Inner static class implementing interface

Hello,
I have a sample program to test on reflections. here the code goes
import java.lang.reflect.*;
import java.awt.*;
import java.lang.*;
import java.io.*;
public class SampleName {
   public static void main(String[] args) {
      NewClass b = new NewClass();
       System.out.println("Calling printModifiers");
       printModifiers(b);
       System.out.println("Calling printInterfaces");
       printInterfaces(b);
   static void printModifiers(Object obj){
          Class cl = obj.getClass();
          int mod = cl.getModifiers();
          if(Modifier.isPublic(mod ))
               System.out.println("Public");
          if(Modifier.isPrivate(mod ))
               System.out.println("Private");
          if(Modifier.isFinal(mod ))
               System.out.println("Final");
          if(Modifier.isStatic(mod ))
               System.out.println("Static");
          if(Modifier.isAbstract(mod ))
               System.out.println("Abstract");
   static void printInterfaces(Object o) {
          Class c = o.getClass();
          String str = c.getName();
          System.out.println("name " +str);
          Class[] theInterfaces= c.getInterfaces();
          if(theInterfaces.length ==0)
               System.out.println("no interfaces here ");
          else
               for(int counter = 0; counter<theInterfaces.length;counter++)
                         String interfaceName = theInterfaces[counter].getName();
                         System.out.println("Interface Name :- " +interfaceName);
static class NewClass implements newInterface {
}i have an interface in t same folder as
public interface newInterface
}i get an error as below while compiling this java code
SampleName.java:54: cannot resolve symbol
symbol : class newInterface
location: class SampleName.NewClass
static class NewClass implements newInterface {
                                  ^
1 errorplease explain me what is the fault i am making and how can it be resolved.
tnx

java -cp .;<any other directories or jars> YourClassNameYou get a NoClassDefFoundError message because the JVM (Java Virtual Machine) can't find your class. The way to remedy this is to ensure that your class is included in the classpath. The example assumes that you are in the same directory as the class you're trying to run.
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Internal class implementing interface extending abstract interface :P

Confused ha? Yeah me too. RIght here it goes.
Theres an abstract interface (abstractIFace) that has for example method1() method2() and method3(). There are two other interfaces iFace1 and iFace2 that extend abstractIFace. Still with me? :P iFace1 only uses method2() whereas iFace2 uses method1(), method2() and method3(). Internal classes implementing these are then used. The reason is so that when returning an object one method can be used that will return different types of objects. But this doesnt work. It says that all the classes in the abstractIFace must be used/implemented but I only want method2() in iFace1 and all in iFace2.
Just say what the f*ck if this is too confusing cos i think it is and i did a crap job explaining!! :P

public interface IFace {
    void method1();
    void method2();
    void method3();
public class Test {
    private static class Class1 implements IFace {
        public void method1() {
            System.out.println("method1");
        public void method2() {
            System.out.println("method2");
        public void method3() {
            System.out.println("method3");
    private static class Class2 implements IFace {
        public void method1() {
            throw new UnsupportedOperationException();
        public void method2() {
            System.out.println("method2");
        public void method3() {
            throw new UnsupportedOperationException();
    public static IFace createObject(boolean flag) {
        return flag ? (IFace) new Class1() : new Class2();
}

Public class implements interface

I am taking my first crack at interfaces: I have superclass A which is a parent of class B, which implements interface C. I need to use class B to make 3 variable instances within class A. I think I will use interface C to make calculations based on the 3 variables. Where do you recommend that I declare and set values for the 3 variables if I need to output the values at the top, in superclass A?
I'm just a little unclear on pulling these objcts together... thanks in advance.

I am taking my first crack at interfaces: I have
superclass A which is a parent of class B, which
implements interface C. I need to use class B to make
3 variable instances within class A. I think I will
use interface C to make calculations based on the 3
variables. Where do you recommend that I declare and
set values for the 3 variables if I need to output the
values at the top, in superclass A?
I'm just a little unclear on pulling these objcts
together... thanks in advance. If your variables are going to be used by your superclass A then they had better be declared there. You can work with them whereever you want.
I'm not sure what you are saying about "...use interface C to make calculations based on the 3 variables." You can't do calculations inside an interface. Furthermore, if B extends A and implements C then A and C are going to be completely separate entities. Any reference to C, even if it is actually an object of type B, will not be able to use anything in A--unless you cast it to B, in which case there is no use in making an interface at all.
I probably just confused you, but oh well...
Jeff

Extend abstract class & implement interface, different return type methods

abstract class X
public abstract String method();
interface Y
public void method();
class Z extends X implements Y
// Compiler error, If I don't implement both methods
// If I implement only one method, compiler error is thrown for not
// implementing another method
// If I implement both the methods,duplicate method error is thrown by
//compiler
The same problem can occur if both methods throw different checked exceptions,or if access modifiers are different..etc
I'm preparing for SCJP, So just had this weired thought. Please let me know
if there is a way to solve this.

Nothing you can do about it except for changing the design.
Kaj

Class implementing interface using generics

I have an interface that looks like this:
public interface BinaryTree<T extends Comparable<? super T>> {
     public enum TraverseOrder { PREORDER, INORDER, POSTORDER }
     public boolean isEmpty();
     public boolean search(T key);
     public void remove ( T key ) throws TreeException;
     public void insert(T key) throws TreeException;
     public void print ( TraverseOrder order);
     public int getSize();
}My shell class that implements it looks like this:
public interface BinaryTree<T extends Comparable<? super T>> {
     public enum TraverseOrder { PREORDER, INORDER, POSTORDER }
     public boolean isEmpty(){
                  return true;
     public boolean search(T key) {
                  return true;
     public void remove ( T key ) throws TreeException {
     public void insert(T key) throws TreeException {
     public void print ( TraverseOrder order) {
     public int getSize() {
                    return 0;
}Im getting 2 errors one being
BST.java:1: > expected
public class BST implements BinaryTree<T extends Comparable<? super T>> {
and the other is an enum error. Im pretty sure the second enum error will be resolved by fixing the first error. Any help is apreciated. Thanks
BLADE

Yeah tottaly right but the code i posted is wrong sorry lets try one more time
public interface BinaryTree<T extends Comparable><? super T>> {
     public enum TraverseOrder { PREORDER, INORDER, POSTORDER }
     public boolean isEmpty();
     public boolean search(T key);
     public void remove ( T key ) throws TreeException;
     public void insert(T key) throws TreeException;
     public void print ( TraverseOrder order);
     public int getSize();
public class BST implements BinaryTree<T extends Comparable><? super T>> {
     public enum TraverseOrder { PREORDER, INORDER, POSTORDER }
     public boolean isEmpty(){
                  return true;
     public boolean search(T key) {
                  return true;
     public void remove ( T key ) throws TreeException {
     public void insert(T key) throws TreeException {
     public void print ( TraverseOrder order) {
     public int getSize() {
                    return 0;
}

Class implementation for interface

Hello,
I am a beginner in ABAP Objects.
In the coding of method if_swf_ifs_workitem_exit~event_raised of class CL_SWF_UTL_EXIT_NEW
There is the instruction follow :
*Get the workflow container
irh_container ?= im_workitem_context-> get_wf_container()
Im_workitem_context is interface type "IF_WAPI_WORKITEM_CONTEXT"
If I execute in debug mode I see the implemtation class of this interface (im_workitem_context) is "CL_SWF_RUN_WORKITEM_CONTEXT"
But where this information of implementation is defined ? (I saw nothing)
Regards
Christine
Edited by: chris_75 on Sep 7, 2010 4:22 PM

Interfaces allow to implement highly scalable object oriented applications.
Interface is a kind of a template for a real class which forces this class to implement methods defined in an interface.
The main characteristics of an interfaces are:
- they DO NOT contain any implementations (so there is nothing like INTERFACE ... IMPLEMENTATION - they have only DEFINITIONS - implementations are within classes)
- they have only PUBLIC sections.
Why we need an interface. The answer is simple:
We want to handle some objects uniformly from one application compotent, whereas these objects may behave differently inside.
Example:
Let's say we need to build a sorting program for numbers.
The program would have an interface variable L_RIF_SORTER of an interface LIF_SORTER. LIF_SORTER has a method definition SORT with an C_TAB changing parameter.
Sorting application would call the sorting algorithm as follows:
L_RIF_SORTER->SORT( CHANGING c_tab = l_tab ).
Now is the main point:
We want to have 2 kinds of sorting algorithms implemented, let's say BUBBLE SORT and QUICK SORT.
To do so, we implement 2 classes: LCL_BUBBLE_SORT and LCL_QUICK_SORT.
Both classes implement interface using the statment INTERFACES in a public section.
The user would have to choose the algorithm from an input field. Depending on the content of this field the sorting application would instantiate one class or the other using the statement:
CREATE OBJECT l_rif_sorter TYPE (variable_with_class_name).
THis is the point where ABAP gets to know the real object and its type behind the interface.
This approach is generally called the STRATEGY PATTERN. See Wikipedia for this.
I hope I answered your question.
Regards,

Can a class implements more than one interface?

Hello
Can a class implements more than one interface?
Thanks

Of course, this doesn't mean that it won't be a problem though. If the two interfaces have methods with the same signature, but different return types, you won't be able to implement them together. I.E.
interface InterfaceA {
public int doSomething(String myString);
interface InterfaceB {
public String doSomething(String myString);
// Now the classes
// Gives error "Duplicate method doSomething(String) in type ClassA"
public class ClassA implements InterfaceA, InterfaceB {
public int doSomething(String myString) {
    System.out.println("A");
    return 0;
public String doSomething(String myString) {
    System.out.println("B");
    return 0;
// Gives error "The return type is incompatible with InterfaceB.doSomething(String)"
public class ClassB implements InterfaceA, InterfaceB {
public int doSomething(String myString) {
    System.out.println("A");
    return 0;
// Gives error "The return type is incompatible with InterfaceA.doSomething(String)"
public class ClassC implements InterfaceA, InterfaceB {
public String doSomething(String myString) {
    System.out.println("B");
    return 0;
}

Implementing interface views

I have to add a main view to the portfolio items and integrate the view WI_DMS of the web dynpro component DMS_DPR to the same. When I try to do it, it says 'WI_DMS does not implement a valid interface". Is there any way to implement the valid interface dynamically? PLease help.

>i have been using ( implementing ) interfaces in the components, for example i used iwd_value_help. however i still have no clarity how WD framework is able to communicate with the component implementing interface iwd_value_help.
Web Dynpro can create a component usage based upon the interface type alone. This is very similar to normal ABAP OO when you create/get an instance of a class but only know the interface. Basically this is polymorphism at the component level.
>the basic question here is, what is wd framework, is it class implementing interfaces generated when we create views and other stuff. and this class( WD fw ) is going to call these implemented methods of the interface??
Simple answer: yes, exactly as you describe. Everything relates back to generated and local classes. The framework can interact with them becuase all the generated classes implement SAP provide framework interfaces.

Why a static class can implements a non-static interface?

public class Test {
     interface II {
          public void foo();
     static class Impl implements II {
          public void foo() {
               System.out.println("foo");
}Why a static class can implements a non-static interface?
In my mind, static members cann't "use" non-static members.

Why a static class can implements a
non-static interface?There's no such thing as a non-static member interface. They are always static even if you don't declare them as such.
An interface defines, well, a public interface to be implemented. It doesn't matter whether it is implemented by a static nested class or by an inner class (or by any class at all). It wouldn't make sense to enforce that it should be one or the other, since the difference between a static and non-static class is surely an irrelevant detail to the client code of the interface.
In my mind, static members cann't "use" non-static
members.
http://java.sun.com/docs/books/jls/third_edition/html/classes.html#246026
Member interfaces are always implicitly static. It is permitted but not required for the declaration of a member interface to explicitly list the static modifier.

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?

What is the Use of Inner classes in Interface.

Hi All,
Most of us we know that We can define inner classes in the interface. Like
public interface MyItf{
     Demo d = new Demo();
     class Demo{
          Demo(){
          //some additional code here
}Now I have following question in my mind:
1. An Interface is pure abstract. Then why inner classes inside the interface?
2. In what scenario, we can utilize these inner classes of interface?
Plz Share your views on this...
Thks for ur replies in advance.

This we cando in defining Demo Class outside.That's no argument. You could write the programs in other languages, so why use Java? Just because you can use a top-level class instead, it's no argument against using an inner class. You also can make all attributes public... you don't o that either (I hope).
Ok Also
tell me how to pass an Object in inner class Demo. to
the method of Interface.
public abstract TheInterface.Demo doSomething(TheInterface.Demo d);
Can u give some real time situation where this
concept can be used.There are only very, very few. Just because it's possible, it doesn't mean it needs to be done or is done often.

Concrete classes implement abstract class and implements the interface

I have one query..
In java collection framework, concrete classes extend the abstract classes and implement the interface. What is the reason behind extending the class and implementing the interface when the abstract class actually claims to implement that interface?
For example :
Class Vector extends AbstractList and implements List ,....
But the abstract class AbstractList implements List.. So the class Vector need not explicitly implement interface List.
So, what is the reason behind this explicit definition...?
If anybody knows please let me know..
Thanx
Rajendra.

Why do you post this question again? You already asked this once in another thread and it has been extensively debated in that thread: http://forum.java.sun.com/thread.jsp?forum=31&thread=347682

Why go for a static inner class than a regular static class

Hello,
What are the reasons to go for a static inner class? What benefits are available with a static inner class when compared to a static class?

When a class is an integral part of another class, it doesn't make sense to create a top level class for it.
Also there is no "static class" only static inner class.

Is there any statement to indentify if a class implements an interface?

Is there any statement to indentify if a class implements a particular interface?

If you want to check if a class implements an interface, look up the interface here:
http://java.sun.com/j2se/1.4.2/docs/api/index.html
and look under "All Known Subinterfaces:"
If you want to check if an object is of that interface:if(yourObject instanceof SomeInterface)
// do something
}

How can I determine at runtime if a class implements a specified interface?

subj.

isAssignableFrom(Class cls)
Determines if the class or interface represented by this Class object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specified Class parameter.

Inner static class implementing interface

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