracle.apps.inv.mo.server;
public class ClassB extends ClassA{
    int i=20;
package xxx.oracle.apps.inv.mo.server.test;
import xxx.oracle.apps.inv.mo.server.ClassA;
import xxx.oracle.apps.inv.mo.server.ClassB;
public class Derived extends ClassB {
    int i=30;
    public Derived() {
       System.out.println(this.i);                  // this will print 30
       System.out.println(((ClassB)this).i); // error, but this will print 20 if Derived class located in the same location as ClassB
       System.out.println(((ClassA)this).i); // error, but this will print 20 if Derived class located in the same location as ClassA
    public static void main(String[] args) {
        Derived d = new Derived();
Many thanks in advance,
Fendy

Hi ,
You cannot access the controller attribute instead create an instance of the controller class and access the attribute in the set method
OR create a static method X in the controller class and store the value in that method. and you can access the attribute by
Call method class=>X
OR if the attribute is static you can access by classname=>attribute.
Regards,
Gangadhar.S
Edited by: gangadhar rao on Mar 10, 2011 6:56 AM

How to reference the class-instance, created in parent class.

Hi, I have following scenario. During compilation I am gettting error message -- "cannot resolve symbol - symbol : Variable myZ"
CODE :
under package A.1;
     ClassZ
     Servlet1
          ClassZ myZ = new ClassZ;
under package A.2;
     Servlet2 extends Servlet1
          myZ.printHi();
How to reference the class-instance created in the parent class?

some corrections ...
under package A.1;
     ClassZ
     Servlet1
          init()
               ClassZ myZ = new ClassZ;
under package A.2;
     Servlet2 extends Servlet1
          myZ.printHi();

How to refer the parent class object from an inner class

Hi,
I have a class X, which contains an inner private class Y. Class X has a method getY which returns an object of class Y. Class Y has a method getParent. I want to return the object of parent class from this. The code is like this:
public inerface IY;
public class X {
private class Y implements IY {
public getParent {
// ... return the object of parent class which created the object of this inner class
public IY getY() {
return new Y();
Can somebody help me with this...

interface IY {
public class X {
    private class Y
        implements IY {
        private X parent;
        public Y(X x)
            parent = x;
        public X getParent()
            // ... return the object of parent class which created the object of this inner class
            return parent;
    public IY getY()
        return new Y(this);
}Filip

Create a entity object myself in a Parent class

1) I made 2 tables, a parent and a child.
2) I created entity classes out of them, and an association.
Now I want a method in the parent-class, where I create a child, belonging to the parent. How do I do that? I see no constructor, just a Create(), but what do I fill in for the attributelist, I guess the attributes :-) but how do these two objects reference to each other?
So I'm looking for something like this code in the Parent class:
public void addChild(String NameChild)
Child.create(NameChild, This)
Is this correct? Or not?
null

Are you looking for a Composition ie "Child" should be contained in a "Parent"?

Parent Class question

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