Love this java language

I am a software engineer with mosly C background and a
lot of experience in real-time software development. I
wanted to learn Object Oriented programming and
started learning java, mostly because of free tools
and good tutorials on this site.
I love this Object Oriented programming. The Swing was
a little harder to learn, but the code generation in
the SUN ONE IDE helped me a lot to understand how it
works. The java tutorial is wonderful.
I have two problems with the language;
One these MouseListeners and Actionlisteners are hard
to work with. If you set a handler for each button
etc, it is easy. But with 100 buttons on a JFrame, the
code becomes stupid. I used getSource() to get the
Object, but the compiler doesnt know the type of the
Object, so it wont let me use any methods. So I got to
test for equality with each button, to find out which
button clicked, so I can call the proper Class
methods. This is not a good language feature, at least
I could not figure a way to do it. The language should
have a kid of a switch statement based on the class of
the Object, whchich allows you to select the right
handler from a set of classes. I am sure the run time
can figure out what the Class of the Object is. It is
just that the compiler would let you invoke the right
methods.100 buttons? That doesn't sound like a good GUI design to me. Anyway, this is problem most people encounter at one point or another. Using listeners are a pattern based on the Observer - Observable pattern. Patterns are the next step after OO. I suggest you read up on them. In particular, I would read the MVC pattern. This will give you an idea of how to eliminate this bad practice.
The other problem I had was it would not let me use
local variables in the constructor of an anonymous
Class. I just couldnt understand what the rational for
that is?You can use local varaibles in anonymous inner classes but only if they are final. The rational is, I suppose, to avoid unexpected behavior if the local varaible changes during the lifetime of the anonymous class instance. I don't know what the official reason is. I don't think that it isn't theoretically possible to do it, though there maybe an issue with the VM that makes this neccesary.

Similar Messages

How to convert a sql query to a java language?

A sql like this:"update myoracletable set name='myname',age=26,sex='female',address=NULL,visittime=SYSDATE,visitnum=visitnum+1where name='name' and address='address'",I want to use java language update such as :rs.updateString(),rs.updateDate() but not a sql update.How can I do in this case?

Something like this?
try{
     DriverManager.registerDriver(new oracle.jdbc.driver.OracleDriver());
     Connection con = DriverManager.getConnection("jdbc:oracle:thin:@your_server:1521:sid","scott","tiger");
     Statement st = con.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE,ResultSet.CONCUR_UPDATABLE);
     ResultSet rs = st.executeQuery("SELECT deptno,dname,loc FROM dept where deptno=28");
     while(rs.next() ) {
          rs.updateString(2,"Some Name");
          rs.updateString(3,"Some Location");
          rs.updateRow();
          System.out.println(rs.getString(1)+" : "+rs.getString(2)+" : "+rs.getString(3));
} catch (Exception e) {
     System.out.println(e);
}Sudha

I know c,c++ and java language ! and i want to contribute for development of mozilla products ! any idea where i can find beginner level projects ?

I know c,c++ and java language ! and i want to contribute for development of mozilla products ! any idea where i can find beginner level projects ! so that i can hone some real development skills too :)

You could also try jumping in on some of the Mozilla IRC chat channels as was suggested to someone else in another thread.
Also you could also try the [/forums/buddies new contributors forum], it does now have an Admin monitoring and replying. (At the time of the quoted post Admins were almost impossible to get hold of for forum matters )
''Noah_SUMO [/forums/buddies/710569#post-61671 said]''
<blockquote>
Sorry I didn't see this earlier. :)
I know just the places where I think you'd fit in best. To make sure, just join us in #sumodev and #mozwebqa and #communityit at irc://irc.mozilla.org
I think your skills in php, javascript, python and server admin-y stuff will come in real handy at these places. :D
For example, some help is needed here to fix these tests after a new theme was added to wiki.mozilla.org and they are in python. https://github.com/mozilla/wiki-tests - more info in #mozwebqa
And maybe some help with perl might be needed with firebot, a irc bot written in perl. Channel #firebot for that.
And #communityit (for server admin stuff) and #sumodev could use some help as well, just pop in and ask. :)
</blockquote>
Also see
* [[Contributor News & Resources#w_communication-channels]]_communication-channels
** Mibbit link (this one for #sumo channel ) https://www.mibbit.com/?server=irc.mozilla.org&channel=%23sumo
P.S. and see
* https://wiki.mozilla.org/Good_first_bug

Logic for user defined function in java language.

Hi Guys,
I want to use a "&" function in below code & include vafrdate.substring(130,132).equals("01").
if ( delperiod.substring(4,6).equals("01") )
Need your help to include & function in java code.
In layman language , i need,
if ( delperiod.substring(4,6).equals("01") & (vafrdate.substring(130,132).equals("01"))
pls help me to do it in java language.

Santosh,
Use this -
if ( delperiod.substring(4,6).equals("01") && vafrdate.substring(130,132).equals("01"))
Regards,
Neetesh

Some changes we need in the Java language

Dear Java language makers,
I'm actually coding a fairly complex program, and I'm facing several issues c++ does solve while Java doesn't handle them. I strongly wish these features could be included in next editions of the Java language, and I think I'm not the only one...
1) Friend Class access
Say I have a parser and a Data structure. The parser reads a file, and updates another class (being a data structure) as it parses line by line an input text file.
I want my parser to fill up the data structure step by step, that is field after field, rather than using a constructor, because the information appears sequentialy in my text input file.
Using a constructor to intitialize my data structure (rather than field by field access on a void object)would require me creating several variables in my parser for buffering the information, then create my object. This results in a loss of coding performance, and execution performance (spending time allocating and killing buffer values).
On the other hand, I don't want these field values to be exposed to the users of my SDK, I want them to be accessed thru accessor methods.
You would answer me : put both classes in the same package, and declare the fields of the data structure "protected", and accessors "public".
Yes, that is a solution...but if you do really think Object Oriented, this sucks. Because a data structure and a parser are not the same thing, and I want to have them in separate packages.
one being named myApp.Datasets, the other being named myApp.Parsers.
And this can't be done with Java.
If only I could declare in my data structure class the Parser class as a Friend Class, this would solve the issue and be CLEAN for Object Oriented programming !
2) Operators
This very annoying the Java language doesn't support operators
Say you have a Vector3D class and you want to make a calculation :
in c++, you can define operators for your class, and make a calculation like this :
float a;
Vector3D v1,v2,v3;
//calculation
v1 = v2 - v3 * a; //clean and easy to read
Now in Java, not having operators, you have to deal with functions :
float a;
Vector3D v1,v2,v3, tmpv;
v1=new Vector3D();
tmpv=new Vector3D();
//calculation
tmpv.sub(v2,v3);
tmpv.mul(a);
v1=tmpv; //dirty and unreadable
In Java you get 3 lines for a basic calculation. This is the way it's implemented in JAVA3D, and this is the best you can do in Java to my opinion.
Just imagine how math code looks in java when you code a 3D Physics engine, regarding the previous exemple, and having to deal with matrices, vectors, quaternions...Well I give you a taste, a simple slice of the code :
vtmp.cross(Airplane.vAngularVelocity,Element.vCGCoords); // rotational part
vLocalVelocity = add(Airplane.vVelocityBody , vtmp);
fLocalSpeed = magnitude(vLocalVelocity);
if(fLocalSpeed > 1) vDragVector = div(negate(vLocalVelocity),fLocalSpeed);
Vector3f v = new Vector3f();
v.cross(vDragVector,Element[i].vNormal);
vLiftVector.cross(v,vDragVector);
tmp = magnitude(vLiftVector);
vLiftVector=normalize(vLiftVector);
v=new Vector3f(vDragVector);
tmp = v.dot(Element[i].vNormal);
Got it ? :)

Because a data structure and a parser are not the same thing,
and I want to have them in separate packages.Because a data structure and a parser are not the same thing, you should not jave them as the same type (class or interface), that is right. But this does not prevent us from putting them into the same package!
java. lang.Integer and java.lang.String are not the same thing, but I am quite happy with them as classes in the same package.
Put both classes in the same package, and declare the fields
of the data structure "protected", and accessors "public".Protected access would allow access for inheriting classes as well. The default (package-wide) access would be better.

Can you write javac in java Language

Hi,
is it possible to write java compiler in java language.

Here's a compiler written in Java, it is part of an IDE I wrote:
Compiler.java: import java.io.*;
* Wrap up javac.
* The class exists to supply a single method - to compile a file
* and report status along with error/success messages
* Compilation (by javac) is carried out asynchronously using a
* background Thread. Status and any error messages are passed back to
* the calling object through a callback method.
public class Compiler implements Runnable
    * Constructor.
    * @param owner the <TT>JavacTool</TT> that has created this Compiler
   public Compiler( CompilerListener owner )
      myOwner = owner;
   private CompilerListener myOwner;
    * Compile a file using javac.
    * This method will compile a Java source file and report both the
    * status of the operation and any error strings produced.
    * The method kicks off a separate Thread that actually carries out
    * the compilation. Upon completion a the JavacTool is called back with
    * a CompilerStatus object.
    * @param filename   the name of a file which <I>must</I> be in the same directory
    * as the JavacTool was run from. this tool does not have tha capability
    * of working across multiple directories.
   public void compile( String fileToCompile )
      filename = fileToCompile;
      new Thread( this ).start();
   private String filename;
    * The method run by the separate Thread.
    * It runs once for each filename passed to the Compiler object.
    * It creates a new OS process to run "javac filename" externally
    * and captures the error output from the real compiler into
    * a String so that it can be returned to the calling code via
    * a callback method (very similar in principle to an event)
   public void run()
      CompilerStatus returnValue = new CompilerStatus();
      returnValue.outputString = new String();
      try
         Runtime r = Runtime.getRuntime();
         Process p = r.exec( "javac " + filename );
         InputStream is = p.getErrorStream();
         BufferedReader rdr = new BufferedReader( new InputStreamReader( is ) );
         String line = rdr.readLine();
         while( line != null )
           returnValue.outputString += (line + "\n");
           line = rdr.readLine();
         p.waitFor();
         returnValue.exitValue = p.exitValue();
         if( returnValue.exitValue == 0 )
           returnValue.outputString = "Compilation successful\n\nNo errors\n";
      catch( Exception e )
        e.printStackTrace();
      myOwner.compileComplete( returnValue );
} CompilerStatus.java: public class CompilerStatus
   public int exitValue;
   public String outputString;
}JavacTool.java: import java.util.*;
import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
* The main class in the application
* Provides the screen presence for the controllers and the output view
public class JavacTool extends JTextArea implements CompilerListener
    * Constructor for the tool
    * @param list A java.util.Vector containing the list of files for compilation
    * or null if none entered.
   public JavacTool( JTextArea jTextArea )
      // View
      outputWindow = jTextArea;
      outputWindow.setFont( new Font( "Monospaced", Font.PLAIN, 12 ) );
      outputWindow.setText( "TBJava IDE: -ready to compile" );
      // Get it going!
      // Must create a Compiler object and provide it with a link
      // so that it can call this object back when it has completed
      theCompiler = new Compiler( this );
      // set the size and the visibility
      setSize( 500, 250 );
      setVisible( true );
     public void Compile( String fileToCompile )
            // Infrom user that something is happening
               filename = fileToCompile;
               outputWindow.setBackground( Color.white );
               outputWindow.setText( "Compiling " + filename );
               setCursor( new Cursor( Cursor.WAIT_CURSOR ) );
               theCompiler.compile( fileToCompile );
            // When compilation is complete, the Compiler
            // object will callback on the method compileComplete
            // The Compiler runs its own Thread so this method
            // will complete immediately and the outputWindow
            // update can occur.
   private String filename;                                             // the filename as a String
   private JTextArea outputWindow;                                   // the window containing the messages
   private Compiler theCompiler;                                        // the compiler
    * Method called by the Compiler when it has completed
    * @param status A CompilerStatus object that contains
    *    the exit value from the compiler
    *    (indicating success or failure) value == 0 => OK and value != 0 => error
    *    and an appropriate text message
   public void compileComplete( CompilerStatus status )
      setCursor( new Cursor( Cursor.DEFAULT_CURSOR ) );
      if( status.exitValue == 0 )
         outputWindow.setBackground( new Color( 0.85F, 1.0F, 0.85F ) );
                                     // pale green
      else
         outputWindow.setBackground( new Color( 1.0F, 0.85F, 0.85F ) );
                                     // pale red
      outputWindow.setText( status.outputString );
}This is taken straight from my IDE; you'll have to adapt it slightly to make it into a seperate application

Java language enhancement for method and field

similar to the way FooClass.class works in the language, i would like to see the following code constructs also supported by the java language:
[FooClass.]someMethod.method
[FooClass.]someField.field
i thought i had read that something like this was coming in se 7, but i can't seem to find the "what's new in se 7" page. can anyone direct me to it?
shackman01

I haven't read anything about that, at all. but I hope it comes to be

Java language unsatisfied link error how to fix

i get a "java language unsatisfied link error" when trying to get my Weatherlink application to run on my new iMac. It ran OK on my old one. Whats up with this?

Java for OS X 2014-001

Super class for java Language

which is the super class for java Language...
this is an interview question .
I SAY Object is the super class for java Language ...
then he asked whether object class will extend ??
i say Yes it will implectly extend ...
then he whether each and every class will extend object
i say yes ...
then he asked multiple inheritance is possible in java ...
i say no ...
then how will say object class will extend in each and every class....
hai friends if there is any solution tell mem
by
dhana

which is the super class for java Language...
this is an interview question .
I SAY Object is the super class for java Language
ge ...If you mean the ultimate parent of all classes, yes.
(Although it's not the parent of interfaces.)
then he asked whether object class will extend ??
i say Yes it will implectly extend ...Not sure what is meant by "will object extend."
then he whether each and every class will extend
object
i say yes ...Correct.
then he asked multiple inheritance is possible in
java ...
i say no ...Correct. At least in the usual sense. When people talk about multiple inheritance, the usually mean multiple inheritance of implementation, such as C++ supports. The ability to implement more than one interface in Java is sometimes referred to as multiple inheritance of interface. I don't know if that term is in common use outside of Java.
then how will say object class will extend in each
and every class....
hai friends if there is any solution tell memMultiple inheritance means that a class' ancestors are not all in a straight line to the ultimate parent. That is, not all ancestors are parents or children of each other.
You are you father's son, and he is his father's son, and so on. So your grandfather is your ancestor, and so is your father. This is not MI.
You also have a mother. She's neither an ancestor nor a descendant of your father. That's MI.

Java Language problem: Multiple interfaces extension.

Not just any interfaces. Take a close look:
public interface interface1 {
public void aMethod();
public interface Interface2 {
public void aMethod() throws Exception();
}As you can see, both interfaces define a single method with the same signature... but one of them throws Exception.
Consider "merging" these two interfaces:
public interface Interface3 extends Interface1, Interface2 {}Should the resulting method throw Exception? Eclipse says it does. But I think it shouldn't. Here's the logic:
If the method in Interface3 DIDN'T throw Exception, it would be able to extends the method in Interface1 and Interface2, because it is not throwing checked exceptions not thrown in the superinterfaces' methods definitions... however, as It DOES throw Exception, it can't extend the method in Interface1, because Interface1's method doesn't throw Exception. Am I right?

It's not a naming problem. I'll tell you where the problem comes from:
I'm working with EJBs. I (personally) like to separete the business "signatures" of the beans in a single interface.
So, for every bean I make, I have a single interface that defines the method.... it says NOTHING about the beans.
Remote beans methods have to throw RemoteException, so I have to throw RemoteException in my business logic classes. I then make two interfaces that implement this interface. One remote (that just extends this interface and EJBRemote) and another local that extends EJBLocal and overrides all the methods so they don't throw RemoteExceptions (Local bean interfaces' methods must NOT throw RemoteException).
For example:
public interface Beaninterface {
public void aMethod() throws RemoteExeption();
public interface Bean extends EJBRemote, BeanInterface {}
public interface BeanLocal extends EJBLocalObject , Beaninterface {
public void aMethod();
}No problem so far.
Here's where the mess comences:
I want to EXTEND this bean interfaces so I make a bean based on the former.
I will add another method to the business interface of the new bean:
Business Interface
public interface ExtendedBeanInterface extends BeanInterface {
public void newMethod() throws RemoteException;
}This new interface defines the new method and inherits the method from BeanInterface
Remote Interface of the new bean:
public interface ExtendedBean extends ExtendedBeanInterface, EJBObject {}Nothing wo do there.
Here is the real problem:
I have to extend the ExtendedBeanInterface, but that will bring two methods that throw Remote Exception. I have no problem overriding both methods in this interface.. but how about if thyere are 50 methods in the BeanInterface? I'm not going to go ahead and removing each method for evety bean I extend. That makes NO sense. What I think I should do is to extend BeanLocal so those methods that were brought from BeanInterface be known not to throw RemoteExeption.
public interface ExtendedBeanLocal extends EJBLocalObject, ExtendedBeanInterface, BeanLocal {
public void newMethod();
}And THERE is where I hit the wall, because when I deploy the bean, the application server informs me that the resulting interface is throwing RemoteException (courtesy of ExtendedBeanInterface).
Accoring to my logic about Java Language, by extending BeanLocal, aMethod() shouldn't throw RemoteException as a result in ExtendedBeanLocal.
So... what is the next step? Go with JCP?

Dynamic equivalent of the Java language CAST operator

Hello,
Here is what I want to do:
I have an Object that contain "something" (I don't know at compilation time). And I want to do this call:
Object myObject = new String("Hello");
myMethod (myObject);
having declared these:
public void myMethod (Integer dInt);
public void myMethod (String sString);
I want the second method to be called. How can I do that?
I'm looking for something like a dynamic equivalent of the Java language cast operator:
??? myMethod ( (myObject.getClass())myObject ); ???
or ?? myMethod ( (myObject.castTo(myObject.getClass()) ) ; ??
Thanks.

How 'bout using the instanceof operator?
Like this:
public myMethod(Object obj)
if (obj instanceof String)
//do String stuff
else if (obj instanceof Integer)
//do Integer stuff
}

Install Error: "Invocation of this Java Application has caused an InvocationTargetException"

Hi
I am installing Weblogic v 6.0 sp2 on Sun Solaris 8 on executing the command "
sh weblogic600sp2_sol.bin -i console" the installation starts and after selecting
the language as English, console displays the following error and the installation
stops, please advice
"Invocation of this Java Application has caused an InvocationTargetException.
This application will now exit. (LAX)
Stack Trace:
java.lang.NullPointerException
at java.util.StringTokenizer.<init>(StringTokenizer.java:122)
at java.util.StringTokenizer.<init>(StringTokenizer.java:138)
at com.zerog.ia.installer.steps.ChooseJavaVM.j([DashoPro-V1.2-120198])
at com.zerog.ia.installer.steps.ChooseJavaVM.c([DashoPro-V1.2-120198])
at com.zerog.ia.installer.Main.a([DashoPro-V1.2-120198])
at com.zerog.ia.installer.Main.main([DashoPro-V1.2-120198])
at java.lang.reflect.Method.invoke(Native Method)
at com.zerog.lax.LAX.launch([DashoPro-V1.2-120198])
at com.zerog.lax.LAX.main([DashoPro-V1.2-120198])
GUI-"
Has someone faced similar problem before? I have also tried installing the WebLogic
Server 6.1 as well but I get the same error.
Thanks and Regards
Kapil Singh Pawar

Hi.
What jdk version is currently installed on your solaris 8 machine? If it is not
already a 1.3.x version I suggest you install that first and put the bin directory in
your path. You might also check with Sun to see if there are any relevant OS patches
required by your jdk (or jdk 1.3.1) in order to run.
Regards,
Michael
Kapil Pawar wrote:
Hi
I am installing Weblogic v 6.0 sp2 on Sun Solaris 8 on executing the command "
sh weblogic600sp2_sol.bin -i console" the installation starts and after selecting
the language as English, console displays the following error and the installation
stops, please advice
"Invocation of this Java Application has caused an InvocationTargetException.
This application will now exit. (LAX)
Stack Trace:
java.lang.NullPointerException
at java.util.StringTokenizer.<init>(StringTokenizer.java:122)
at java.util.StringTokenizer.<init>(StringTokenizer.java:138)
at com.zerog.ia.installer.steps.ChooseJavaVM.j([DashoPro-V1.2-120198])
at com.zerog.ia.installer.steps.ChooseJavaVM.c([DashoPro-V1.2-120198])
at com.zerog.ia.installer.Main.a([DashoPro-V1.2-120198])
at com.zerog.ia.installer.Main.main([DashoPro-V1.2-120198])
at java.lang.reflect.Method.invoke(Native Method)
at com.zerog.lax.LAX.launch([DashoPro-V1.2-120198])
at com.zerog.lax.LAX.main([DashoPro-V1.2-120198])
GUI-"
Has someone faced similar problem before? I have also tried installing the WebLogic
Server 6.1 as well but I get the same error.
Thanks and Regards
Kapil Singh Pawar--
Michael Young
Developer Relations Engineer
BEA Support

How to start learning java language?

can any one advise me how to start with

can any one advise me how to start withJVerd's post is great.
Also there are some links I have compiled over the last few months along with others in this forum.
Free Tutorials and Such
Installation Notes - JDK 5.0 Microsoft Windows (32-bit)
Your First Cup of Java
The Java? Tutorial - A practical guide for programmers
New to Java Center
Java Programming Notes - Fred Swartz
How To Think Like A Computer Scientist
Introduction to Computer science using Java
The Java Developers Almanac 1.4
Object-Oriented Programming Concepts
Object-oriented language basics
Don't Fear the OOP
Free Java Books
Thinking in Java, by Bruce Eckel (Free online)
Core Servlet Programming, by Merty Hall (Free Online)
More Servlets, by Marty Hall (Free Online)
A Java GUI Programmer's Primer
Data Structures and Algorithms
with Object-Oriented Design Patterns in Java, by Bruno R. Preiss
Introduction to Programming Using Java, by David J. Eck
Advanced Programming for the Java 2 Platform
The Java Language Specification
Books:
Head First Java, by Bert Bates and Kathy Sierra
Core Java, by Cay Horstmann and Gary Cornell
Effective Java, by Joshua Bloch
Also if you are in school, definatly take a intro to programming course.
Have Fun,
JJ

Java Language Specification error reports

Well, I wanted to report a typo in The Java Language Specification, Third Edition (http://java.sun.com/docs/books/jls/download/langspec-3.0.pdf), so from http://java.sun.com/docs/books/jls/ I clicked on the "feedback form" link (which points at http://developers.sun.com/contact/feedback.jsp?&category=doc&mailsubject=Java%20Language%20Specification%20Feedback). This was redirected to http://www.oracle.com/technetwork/community/join/overview/index.html which offers no such feedback form. Consider this sort-of-broken link as the first problem I'm reporting.
The second problem is in the aforementioned pdf, section 4.8 (Raw Types), page 58, where on can read:
"The type of the member(s) of Inner depends on the type parameter of Outer. If Outer is raw, Inner must be treated as raw as well, as their is no valid binding for T."
This should be instead:
"The type of the member(s) of Inner depends on the type parameter of Outer. If Outer is raw, Inner must be treated as raw as well, as there is no valid binding for T."
I think a forum category should be created for just this: error reports about the documentation (pdfs, APIs, support web pages).
Edited by: Urhixidur on 2011-09-08 09:23

Your intentions are admirable, but you are probably wasting your time. This is a forum for Java development related questions and 99.5% of the visitors are not related to Oracle at all. most likely nothing will be done with your information.
I think a forum category should be created for just this: error reports about the documentation (pdfs, APIs, support web pages).It is a good idea actually, but such a thing would need very tight moderation and then there is still the question of how to arrange that something is actually done with the reports.

Is there an online Java language reference?

Hi,
Im looking for a reference that gives textual descriptions of the Java language. The only ones Ive found only have the syntax of the statements/classes with return values and arguments, not a description of what the class/method/variables ACTUALLY do.
thanks for your tips,
wuardo

Do you already use the Java 1.3 API documentation. This should be the first place to start when searching for classes and methods. It can be downloaded from:
http://java.sun.com/j2se/1.3/docs.html
I would also make sure you have access to the Sun Java Tutorials. It comes with example code and sample programs. It can be downloaded for free at:
http://java.sun.com/docs/books/tutorial/

Love this java language

Similar Messages

Maybe you are looking for