Interface extending another interface

Hi, i seem to have trouble finding on the internet what happends when one interface extends another interface. Can you explain it here or give me some link where i can find such information. Thanks

have you tried to create on yet? sometimes the best way to learn is just to do it.
the truth is, extension of an interface is no different than the extension of a regular class. when you finally implement your subClassed interface, you will just have to remember to add all unImplemented methods of both interfaces. generally for soemthing like this its best to just implement multiple interfaces so that you will always know what you need to implement before run time otherwise you are bound to receive a lot of errors for not having implemented those methods.

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Interface extends another interface

Hi,
Java has the concept of inheritance for both classes and interfaces.
For classes inheritance is restricted to single inheritance. For multiple
inheritance the class should implement an interface.
But what about interfaces? Is multiple inheritance defined for interfaces?
If so, is there any documentation on this? Are there OO-design-considerations
that argue against multiple inheritance for interfaces?
Thanks for your remark or pointing to literature,
Sponiza

You should try it and see. But, not to spoil the surprise, yes Java allows an interface to extend multiple interfaces, and yes, like most everything else there are design considerations to doing this. You might wade through the long discussion here:
http://forum.java.sun.com/thread.jsp?thread=479908&forum=4&message=2241590
and hit google or search these fora
Good Luck
Lee

Calling a constructor of an object that extends another object

suppose you have the source:
class A {
public int x = 1;
public int y = 5;
public A(){y = 6;)
class B extends A {
public B(){}
public B(int a) { super(a); }
Now suppose in the main function you say
B b1 = new B();
I would think the value of x is 1 which it is, but the value of y is 6, why is this, I did not call the A constructor or does an object call the parameterless constructor of its superclass automatically. If that is the case, it will clarify to me why y gets the value of 6 and not 5.

Unless you specify a super call, it will be done. The next two constructors are the same:public B () {
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Error 1119 when class extends another class that extends movieclip

hiya
i came across this problem and i have no clue why it's happening. basically, consider 2 nested movieclips on the stage, something like stage -> main -> filler. both movieclips have instance names (main and filler).
in the library, i set main to export for actionscript, using class A:
package {
    import flash.display.MovieClip;
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it works fine. now i change it's export settings to use class B, that extends A, and it breaks:
package {
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this throws an error 1119: Access of possibly undefined property filler through a reference with static type A.
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afaik, if you dont declare super(), flash will make a call for you (but best practice is to call it always).
but i found the "solution" in another forum.
it seems that flash implicitly generates variables if you have instance names/symbols on the stage. there is an option to disable that under publish settings -> Actionscript version -> Settings -> automatically declare stage instances. by disabling that, we were able to declare public var filler:MovieClip; on class A, and that worked.
although, that solution doesnt look attractive to me. the other solution posted on another forum was to make calls to this ["filler"] instead of this.filler. that seems to work fine. i guess it has to do with the automatic variable generated thing.. who knows?
i hope that helps someone else too

When extending another class...?

I have made a BinaryTree class, tested it and everything and it all works.
Now, I have just made an AVLTree class. So, I want all the methods in the BinaryTree class to be the same as in the AVL class except the add method which I wanted to override.
So, I made the BinaryTree class abstract, and then extended the BinaryTree class in the AVL class.
So I thought that by doing this all I had to do was put in the add method and change the code and then I could use all the methods in the BinaryTree class.
Well it seems that I can, except that none of it works correctly because of private attributes. For example, my size doesn't update in my new add method and I can't figure out why. I have a private int size in both classes but it doesn't work. Not only that but my root node isn't working either.
I'll post some code here and hopefully someone knows what I'm doing wrong.
package avlTree;
* @author 383259
public class AVLTree extends BinaryTree
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      * @param left
      * @param right
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      * @param element
      * @param left
      * @param right
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private BSTNode addToTree(Comparable o)
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                    BSTNode newNode = new BSTNode(o);
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                                   currNode = currNode.getRight();
                         else if(newNode.compareTo(currNode.getElement()) == -1)
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                                   currNode.setLeft(newNode);
                                   newNode.setParent(currNode);
                                   size++;
                                   side = "left";
                                   status = true;
                                   return newNode;
                              else
                                   currNode = currNode.getLeft();
                         else
                              status = true;
                              return null;
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                    return null;
               catch (NullPointerException npe)
                    return null;
               catch (IllegalArgumentException iae)
                    return null;
     }That private, addToTree method is actually the same as the add method in the binary tree, but is only a small part of the add method in the AVLTree. Anyway, my private root node attribute and size attribute aren't updating for some reason or another, and I cannot figure out why.

So, I made the BinaryTree class abstract,And you did that why exactly?
So I thought that by doing this all I had to do was
put in the add method and change the code and then I
could use all the methods in the BinaryTree class. Which is correct. Minus the private stuff, as you found out. That's what private means, after all.
Well it seems that I can, except that none of it
works correctly because of private attributes. For
example, my size doesn't update in my new add method
and I can't figure out why. I have a private int size
in both classes but it doesn't work. Not only that
but my root node isn't working either.I guess it doesn't work because you now have two size variables and constantly use the wrong one. Make size protected, or better, provide a protected setter for the size. Do the same for other private attributes you need to access.

How does a method extend another method in the same class ??

hi everybody, I want to know if it is possible to have such code as:
void foo(){
// foo process
void bar <<extend>> foo{
//foo process
//bar process
thanks for helping me

Since you want different names for each of your so-called "child" methods, then neither overloading nor overriding in a subclass will work as each relies on the same method names. Perhaps the following will suffice:
public class MyClass
   //some stuff
   private myMethodThatDoesSomeStuff()
      //do some stuff that all the other methods must also do
   private methodA(int q, byte z)
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   private methodL(short v, float g23)
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Can extends keyword be used with respect to interfaces?

can extends keyword be used with respect to interfaces?

srinu269 wrote:
can extends keyword be used with respect to interfaces?Yes. An interface can extend another interface:
interface A {
    public void a();
interface B extends A {
    public void b();
class X implements B {
    public void b() {
    public void a() {
}

Workbench problem when interface extends interface

Hi,
I have a problem when importing an existing class into Toplink Workbench. This class has a getter/setter on a property, say getAccountType() where AccountType is an interface. This property is not persistent, only a string representation of its value stored in a private field. So as far as Toplink is concerned, the interface AccountType is not persistent.
When I try to import, I get an ExternalClassNotFoundException. We found that the interface AccountType extends another interface and this seems to be the problem. If we remove the inheritance, the import goes fine.
I don't know if this is related, but AccountType is in my project and the super-interface is in a dependency jar file (this jar file is specified in workbench's CLASSPATH).
workbench = 9.0.4.2
jdk = 1.4.2_07
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Jean-Christian Gagne

Unfortunately in 9.0.4, the error message you are receiving is not very helpful or accurate. My guess is that something the super-interface is referencing is not on your classpath and that is why you are getting the exception. In 10.1.3 this will not be a problem because we have changed how we load classes. Your super-interface would not actually be loaded in to the workbench.
Karen

Extends thread and Runnle Interface

In java there 2 ways to create thread
1.Extending thread
2.implements runnable interface
What is difference between the 2 approaches? which one to use where?

public class ThreadTest extends Thread {
public void run() {
public static void main(String[] args) {
    ThreadTest tt = new ThreadTest();
    tt.start();
public class ThreadTest extends Runnable {
public void run() {
public static void main(String[] args) {
    ThreadTest tt = new ThreadTest();
    Thread t = new Thread(tt);
    t.start();
}The difference is how you start the thread when you code it. if you extend Thread, you can call its run method directly. When you extends Runnable, A wrapper is needed to start the thread.
The Runnable approach is used when your class is extending another class (eg. JFrame). Since Java do not support multiple inheritance, you can write something like public class MyProg extends JFrame implements Runnable, and still have a thread.

Implements interface method at the derived class

Hi all.
I have a class (Derived) that extends another class (Base).
In the base class (Base) there is a method f() with its implementation.
In the interface (C) there is also f() method exactlly like in the base class (Base).
The derived class (Derived) is implements the interface (C).
My question is:
Do i have to implement the method f() in the derived class (Derived) ?

My guess is that you probably have to, even if it's just to call the parent's method.
This all sounds pretty sketchy. Why don't you just make the BASE class implement your interface?

Class constructor that implements an interface returns an "interface", why

Hi,
I am studying some code that I need to understand well. This code works, I just don't understand the following:
A class was defined extending an interface as so:
public class GeometricShape implements Area {
// constructor
public GeometricShape() {
System.out.println('bla);
In another file, GeometricShape class was instantiated as follows:
public class ExampleUse {
Area g = new GeometricShape();
My qustion is, why does the code above expects "new GeometricShape()" constructor to return an interface of type Area?
Can someone explain?
thanks

Can someone explain?When a class implements an interface, or extends another class, or when a interface extends another interface, it means that anywhere an instance of the parent class or interface is expected, the child can be used.
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If you say "give me some food," and you don't specify anything else, the person you're talking to can hand you a hamburger or an apple or a bowl of rice. Any of those will meet the requirements you put forth.
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Interface extending another interface

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