Java

Need help with parameterized class or method

15-Jan-09 4:24

1) you don't follow the posting guidelines and the messages formatting rules.

2) this is not Java, it is Javascript, so ask the right forum if you want to get relevant answers about this.

Also, I'm sure google knows plenty of cross-browsers working solutions

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David Crow13-Jan-09 7:36

13-Jan-09 7:36

I've got an Object array that holds various types of objects. I'm trying to code up some sort of parameterized class or method that will print the contents of those objects.

This array belongs to the framework, and is populated accordingly before a notification routine is called. For example, if the notification routine is called with a value of 100, I know the array contains Orange objects, if it is called with a value of 200, I know the array contains Apple objects, etc. In the notification routine, I need to call a "print" function that will print the contents of the object regardless of its type.

Here's how I am currently doing it:

case 100:
    Orange orange = (Orange) m_objectNames[0].getListObject();
    printContents(new Orange(), m_objectNames);
    break;
case 200:
    Apple Apple = (Apple) m_objectNames[0].getListObject();
    printContents(new Apple(), m_objectNames);
    break;

Is this clear as mud? My print function looks like:

public static <T> int printContents( T t, ObjectName objNames[] )
{
    for (int x = 0; x < objNames.length; x++)
        t = (T) objNames[x].getListObject();
}

The loop runs the correct number of times, but I can't figure out how to access the methods and properties of the T objects.

- DC

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

toxcct15-Jan-09 4:28

15-Jan-09 4:28

Hi David, coding java now ?! ^^

well, you're not really facing a Java problem, but more a polymorphism one IMO.

as long as you're handling a T (generic class), you cannot guess which methods to call...

the only thing which can be done is calling a method which is in every classes, by telling T is an interface (or an abstract base class)...

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David Crow15-Jan-09 4:51

15-Jan-09 4:51

toxcct wrote:
Hi David, coding java now ?! ^^

Yes, and have been for nearly two years now. It's been an enjoyable change.

What I have since found out is that I can use instanceof on the objects in the ObjectName[] array. It correctly reports them as being Apple, Orange, Truck, etc. My print routine now looks like:

public void printContents( ObjectName objectNames[] )
{
    if (objectNames[0] instanceof Apple)
        ...
    else if (objectNames[0] instanceof Orange)
        ...
    else if (objectNames[0] instanceof Truck)
        ...
}

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

toxcct15-Jan-09 4:55

15-Jan-09 4:55

hum, yes, I thought of that way, but since reflexion is performance consuming (IIRC), I always prefer using "regular" OOP, not tricky solution, but it's true, you can to this (and explicit cast back to the actual type before calling methods)...

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David Crow15-Jan-09 5:01

15-Jan-09 5:01

toxcct wrote:
...I always prefer using "regular" OOP, not tricky solution...

What did you have in mind?

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

toxcct15-Jan-09 5:04

15-Jan-09 5:04

class Fruit{}
class Orange extends Fruit {}
class Banana extends Fruit {}

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David Crow15-Jan-09 5:16

Re: Need help with parameterized class or method [modified]

15-Jan-09 5:16

In reality, that is what I have in place:

class InfoBase
{
}
 
class MessageBase extends InfoBase
{
    String strDate;
    String strTime;
}
 
class RecipientBase extends InfoBase
{
    String strName;
}

"Love people and use things, not love things and use people." - Unknown

"The brick walls are there for a reason...to stop the people who don't want it badly enough." - Randy Pausch

Naruki9-Feb-09 15:18

Naruki

9-Feb-09 15:18

Somewhere at home I have a wicked cool printing function that I tweaked from the original code, taken from an online article. I even got the author to suggest some improvements. Unfortunately, I'm at work and the whole thing is based on reflection.

What you seem to want is to override the toString() method.

By default, your objects will use Object.toString(), which merely prints out a hash code or some such. Not very useful for complex requirements.

Override it in your ~~Fruit~~ InfoBase class to print out whatever it is you want. Then, override it again in the subclasses only if you have special changes that the super class cannot see.

[Edited: just realized Fruit was not your class.]

If you want a one-size fits all solution, however, you'll definitely need reflection. If I remember to look tonight, I'll see if I can find that class.

Don't let my name fool you. That's my job.

modified on Monday, February 9, 2009 9:30 PM

need source code for our project

Lakshmi4108712-Jan-09 4:33

Lakshmi41087

12-Jan-09 4:33

Hi all.. our project is an IEEE paper.Title of the project is "Application of Software Agent to e-Commerce consumer buying support".Where can i get the source code for this project?at least i need some code snippets for this project.Kindly guide us.

Hello World Java Program

prithaa11-Jan-09 6:10

prithaa

11-Jan-09 6:10

Hello,

I have downloaded Sun Java SE version and NetBeans but dont know where to run the Hello World program.It seems that I should not use NetBeans before I know the basics of Java programming.
I am a VC++ programmer and aware of object oriented language.

Need Help

Prithaa

Re: Hello World Java Program

tamour12-Jan-09 0:49

Re: Hello World Java Program

12-Jan-09 0:49

hi,
simply click on the 'file' menu in netbeans and make a new project. Select 'Java' from 'catagory' pane and 'Java Application' from 'project' pane. click next and then finish. File 'main.java' will open itself with the following code in it.

/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */

package javaapplication2;

/**
 *
 * @author Tamour
 */
public class Main {

    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        // TODO code application logic here
    }

}

add the following statement in static main after "// TODO code application logic here".

System.out.println("Hello World!");

NetBeans is a very good IDE. infact not that much like Visual studio but still good enough. I can provide you with some tutorials if you want.

prithaa15-Jan-09 18:06

prithaa

15-Jan-09 18:06

Hello,
Thanks for your help,

Yes I do want the tutorials.

Pritha

The best starting point tutorial...

Naruki9-Feb-09 15:01

Naruki

9-Feb-09 15:01

is Sun's very own.

If you are using NetBeans (or Eclipse or another IDE), then you won't need to worry too much about the installation stuff.

If you want to do things the hard way (as Sun's tutorials assume), then you need to make sure you follow the installation guide carefully. Mainly so the Java binaries are in the system path.

When you do it this way, you will have to understand how the package hierarchy works and where you need to be relative to that when you launch your programs. It's a real PITA, but the experience is very helpful. Good luck.

Am i converting the code right ?

tamour9-Jan-09 11:49

Re: Am i converting the code right ?

9-Jan-09 11:49

private void button_Click(object sender, EventArgs e)
{
  SerialPort sp = new SerialPort(SerialPort.GetPortNames()[0], 9600, Parity.None, 8, StopBits.One);
  String[] str = SerialPort.GetPortNames();
  sp.Open();
  sp.DtrEnable = true;
  sp.RtsEnable = true;
  sp.WriteLine("Hello World!");
  sp.Close();
}

Java

Enumeration pList = CommPortIdentifier.getPortIdentifiers();
CommPortIdentifier cpi = (CommPortIdentifier) pList.nextElement();

if (cpi.getPortType() == CommPortIdentifier.PORT_SERIAL && cpi.getName().compareTo("COM1") == 0) {

  try {
     CommPort port = cpi.open("DarwinSys Printing", 30 * 1000);
      try {
        OutputStream os = port.getOutputStream();
        String str = "Hello World!";
        byte[] b = str.getBytes();
        os.write(b);
        os.flush();
        os.close();
      } catch (IOException ex) {
      }

// i also tried the code below

//   try {
//   serial.setSerialPortParams(9600, SerialPort.DATABITS_8,
//   SerialPort.STOPBITS_1, SerialPort.PARITY_NONE);
//   } catch (UnsupportedCommOperationException ex) {
//   }
//    serial.setDTR(true);
//    serial.setRTS(true);
//    serial.notifyAll();
//
//   try {
//     OutputStream os = (OutputStream) serial.getOutputStream();
//     String str = "Hello World!";
//     byte[] b = str.getBytes();
//     os.write(b);
//     os.flush();
//     os.close();
//   } catch (IOException ex) {
//   }
     } catch (PortInUseException ex) {
     }

I have a device on the serial port which has a led on it. The LED blinks on the C#'s code. I think the code i have written in java is approximately doing the samething but the LED does not blink.

thanks in advance.

itsmani27-Jan-09 22:13

itsmani

27-Jan-09 22:13

Hi team,
plz explain this program how to run, i want full source code..

thanks
MANI.G

Cannot access database

tamour9-Jan-09 3:19

Developing a discussion forum using java?

9-Jan-09 3:19

I got a kind of weird problem. I have created a Java Desktop Application project in NetBeans. I have created a new java class say A. Class A does not has MAIN in it. It contains just METHODS like insert, delete, update, openConnection, closeConection and others like that. To test the class A, I created the MAIN in it and tried to connect to the database, the database connects successfully and all the methods work aswell.

I created a button on the java application and the method which is called when the button is called is named as button1Pressed. Here is the simple code in the button event.

@Action
    public void button1Pressed() {
        A a = new A();
        a.openConnection();
    }

Here is the method in class A

// this is the method in the class A

public void openConnection() {
    String connectionString = "jdbc:mysql://172.16.11.12:3306/Projector_Manager";
    try {
       Class.forName("com.mysql.jdbc.Driver");
       conn = DriverManager.getConnection(connectionString,"root","1");  // here comes the error
       insertStatement = conn.prepareStatement("insert into Current_Status values (?,?,?,?,?)");
         } catch (SQLException ex) {
         System.out.println(ex.getMessage());
         } catch (ClassNotFoundException ex) {
         System.out.println(ex.getMessage());
         }
    }

The error on the statement is

Communications link failure<br />
<br />
Last packet sent to the server was 1 ms ago.

the error comes after 4-5 minutes and until then the application hangs.

but when I declare MAIN in the class A like

public static void main(String[] args)
{
    A a = new A();
    a.openConnection();
}

and execute the code it connects to the database fine.

I dont know why it connects to the database the single file is executed and not when i run the GUI and press the button and it goes to the same code and does not connect.

I have also pasted the whole code in the button1Pressed but still it does not connects to the database

avvisaan8-Jan-09 4:59

avvisaan

8-Jan-09 4:59

Can any some say whether its possible to develop a discussion forum using core java? if so can somebody share info on how to start on with that...

Port address Translation

bobbo886-Jan-09 5:16

bobbo88

6-Jan-09 5:16

hi i need to know how to impliment port adress translation for a simulator program, can anyone help

many thanks

Help Please (java only please)

bobbo886-Jan-09 3:40

bobbo88

6-Jan-09 3:40

Hi
i know this is possile but i dont know how. i need to set up multiple IP adresses on a single machine using java and forward each IP to a specified port. can some one please point me in the right direction to creating multiple IPs on a single machine.

note this is for a simulator program and requires the possibility to create a few hundred IP's.

many thanks
rich

Re: Help Please (java only please)

tamour9-Jan-09 11:56