Are Java Interfaces 'free'?

From a performance point of view, are Java interfaces free?
That is, if I have:
class Foo
public void bar() { ... // some code }
}and I change it to:
interface Foo
public void bar();
class FooImpl implements Foo
public void bar() { ... // some code }
}And I call one or other of the Foos like
Foo foo // A parameter, field or local variable.
foo.bar();Does calling foo through an interface add any overhead that calling it direct in the first example not? As I understand it, all methods are 'virtual' in Java, so it should perform the same in either case.
Thanks for any of your thoughts.
Rupert

rupertlssmith wrote:
YoungWinston wrote:
The Second Rule of Program Optimization (for experts only!): Don't do it yet.
- Michael A. Jackson
Basically, don't worry about it. Worry about writing clear, correct, object-oriented code.
Wierdly enough, in the long run, that is more likely to help than anything else you can do, should (and if) you ever need to worry about optimization in the future.
WinstonThanks for the advice. I can write good clear OO code. I am now at the future and worrying about optimization, so have made it past the second rule!Then you exactly know where your bottleneck is from the profiler you've used. Did it tell you that your interfaces are the bottleneck? If so, why do you even bother to ask here?

Similar Messages

Interface-free computer screen

** not directly related to Java **
This is interesting. Imagine all the new applications. See the presentation after the short BMW ad:
http://www.ted.com/tedtalks/tedtalksplayer.cfm?key=j_han
Jeff Han is a research scientist for New York University's Courant Institute of Mathematical Sciences. Here, he demonstrates�for the first time publicly�his intuitive, "interface-free," touch-driven computer screen, which can be manipulated intuitively with the fingertips, and responds to varying levels of pressure.

** not directly related to Java **not at all related really.
but yea WOW! so let me get this right:
instead of using a stylus or wireless mouse with which in a 3 inch
range of motion I get total screen coverage I might now have the ability
to use my dirty greasy fingertips to smear up my entire display system
while having to flail my arms around to traverse the entire 2-3 feet screen display (in the demo).
Or better yet ill be forced to make the horrible compromise -
do I lay it horizontal so i can type on it or vertical so i can see it?
Its essentially a gigantic mouse pad where you use your fingers.
Itll be great to program for. Ill have to calibrate my programs so that
people with varying strengths can use it without their different
touch pressures making the program unusable.
All kidding aside though, itll be great when we are all living with those
Minority Report computers. Instead of carpal tunnel ill have the pleasure
of throwing my arms around in the air to hit invisible keys.
By the way im just playing Devils Advocate. It it pretty cool. I actual bought a small 3 inch touch screen display to program and mess around with at home a few months ago. : )

Java Interface Question.

There are classes in the Java SDK, such as the Interface:
org.w3c.dom.Document
that have factory methods in them that carry out actual operations.
But how can this be possible, because when I program an interface:
public interface test {
public void setString(String s);
It will only compile thus, with no implementation on the method signatures?
How do Java interfaces with factory methods to this?
org.w3c.dom.Node is another one. Where does the functionality/method implementation
come from?

public interface MyInterface {
     public void method1();
class MyImplementation implements MyInterface {
     public void method1(){
public class MyFactory {
     public static MyInterface createMyInterface(){
          return new MyImplementation();
public class Test{
           public static void main(String args[]){
                  MyInterface x=MyFactory.createMyInterface();
                  x..method1();
}Now can you understand this? Assume all These classes are separate classes. This is not a problem with inner classes. Before make a reply, try to understand it or post a reply as saying it is not clear rather than posting this kind of post.

Java interfaces allow us to specify limited ways in which otherwise

can anyone explain "Java interfaces allow us to specify limited ways in which otherwise dissimilar classes, from completely different parts of inheritance hierarchy, resemble one another." please?
many thanks.

An interface defines a contract which an implementing class must fulfill. As long as the implementing class is written properly, then it provides a specific, advertised behavior. There are no restrictions as to which classes may implement a given interface (in the sense that there are inheritance restrictions, such as single-inheritance, no inheritance loops, and the like). Therefore, any two arbitrary classes may implement the same interface, and therefore provide the same behavior.
For example, the Iterator interface provides the ability to loop over a collection of objects in a well-defined way. Any class which implements Iterator would be manipulable in the same way, and could therefore be said to resemble each other.

Java interface with xml communication

Hello everybody,
For a project i need to make a java interface with xml communication.
For example ; from 1 laptop I press on a java button and then i need to get a text message on the other laptop.
The java interface is already created now the xml code for communication.
I hope someone can help me how to start with the xml code.
Are there any templates that i can use?

I need to use XML for this, cause it is in the
assignment.As far as communication is concerned, it doesn't matter that you are sending XML. You can send any kind of data. So first find out how to send data, then send data which is XML.
I only want to know if its possible to send data/text
from 1 laptop (windowsxp prof) to the other laptop
(also windows xp prof).Provided the other laptop is running a server that can receive that data.
Maybe its easier if I send data to a specific IP
address?Provided there is a server running at that IP address that can receive that data. You can use an IP address to connect to a server but that has nothing to do with sending the data.
Its important that the communication between 2 system
is in XML language.XML is not a programming language. XML is a format for storing data. You can certainly send XML-formatted data between two computers.
So i hope u have a solution for my problem.The solution would be for you to learn how communication between two computers works in the real world. If you have an assignment that says you have to make communication work, surely there was something taught to you before about how to do it?

Any good article on Java Interface usage principle?

Hi All
I find Java interface is quite good concept, but some expert mentioned in some article, "Don't over use it".
Just wonderring anyone can point me to some good article on the internet on In what kind sceniaro we need use Interface, in which case we'd better not use it.
Thanks in advance.
Steven

Then how do you explain some gurus said" don't overuse interface"?I explain it thus:
(a) it doesn't actually contradict what the article says
(b) 'don't overuse interfaces' is a tautology: it doesn't actually say anything very useful.
On the other hand there's no reason why "some gurus" can't disagree with Holub. I disagree myself to a large extent. You can define your entire API as interfaces, but then you're committed to all kinds of factory methods, and provision of secret implementation classes, etc. This can get pretty tedious pretty quickly. And, somewhere or other, you must have at least one actual class, so that you can have either a static method or a constructor, so you can get hold of your initial factory, or factory builder, or factory builder factory, or factory builder factory builder, or wherever it is that you want to start.
I've used frameworks where there were four different implementation classes for the same interface. Never did find out why. Something wrong somewhere.
When you can keep your base classes stable, I don't see a reason not to use them. 'Base class fragility' is all that Holub is really complaining about, and there are lots of solutions to that, such as 'don't' for a start. Java is chock full of stable base classes.

Java Interface does not accept method that passes ArrayList...Why?

Java Interface does not accept method that passes ArrayList...Why?
for example...
public interface Interface extends java.rmi.Remote
public ArrayList getSomething(String ID) throws java.rmi.RemoteException;
Why is this not acceptable?

Java Interface does not accept method that passes ArrayList...Why?for example...
ALSO:
You are not 'passing' ArrayList, you are returning it.
If you are 'passing' anything, it is String.
~David

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Best way to learn Java. Free resources online?

Hello. I would like to start to learn Java but have no programming background except for Visual Basic and the basics of PHP. I started to learn about a week ago and now have a good understanding of some of the basic concepts, such as the IF, SWITCH, LOOPS, PRINTLN, ect. I am very interested in developing applications for the Blackberry and was wondering where I should start and what I should learn. Must I learn the entire Java programming language to start to develop mobile applications? Are there any free resources on the Sun Java website that would be able to help me learn?
Thank you
Edited by: n3xtgen on May 20, 2010 12:27 PM

n3xtgen wrote:
Must I learn the entire Java programming language to start to develop mobile applications?Depends on what you mean by "entire Java programming language". You should probably have a solid understanding of the language and concepts before attempting mobile development.
The Java language itself is the same when developing for mobile devices (except you may be forced to rely on an older version of the language). But debugging/deployment/running your code becomes more complicated as soon as you target mobile devices.
Therefore I suggest you take some time to learn "normal" Java development. It will definitely pay of in the long run.
Are there any free resources on the Sun Java website that would be able to help me learn?There are [the tutorials|http://java.sun.com/docs/books/tutorial/]. They are pretty useful.

Accessing java Interface

Hi.
Sorry for my bad english.
I'm in trouble.
I have became a complet HttpServer with a simple servlet.
My servlet doesn't contains all of the functions, what I
MUST to use.
I have to use a givven Java Interface, to communicate via rmi
between to java servers. There are givven java classes.
I can execute a server, which creates some object.
I'm interested to use these methods, or the interface.
Somebody knows, how should i to try to do this?
(I can create the JVM,
I can access a class, but not a class of this projekt. classpath seems to be correct. How Can I use a Java Interface via JNI?)
Thanks:
Peter([email protected])

post your error messages so we can see what java is telling you.

Contract-first : WSDL vs Java interface

Hello,
I am starting to work with web Service.
Many blogs and articles suggest to write WebServices contract from a WSDL.
I am a java Programmer. I totally agree with the contract-first and the data-driven communication concept.
Here is my question: why use WSDL when you can convert any Java Interface and Bean into a WebServices?
If a tool gives you the possibility to move from xml to java (and vice-versa), why not stay with a java interface?
What are the pitfalls of using this technique (other than being too easy to change the contract)?

The main reason why you would want to write WSDL first is to be able to create a more verbose XML schema. For instance, if you take a raw Java interface or class and convert from Java to WSDL/XSD everything ends up being optional because the converters have no idea what is supposed to be required versus what isn't as well as field length restrictions etc. Some of the newer tools may allow you to do this with annotations but I haven't really looked into this.
Writing the XML schema first allows you to offload more work on the XML parser at run time because it can do the schema validation for you instead of you having to manually perform this. This also allows someone writing their own client to consume the WSDL and be able to generate a client that will do more work than one based off of Java classes (e.g. someone creating a .NET client can let the XML parser do some heavy lifting during the marshalling process before ever sending the request to your web service).

(262119469) Q WSC-15 Is the .ctrl file just a java interface?

Q<WSC-15> Is the .ctrl file just a java interface?
A<WSC-15> Yes. Any control that you generate in Workshop is really an interface definition
for the methods that the enterprise component understands. You can then use those
methods in the interface directly in your .jws code. The actual object that implements
that interface and acts as a broker to the enterprise resource is generated during
the compilation of the web service. This helps keep your web service code very simple.

I don't see a way to do this. You want to transform a function to a variable. Even if that's a variable holding a function, these are incompatible.
But you can just override the function in the class instantiation:
var responder = Response {
override function doResponse(input: String): String {
return "JavaFX Rocks!"
}

Java Interface solves Deadly Diamond of Death??

I'm new to Java and am studying Head First Java, 2nd Ed. It has stated that Interfaces are Java's solution to the Deadly Diamond of Death and I'm missing something important... it could be I'm not fully understanding the Deadly Diamond of Death scenario. The book sets it up as a superclass with two subclasses that are in turn superclasses for another class with multiple inheritance - the two superclasses inherit and both override a method and the ultimate subclass can't discern between the two. My question is why can't a very similar situation develop in Java when a class inherits a method from a superclass and implements an interface specifying a method of the same name? The class has to implement the interface method - is it coincidence whether that implementation becomes an override or an overload or is illegal - it seems like I could imagine method signatures between an inherited method and the interface method of the same name that would result in each possibility. I'm obviously missing something - if anyone can shed some light on the subject I would appreciate it very much. Thanks.

BobCap wrote:
My question is why can't a very similar situation develop in Java when a class inherits a method from a superclass and implements an interface specifying a method of the same name? Is this what you are thinking of:
public class Main extends FooClass implements FooInterface {
    public static void main(String[] args) {
        new Main().foo();
class FooClass {     public void foo() { println("FooClass::foo()"); } }
interface FooInterface {   void foo(); }If not, write code to show what you are exactly talking about. If it is, I think of that possibily being a "logical" diamond issue. A little confusing and maybe not what you want. But there is no "physical" diamond problem (two methods with the same signature).
The class has to implement the interface method - is it coincidence whether that implementation becomes an override or an overload or is illegal -Diamond of death issues involve method overrides, not overloads. Run some tests to see if it is illegal.
I don't know why yet, but interfaces could have executable methods causing what I thought was a diamond problem: [diamond discussion |http://forums.sun.com/thread.jspa?threadID=5433914&messageID=10963287#10963287]

Q: Declaratively Implement a Java Interface, How?

Hi Again,
I want to be able to Declaratively Implement 'Response' in a JavaFX (very impressive stuff if I can do this!). Follow the example code below :)
Java Interface:
public interface Response {
   public String doResponse(String input);
}The JavaFX Class:
public class MyResponse extends Response {
override public-init var doResponse: function (input:String):String; //doesn't work!
}JavaFX Declarative Implementation (the goal):
var responder:MyResponse {
    doResponse: function (input:String):String {
        return "JavaFX Rocks!"
}So the above should allow whoever is creating "MyResponse" to implement the doResponse functionality of the class.
Alternatively, I can just have to do the following.....
public class MyResponse extends Response {
public-init var doResponseImpl:function (input:String):String;
public override function doResponse(input:String):String{
      return doResponseImpl(input);
}Either way works... but the alternative is not so nearly as clean :)
Thanks in advance...

I don't see a way to do this. You want to transform a function to a variable. Even if that's a variable holding a function, these are incompatible.
But you can just override the function in the class instantiation:
var responder = Response {
    override function doResponse(input: String): String {
        return "JavaFX Rocks!"
}

Java Interfaces without methods.

hi,
I am new to java... can anyone list me which are the interfaces with no methods in java.
thanks in advance...

Are you looking for marker interfaces?yes you got it... send a link..Hmmm ok then take this assignment ;). U to find these marker interfaces in Java SDK Serializable, Remote, Cloneable, EventListener, SingleThreadModel etc.
If you want a bigger list then follow the below link and search thru all the packages.
http://java.sun.com/javase/6/docs/api/
Good luck.

Are Java Interfaces 'free'?

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