Extending interfaces and xtending classes

Hello there,
I've extended an interface from two interfaces like this:
interface1 extends interface2, interface3
and although the compiler doesn't seem to mind, I'm not sure
whether this is really correct. With classes this is not possible
and I would need to implement multiple interfaces, but then how
would I deal with a collection of objects which I would like to
be of type interface1?
Many thanks

Here's a link that explains it in more detail:
[url
http://forum.java.sun.com/post.jsp?forum=31&thread=3800
&message=1625659&reply=true&doPost=true&subject=April
Fools:)&body=Fooled You]Interfacesoopps, should be:
[url http://forum.java.sun.com/post.jsp?forum=31&thread=38004&message=1625659&reply=true&doPost=true&subject=YoGee Fooled You:)&body=Fooled You]Interfaces

Similar Messages

Whats the difference between an INTERFACE and a CLASS?

Whats the difference between an INTERFACE and a CLASS?
Please help.
Thanx.

http://search.java.sun.com/search/java/index.jsp?col=javaforums&qp=%2Bforum%3A31&qt=Difference+between+interface+and+class

Interface and Abstract class difference

An interface can be used in such a way that we don't know the class of object assigned to a reference of that interface type until runtime. Can we use the abstract class in a similar way too?
The difference between an abstract class and interface can be listed as
1. Interface can not have implementation of any method
2. The usage of interface and class is one other difference
3. What other differences we have?

Yes an abstract class can be used in a similar way. The main issue with an abstract class is that you extend it and you can only extend one class so that can be a huge limitation that an interface does not give you.
Here's another one that is often overlooked: use both.
public abstract class SomeBaseClass implements Runnable {
public abstract void someAbstractMethod();
public void someMethodWithADefaultImplementation(){
System.out.println("Hello!");
}Any class that extends SomeBaseClass (and is not abstract) will need to implement the run() method of the Runnable interface.

Interfaces and abstract classes

can anyone pls tell me where exactly an abstract class is used and where exactly an interface is to be used.
i think the main difference between an abstract class and an interface is that an interface will have all the abstract methods whereas an abstract class can have one or more abstract methods--- if i am not wrong.
anything to add? -- pls let me know on this....
and also how they might be useful for us....

Inheritance is the most popular feature of the OOP. By organising classes into class hierachy it gives an extra dimension to the encapsulation of abstract data types becauase it enables classes to inherit attributes/methods from other classes.
There are two complementary roles of inheritance in OOP application.
1. Specialisation: Extending the functionality of an existing class.
2. Generalisation: Sharing commonality between two or more classes.
So adding functionality by extending what exists at each level to create more specialized classes. This would create a hierarchy and would be helpful even later on in maintenance.
Now when to have an abstarct class and when an interface. An interface just defines the basic functionality to be implemented by all the subclasses, though the way they are implemented may be different. e.g an interfaca animal can have all those functionalities common to all animals in basics but different in implementation. e.g all animals walk however some walk on two legs and some on four. All animals can see but they might have a different colour spectrum visible. So all such methods general but common can be in an interface.
Abstract classes come into play at a more defined level e.g in an abstract class human though walk would be the same so implemented there and then but talking can be left abstract since there may be different languages involved.
For more details refer to a good OOP book.

Interface and Inner Class

Hi,
In interface we can't provide method body.
but we can provide method body like this,
public interface TestInterface {
     public class Add {
          public int add() {
               return 100;
what is the logic behind Inner Class inside interface.
plz help.Thanks in advance.

there isn't really any logic to it, it's just something that's semantically possible. there wasn't a conscious decision to allow this, it's just a by-product of the enclosing types mechanism, and while it wouldn't be a good idea to do this, there's no technical reason why it shouldn't be possible, either

What's the most efficient way to extend product and catalog classes?

If I have additional product and catalog properties in a new database table, should
I create a new class and extend the ProductItem and Catalog classes or should
I manage these properties via the set/get property methods on the existing classes?
Is there a difference in performance with the two approaches?

Performance wise using the set/get property methods is going to be more
expensive... However, I would recommend the property approach. You really
don't want to modify or extend the provided source code. I have done this
and the approach works out fine...
Another approach that I have used is to create additional tables and classes
that key of the product and catalog classes. Again with the intension that
we don't modify provided stuff... For example, we implemented related
products using this approach.
"Bill" <[email protected]> wrote in message
news:3fbcf598$[email protected]..
>
If I have additional product and catalog properties in a new databasetable, should
I create a new class and extend the ProductItem and Catalog classes orshould
I manage these properties via the set/get property methods on the existingclasses?
Is there a difference in performance with the two approaches?

Abstract classes, Interfaces, and concrete classes

I have another technical interview tomorrow and somehow I keep getting asked the same question and I feel my answer is not really up to par. The question is:
"What is the advantage of subclassing an abstract class versus concrete class?"
"What is the difference of using an interface versus an abstract class, which is better to use?"
For the first question, I usually answer performance is the advantage because you don't have to instantiate the class.
For the second question, I usually say that you can put implementation in an abstract class and you can't in an interface. I really can't answer the second part to this question.
Any ideas?

For the first question, I usually answer performance
is the advantage because you don't have to instantiate
the class. Try invoking the class B in the following somewhere in another class.
abstract class A{
A(){
System.out.println("abstract instantiated");
class B extends A{
B(){super();}
}

Interface and abstract class

why we have constructor for abstract class and not for interface,

When you call a constructor of a class which is extended by abstract class. It runs first the abstract class constructor and then child class constructor and initialize the member variables.
while interface has no variable all final data so interface is no need to implement a constructor.
Regards,

Question about throws exception in interface and realized class

Hi,all
If I define a method In the interface like that-
public void Execute() throws NumberFormatException; In the realized class, I can define this method like that-
public void Execute() throws RuntimeException{
System.out.println("test");
}This is a right realization. But if I manage it to throws Exception or to throws Throwable in the class it leads a error. Why add this restrict only to Exception? What is the purpose of this way?
Greetings and thanks,
Jason

When you say "throws NumberFormatException" you are really saying:
When using classes implementing this interface, you have to be prepared to deal with them throwing a NumberFormatException. Other exceptions won't happen.
When you come to implement it, it might not be possible for it to throw a NumberFormatException, so there's no reason why you should have to lie about that. Code handling it directly will be fine (it doesn't throw a NFE) and code handling it via the interface will be fine (it will handle NFEs, they just don't happen).
If your concrete implementation throws other sorts of exception, such as Exception or IOException, and so on, it's incompatible with code that's manipulating the interface. The interface says "NFEs might get thrown, nothing else will." while your implementation says "IOExceptions might get thrown".
So that explains why you can't use arbitrary exceptions. The special case is RuntimeException. RuntimeExceptions don't have to be caught, and it's expected that they can happen at any time - so there's no point trying to catch and handle them as a general case.
The classic example of a RuntimeException is a NullPointerException. You don't need to declare your method as throwing a NullPointerException even though it might get thrown. And you don't have to add NullPointerException to the throws part of the interface definition, because you already know that the concrete implementation could throw a NPE at any time.
Hope that helps (a little).
I'd recommend reading the API documentation on RuntimeException and Exception to get a clearer insight into this.
Dave.

How to use interface and abstract class in the real time sennario ?

how to validate password and reenter password fields in the struts through the xml files?

Here is a modified dealForm.jsp that merges the 2 steps - both symbol submission and Yahoo convert is done by it. Play with it and add your DB code to it:
<html>
<head><title>IPIB Database Selection</title></head>
<body bgcolor="#DFDFFF">
<H1><CENTER>IPIB Database Selection</CENTER></H1>
<font size=4>
<%@ page language="java" %>
<%@ page import="java.net.*,java.io.*,java.util.*" %>
<%
String symbol = request.getParameter("symbol");
if (symbol != null) {
String urlString = "http://finance.yahoo.com/download/javasoft.beans?SYMBOLS=" + symbol + "&format=ab";
try {
URL url = new URL(urlString);
URLConnection con = url.openConnection();
InputStream is = con.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line = br.readLine();
StringTokenizer tokenizer = new StringTokenizer(line,",");
String name = tokenizer.nextToken();
name = name.substring(1, name.length()-2);
String price = tokenizer.nextToken();
price = price.substring(1, price.length()-2);
%>
<p>
Original line from yahoo <%= line %>
</p> <p>
Name: <%= name %>
</p> <p>
Price: <%= price %>
</p> <p>
Pub DB processing code from dealLoad.jsp here
</p>
<%
} catch (IOException exception) {
System.err.println("IOException: " + exception);
} else { %>
<form action="dealForm.jsp"method="GET">
<p>Enter Symbol: <input size="20" name="symbol">
<inputtype="submit" value="Submit">
</p></form>
<% } %>
</font>
</body>
</html>

JSF annotations on interface or abstract class

Hello,
Can we use JSF 2 annotations like @ManagedBeans or @SessionScoped for interfaces and abstract classes? I mean, will it works if I implement an interface which declares some annotation(s) and the managed bean class itself doesn't have annotations?
Thanks a lot!
Oleg.

Okey, an example:
@ManagedBean
public abstract class MyAbstractClass {
public class MyClass extends MyAbstractClass {
Does it work if I access MyClass by ValueExpression #{myAbstractClass} ? Will be MyClass automatically annotated with @ManagedBean?
Best regards.
Oleg.

Interfaces vs abstract classes

hi,
i have some kind of general idea about interfaces and abstract classes.but what are the situations that are most suitable for use interfaces and abstract classes..if u have any idea pls help me
thanx and best regards,
Kelum

BigDaddyLoveHandles wrote:
Reason for using interfaces #17: dynamic proxies.
import java.lang.reflect.*;
interface Fooable {
void f();
void g(int x);
class Foo implements Fooable {
public void f(){ System.out.println("Foo.f()"); }
public void g(int x){ System.out.format("Foo.g(%d)", x); }
public class ProxyExample implements InvocationHandler {
private Fooable target = new Foo();
public static void main(String[] args) {
Fooable fooable = (Fooable) Proxy.newProxyInstance(
Fooable.class.getClassLoader(),
new Class[] { Fooable.class },
new ProxyExample());
fooable.f();
fooable.g(17);
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
System.out.println("Invoking: " + method.getName());
return method.invoke(target, args);
<cat position_relative_to_pigeons="among">
Although libraries like ASM or CGLIB allow you to dynamically proxy classes, too
</cat>

I want to make gImage Class extends Image and use Graphics2D

Sorry, my english short...
I want to make gImage Class extends Image and use Graphics2D
I trying to do...
make class gImage..
extends Image class. (Inheritance)
but Image class is abstract class..
And I want to use gImage class same as Image class.
I can't use constructor... because by Abstract calss...
How do i?
Help me.. plz...
And I want to use Graphics2D at Applet Game, But not use Java JDK Plug-in...
No Way?

You need to use BufferedImage with 2D or RenderedImage with JAI.
BufferedImage effectivley extends an Image so you can
draw it to screen in paintCOmponent.
I use an Extended JPanel to draw an image in a Panel with this.
MArk

Extended receiver and enhanced interface determination

Hi,
Can somebody list me the business cases when we use the extended receiver and enhanced interface determination.In which scenarios we have to use them?
Where we can use these features and whom they can replace?
Regards,
Anoop

Hi Anoop
have alook at thses URl's also
http://help.sap.com/saphelp_nw04/helpdata/en/43/01322a7af25285e10000000a1553f7/frameset.htm
:Dynamic file and variable substitution
Similarly Extended Receiver determination is used to determine the receiver at runtime.
Refer my reply:Re: Condition In Receiver Determination Not Working
enhancement in ID
Enhanced Receiver Determination:
You use an enhanced receiver determination to have a mapping program determine the receivers of the message dynamically at runtime. Instead of creating the receivers in the receiver determination manually, you assign a mapping to the receiver determination and this returns a list of receivers at runtime.
http://help.sap.com/saphelp_nw04/helpdata/en/43/a5f2066340332de10000000a11466f/content.htm
Enhanced (Mapping-Based) Interface Determination
In an enhanced interface determination you do not enter the inbound interfaces manually, but instead first select a multi-mapping. You get the inbound interfaces from the target interfaces of the multi-mapping. The inbound interfaces are determined at runtime during the mapping step.
You typically use an enhanced interface determination if the source message has an element with occurrence 0 ... unbounded (for multiple items of a data record) and you want multiple messages (for the individual items) to be generated at runtime.
http://help.sap.com/saphelp_nw04/helpdata/en/42/ed364cf8593eebe10000000a1553f7/frameset.htm
<b>enhanced interface determination</b>
/people/robin.schroeder/blog/2006/11/15/using-dynamic-receiver-determination-with-sync-interface
/people/venkataramanan.parameswaran/blog/2006/03/17/illustration-of-enhanced-receiver-determination--sp16
List of receivers can be dyamically determined and assigned at runtime using enhanced receiver determination .
http://help.sap.com/saphelp_nw04/helpdata/en/43/a5f2066340332de10000000a11466f/content.htm
Thanks
Pls reward if useful

Track public classes, interfaces and methods by ID

Hi All,
I'm wondering whether there is a tool to assign a unique ID to classes, interfaces and methods (eg. within Javadoc) and track these IDs.
The reason I'd need such a feature is that I'd like to do requirements tracking in an easy but complete way. I have a document containing functional specifications (with IDs) and on the other side there is the source code; where the javadoc of the public methods and classes is my software specification. What I now want to do is make a link between the IDs in the functional spec to the IDs in the sofware spec (ie. the source code).
Does anybody know of such a tool (commercial or not)?
Thanks,
Daniel

I'm a bit confused as to whether or not I understand you correctly. Please tell me if the following pseudocode is somewhat like the solution you are looking for:
class MethodFunctionality {
   private Class methodClass;
   private String methodSignature;
   private List methodFunctions;
    *   Returns true if the method is used for the specified
    *   requirement, false otherwise.
   public boolean fulfills(int requirementId) {
      if methodFunctions.contains(requirementId)
         return true;
      else
         return false;
   public String getMethodSignature() {
      return this.methodSingature;
   public Class getMethodClass() {
      return this.methodClass;
    *   Returns an array with IDs of each functional
    *   requirement covered by the method.
   public int[] getCoverage() {
      return this.methodFunctions;
class ClassFunctionality {
   private Map methodDetails;
   private List classFunctions;
   public MethodFunctionality getMethodDetails(String methodSignature) {
      return (MethodFunctionality) this.methodDetails.get(methodSignature);
    *   Returns true if the class is used for the specified
    *   requirement, false otherwise.
   public boolean fulfills(int requirementId) {
      if classFunctions.contains(requirementId)
         return true;
      else
         return false;
    *   Returns an array with IDs of each functional
    *   requirement covered by the class.
   public int[] getCoverage() {
      return this.classFunctions;
}Mapping classes and methods to functionality like this would both allow you to query each class and method for all the functional requirements they claim to cover and would allow you to collect all classes and methods involved for a particular functional requirement.

Extending interfaces and xtending classes

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