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Do you use a decent IDE like Eclipse or Netbeans?
- switch line numbers on (preferences of eclipse/netbeans)
Because the exception is clearly happening in line 70 of your class SimpleTest - which I assume is a Unit Test.
- debug with a break point on ArrayIndexOutOfBoundsException.
the debugger will stop at that point automatically.
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Hi, I'm from a C++ background and I need to create a class that extends both AbstractAction and Observable, but this of course can't be done 'out of the box' using Java.
So I would appreciate from those more experienced than me as to how I can achieve this, assuming it even can be.
--
Bill
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You need to impliment interfaces rather then extend classes. A single class can only extend one super class, but you can implement as many interfaces as you like. The difficulty here is that you need to code every method:
class Top {
void doSomething() {
}
}
interface First {
void goFirst();
}
interface Last{
void goLast();
}
class Bottom
extend Top
implement First,
Second {
void doSomething() {
this.goFirst();
super.doSomething();
this.goLast();
}
void goFirst() {
}
void goLast() {
}
}
Simples!
Panic, Chaos, Destruction. My work here is done.
Drink. Get drunk. Fall over - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer
Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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Thanks for that, I'll do some reading on the matter.
--
Bill
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The "Java way" is to use interfaces to achieve (most of) multiple inheritance.
AFAIK, the "Observable/Observer" concept has been pretty much obsoleted by events and actions, so maybe you don't need to do what you can't.
Cheers,
Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
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Where do you read this? I got the Observable/Observer from the "Java - The complete reference 8th Ed. Ch 18, p541" and there is no reference to it being obsolete or as a candidate for it either.
What I want to do is create a class that extends AbstractAction and implements runnable. The actionPerformed will display a file open dialog allowing the user to select N files, these files are then stored in a File[] and the thread started when the dialog is closed to process the files. But I wanted the observable so I could 'emit' messages to the Observer (my UI) so I could say "Processing filename.ext..." as the processing can take a bit of time, hence the use of the thread and 'status message'. But of course if there is a better way of doing this then I'm all for learning.
The Events / Actions sounds sensible, are you able to give me a
link to something?
--
Bill
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 That's what I get for trying to make sense at midnight. I use "Java in a Nutshell, 5th ed". Observable/Observer are since Java 1.0 and the comment is "The Observable class and Observer interface are not commonly used. Most applications prefer the event-based notification model defined by the JavaBeans componenent framework and by the EventObject class and EventListener interface of this package. [java.util]" So I misread preference as superceding... I do remember the Event model being introduced (in Java 1.1) in response to a perceived hole in functionality.
Looks like you want to make your UI implement EventListener and have the worker thread spit out (your subclass of) EventObjects as required.
I'm sure there are plenty of examples floating around the web. (Java's like that  ) I'd start with Mr G and something like "Java EventObject".
Good hunting,
Peter
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
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Before starting any serious java tutorials its worth reading through the official beginner java tutorial: http://docs.oracle.com/javase/tutorial/index.html[^]
Read at least the "Trails Covering the Basics" paragraph and all of its subpages. Its a novice coder tutorial so you will progress with that quickly and you can gain a lot of important java-specific info from it that makes your work much easier. It worth at least a quicky reading even if you are lazy to try the examples!
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In java, multiple inheritance concept can only be accomplished through interfaces. I do it using the concept of adapter classes.
interface Dog
{
public void bark();
}
interface Cat
{
public void meow();
}
class DogCat implements Dog,Cat
{
public void bark()
{
System.out.println("Barking");
}
public void meow()
{
System.out.println("Meowww");
}
}
public class Hybrid extends DogCat
{
public static void main(String[] args)
{
Hybrid r =new Hybrid();
r.bark();
r.meow();
}
}
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Multiple inheritance for classes is however not supported by Java unfortunately. It is limited for interfaces only. Alternatively, you can use multi level inheritance that gets the same as the features of the multiple ones. Here is a simple trick that you can do to achieve this..
Let the super classes be S1,S2
class A extends S1
{
}
class B extends S2
{
}
class C
{
// write the code here by creating objects for A,B
// This could be good if S1,S2 are abstract and that
// you have implemented the abstract methods in the
// classes A,B. So you can create objects for A,B
// access methods in them (the implemented ones) and // also the normal ones.
}
Gowtham Gutha (http://java-demos.blogspot.com)
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App.java
Thread runnable1 = new Thread(new MyThreadRunnable(), "runnable1");
runnable1.setName(runnable1.getName());
runnable1.start();
MyThreadRunnable.java
public class MyThreadRunnable implements Runnable {
private String name;
public void setName(String name){
this.name=name;
}
public void run() {
System.out.println("Testing MyThreadRunnable"+" "+name);
}
}
Why does line 2 of App.java result in a 'null' for the name member of MyThreadRunnable? Is it not so that I just created a new Thread, passed a Runnable to it and gave it a name? Is it not supposed to be so that the name property should carry the value of Thread's getName()?
I don't understand.
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Simply put you are addressing the Thread method not the MyThreadRunnable method. You could change your code thus and it would work as expected:
MyThreadRunnable runnable = new MyThreadRunnable();
Thread thread = new Thread(runnable, "runnable1");
runnable.setName(thread.getName());
thread.start();
Panic, Chaos, Destruction. My work here is done.
Drink. Get drunk. Fall over - P O'H
OK, I will win to day or my name isn't Ethel Crudacre! - DD Ethel Crudacre
I cannot live by bread alone. Bacon and ketchup are needed as well. - Trollslayer
Have a bit more patience with newbies. Of course some of them act dumb - they're often *students*, for heaven's sake - Terry Pratchett
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You've already set the name to the thread in the constructor itself. Why are you again setting the same.
This works fine. It probably will not return null.
You'll need to call setName() on MyRunnable object and not on Thread object. By the way, the setName() method in MyRunnable object is not at all a name for the thread. It might be just for printing purposes. Do you want it like that only?
Remove runnable1.setName(thread.getName()), try calling the setName() method in the class that you've written (MyRunnable).
It should work! Test once.
Gowtham Gutha (http://java-demos.blogspot.com)
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I've tired to get exact ethernet ip address.
InetAddress ip=InetAddress.getLocalHost();
String iaddr = ip.getHostAddress();
It return localhost address only. I need ethernet address only..
pls help me..
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hari301 wrote: I need ethernet address only
You need to explain your problem more fully.
A TCP connection consists for two ends AND of the connections in between.
The fact that two ends connect does NOT mean that meaningful (non-private ip) is available on either end.
The fact that two ends connect does NOT mean that one end can recover a meaningful ip for the other end in such a way that it uniquely identifies the other end.
And of course connections have nothing to do with domain names.
Now some of the above might have something to do with your problem. Or not. But it isn't clear what you think you want (neither here nor your other post.)
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Hi,
i want to create a webservice in JAVA...pls share the code.....
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This sort of question is impossible to answer in a technical forum. If you want to create a web service then you need to do some research into the tools that are available to help you. A search with Google will get you started.
One of these days I'm going to think of a really clever signature.
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Please at least try to type "Java Webservice Tutorial" @ Google.
It's so easy that I don't even want to post links here - would be a waste to web space.
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I have a bitmap, such as lena.bmp, which the number of bits per pixel is 8. How can I change the number of bits per pixel?
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Consider the following code:
public class MyThread extends Thread {
@Override
public void run(){
System.out.println("Testing thread.");
}
}
public class App
{
public static void main( String[] args )
{
MyThread thread = new Thread();
}
}
Why does the syntax checker not accept line 5 in 'App.java' (The one with the MyThread Reference Type)? If MyThread is aThread, then why is it incorrect to create a new Thread out of it? I know I'm supposed to replace it with new MyThread, but why is Thread not allowed? Doesn't 'extend' mean 'inherits all properties etc.'?
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CsTreval wrote: If MyThread is aThread, then why is it incorrect to create a new Thread
out of it?
Your code is stating that 'Thread' is a 'MyThread' which it isn't.
The correct code would be..
Thread thread = new MyThread();
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You should be creating the same type as you have declared thus:
MyThread thread = new MyThread();
One of these days I'm going to think of a really clever signature.
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Yes, but there is also polymorphism as jschell said: Thread thread = new MyThread. I just got the assignment backwards. To me it is more logical to think of a=b instead b=a.
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Thread thread = new MyThread();
...works, cause Thread is the parental to MyThread.
Using that leaves you with the basic functionality that is given in Thread (unless you cast Thread to a MyThread, then you'll be able to access the additional functions).
You could add additional functionality to any Object when you extend it - which is the basic meaning of extension.
So when initializing the Object you will have to choose the right one - the parental Object does not own the additional methods, does not know them.
You would not be able to access them.
Example:
public class Vehicle{
}
public class Bus extends Vehicle{
public int getSeatQuantity(){
}
}
A vehicle can be anything from a bike up to a race car, truck, even a train.
It's not important for a bicycle or a race car how many seats it has. But it's important for a bus.
So when you want a Bus (...and later probably know how much seats are available) you will have to create a Bus and not just a Vehicle.
Simple said: it's more specific.
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