Re: problem with inheritance - Java Discussion Boards

Re: problem with inheritance

Richard MacCutchan18-Sep-13 2:51

Richard MacCutchan

18-Sep-13 2:51

Why is foo declared as static?

Veni, vidi, abiit domum

Re: problem with inheritance

Asaf Shay19-Sep-13 9:17

Asaf Shay

19-Sep-13 9:17

i don't know .i take this question from exam

Re: problem with inheritance

jschell19-Sep-13 11:26

jschell

19-Sep-13 11:26

Asaf Shay wrote:

i don't know .i take this question from
exam

However that is the clue as to the answer to the question.

Re: problem with inheritance

linaast18-Sep-13 20:38

linaast

18-Sep-13 20:38

You do not need to create the instance into base class. If you have base class, leave it, every class, which extends the base class as father class makes instances to it automatically. All you need is to put "super" modifier, if u need to call any function from your base class.

I suggest you to do like this in this case:

Java

public class OverrideTest{
 public static void main(String[] args){
  Derived dObj = new Derived();
  dObj.foo();
 } 
}

public class Derived extends Base{
 public void foo(){
  System.out.println("In Derived.foo()");
  super.foo();
 }
}

public class Base{
 public void foo(){
  System.out.println("In Base.foo()");
 }
}

Now your output will be:
"In Derived.foo()"
"In Base.foo()"

You do not need to use this:

Java

Base bObj = new Derived();

If You want to call the foo() method of Base class directly from yor Main class, remove the foo() method from your Derived class. In this case, the foo() method will be called from Base class automatically.

modified 19-Sep-13 9:53am.

Re: problem with inheritance

Asaf Shay19-Sep-13 9:24

Asaf Shay

19-Sep-13 9:24

this question is from exam .so i don't want to make the code better or different . i only want to know what i ask .

Re: problem with inheritance

Mr_z22-Sep-13 10:36

Mr_z

22-Sep-13 10:36

שלום אסף --

אלה התיקונים שצריך להכניס כדי שהתוצאה תראה כפי שרצית

1] Derived bObj = new Derived() ;
2] class Derived extends Base
public static void foo(Derived bObj)

אני חושב שהתוצאה הלא נכונה נגרמת בגלל "דריסה" לא נכונה של המחלקה היורשת

Re: problem with inheritance

Usama Moud27-Sep-13 9:36

Usama Moud

27-Sep-13 9:36

foo() in Base class is declared as Static. Therefore it is not belonged to specific object but common for all objects.

bObj is an object of Base class, therefore it will call foo() in Base class, because foo() is Static.

Re: problem with inheritance

angrybobcat29-Sep-13 9:57

angrybobcat

29-Sep-13 9:57

To explain that, take a look at what is executed and why.

First of all, you create a new Derived-Instance as an instance of Base.

Take a look at how you call the static method foo():
You dont access it in a static way (to use exact the phrase the compiler will warn you with) - which would be Base.foo() or Derived.foo() - but you call it on an instance.

As mentioned, bObj is an instance of Base (because you declared it as that) and thus the static Method Base.foo() is called, which prints the "In Base.foo()"-Part of your output.

If you declared it as an instance of Derived, the static method Derived.foo() would have been called there.

To explain the part "In Derived.bar()" take a look at what is called next:
In Base.bar() you call bObj.bar();

bObj was instantiated with new Derived(), so the method bar() on that object is overriden with the implementation in Derived, which prints then "In Derived.bar()".

I hope that explains inheritance a bit better.

ab

Re: problem with inheritance

Vivek Vermani13-Jan-14 12:04

Vivek Vermani

13-Jan-14 12:04

Java doesn't allow overriding static methods and runtime polymorphism on static methods.

Why Java Doesn't allow run time Polymorphism by overriding static methods.

Please Help with a Java code

Adewagold16-Sep-13 22:01

Adewagold

16-Sep-13 22:01

i'm still new to java, but i want to create a java application for mobile phones, which will perform the following functions for sending sms online
get Username and password of the user
Message Sender ID,
Recipient numbers or select from contact list
the message
then the send button which will make use of sms API

Re: Please Help with a Java code

Richard MacCutchan17-Sep-13 0:33

Richard MacCutchan

17-Sep-13 0:33

Please use Google to do some research first. It is not possible to provide all this information in a technical forum.

Veni, vidi, abiit domum

Re: Please Help with a Java code

Member 1028017517-Sep-13 7:04

Member 10280175

17-Sep-13 7:04

import java.awt.*;
import java.awt.event.*;
import java.net.*;
import java.io.*;

public class server extends Frame implements ActionListener, Runnable
{
Image Icon = Toolkit.getDefaultToolkit().getImage("hi.gif");
ServerSocket ss;
Socket s;
BufferedReader br;
BufferedWriter bw;
TextField text;
Button sendBut, exitBut;
List list;

public server(String m) // class constructor
{
super(m);
setSize(300, 130);
setLocation(0,0);
setIconImage(Icon);
setResizable(false);
setBackground(new Color(192, 192, 192));
this.setLayout(new GridLayout(2, 1));

Panel panels[] = new Panel[2];
panels[0] = new Panel();
panels[1] = new Panel();
panels[0].setLayout(new BorderLayout());
panels[1].setLayout(new FlowLayout(FlowLayout.LEFT));

sendBut = new Button("Send");
exitBut = new Button("Exit");

sendBut.addActionListener(this);
exitBut.addActionListener(this);

list = new List();
list.addItem("Server up & Listening on port plz wait...");

text = new TextField(25);

panels[0].add(list);
panels[1].add(text);
panels[1].add(sendBut);
panels[1].add(exitBut);

add(panels[0]);
add(panels[1]);

setVisible(true);

try
{
ss = new ServerSocket(1053);//some port number, better be above 1000
s = ss.accept();
br = new BufferedReader(new InputStreamReader(s.getInputStream()));
bw = new BufferedWriter(new OutputStreamWriter(s.getOutputStream()));
bw.write("Hi! ASL plz??");
bw.newLine();
bw.flush();
Thread th;
th = new Thread(this);
th.start();

}catch(Exception e){}

}

public void run()
{
while (true)
{
try
{
list.addItem(br.readLine());
}catch (Exception e){}
}
}

public static void main(String arg[])
{
// create an object instance
// by sending the title as a parameter
new server("Server Applicaton");
}

public void actionPerformed(ActionEvent ae)
{
if (ae.getSource().equals(exitBut))
System.exit(0);
else
{
try
{
bw.write(text.getText());
bw.newLine();bw.flush();
text.setText("");
}catch(Exception x){}
}

}

}

JSpinner Value into Database?

chdboy15-Sep-13 19:46

chdboy

15-Sep-13 19:46

How would I get the JSpinner value into database?,
the value is in alphanumeric

Like
1month
2month

Java

String[] monthStrings = {"1Month","3Month","6Month","1Year"}; 
        SpinnerListModel monthModel = new SpinnerListModel(monthStrings);
        JSpinner spinner = new JSpinner(monthModel);

Re: JSpinner Value into Database?

Richard MacCutchan15-Sep-13 21:20

Richard MacCutchan

15-Sep-13 21:20

chdboy wrote:
How would I get the JSpinner value into database?

The same way you would put any value into the database; what exactly is the difficulty? Given also that it is just a short list, maybe storing the index value rather than the string would be the best idea.

Veni, vidi, abiit domum

Re: JSpinner Value into Database?

chdboy15-Sep-13 21:31

chdboy

15-Sep-13 21:31

Here is the code ,how I'm saving the JSpinner value

Java

statement.setString(27,JSpinner.getValue());

Under setString red line and the error is

The method setString(int, String) in the type PreparedStatement is not applicable for the arguments (int, Object)

and Under

Java

JSpinner.getValue()

red line and error says

Cannot make a static reference to the non-static method getValue() from the type JSpinner

Re: JSpinner Value into Database?

Richard MacCutchan15-Sep-13 21:43

Richard MacCutchan

15-Sep-13 21:43

You cannot use JSpinner.getValue(), you need to call getValue() on an instance of the JSpinner class.

Veni, vidi, abiit domum

Re: JSpinner Value into Database?

chdboy17-Sep-13 3:46

chdboy

17-Sep-13 3:46

I tried

statement.setString(27,(String)spinner.getValue());

and I get

Exception in thread "AWT-EventQueue-0" java.lang.ClassCastException: java.lang.Integer cannot be cast to java.lang.String

EDIT:
It worked with

statement.setString(27,(String)spinner.getValue().toString());

modified 17-Sep-13 9:54am.

Re: JSpinner Value into Database?

Richard MacCutchan17-Sep-13 3:55

Richard MacCutchan

17-Sep-13 3:55

You should go back to your Java documentation or tutorials and learn why and when it is possible to use casts. Simply stated, you cannot use a cast to convert one object type to another. You also need to decide in advance what object type you want to store in the database, and write the code to handle that specific situation.

Veni, vidi, abiit domum

join

Member 1027264513-Sep-13 7:32

Member 10272645

13-Sep-13 7:32

can i join your grope ?

longkimnoy

Re: join

jschell13-Sep-13 11:39

jschell

13-Sep-13 11:39

grope=feel about or search blindly or uncertainly with the hands.
group=a number of people or things that are located close together or are considered or classed together.

You have already done the second.

Re: join

Richard MacCutchan13-Sep-13 22:46

Richard MacCutchan

13-Sep-13 22:46

Read the rules[^] first.

Veni, vidi, abiit domum

SEVERE: Error listenerStart

r_mohd13-Sep-13 5:59

r_mohd

13-Sep-13 5:59

Hi all,

I am new to java; earlier i was working in .net (c#). My company assigned me an existing web project which is developed in java (jsp). i have installed jdj7 and Apache Tomcat 7 as service on my machine. Whenever i placed my project in webapps folder it generate an error in logs (Catalina)

CSS

Sep 12, 2013 3:11:45 AM org.apache.catalina.startup.HostConfig deployDirectory
INFO: Deploying web application directory C:\Tomcat 7\webapps\myproject
Sep 12, 2013 3:11:57 AM org.apache.catalina.core.StandardContext startInternal
SEVERE: Error listenerStart
Sep 12, 2013 3:11:57 AM org.apache.catalina.core.StandardContext startInternal
SEVERE: Context [/myproject] startup failed due to previous errors