Difference between inheritance and abstract class

difference between inheritance and abstract class

See this thread:
http://forum.java.sun.com/thread.jspa?forumID=24&threadID=663657
And before Post New Topic, just search in this forums. All most will get answers.

Similar Messages

Difference between Datahiding and Abstraction - OOPS

Hi,
I got stuck in finding the exact difference in these two.
1. Datahiding is achieved through the access specifiers or by using it inside the function or also by using it inside the class.
2. Abstraction means showing the necessary details and hiding the necessary details.
If the above definition for the abstraction is correct then datahiding and abstraction become similar, correct.?
Could u guys help me to clarify with example.
Thanks in advance.
NANDAKUMAR.T

Abstraction is like saying, "I don't care what it is, as long as it can be used the way I want, that's good enough for me."
A good example is the interface that you need to be able to drive a car, such as a manual transmission vs an automatic transmission. As long as the car has the expected interface (a steering wheel, gas / brake pedals, etc.) you should be able to drive
it. You can interface with a car in an abstract way. You shouldn't have to care about details of spark plugs just to drive the car. An "automatic transmission car" is an abstract class of car.
A concrete class of car would be a very specific make and model, that would come out of a factory according to some specifications.
You may ask a car rental agency for an "automatic transmission car", and then what you'll get is still some specific make and model of car, but you just don't care about what it is.
Data hiding just means that you don't get a description of the the details of all your data. If something's marked private, it means that the details of the definition need not go any further. In terms of a car, again, these are aspects of the
vehicle that don't go into the user manual. The parts are still there, but there's no obligation to provide a description of what the parts are. For example, there are many components in a car that are complex and sophisticated, but have simple
descriptions, are are replaced in their entirety then they fail, such as an "alternator". There's likely no public description of the contents of the alternator. "No user serviceable parts inside" is part of "data hiding".
You can achieve data hiding through abstraction. You can also achieve data hiding with access modifiers (public, private, protected, internal).
The differences in the terms you mentioned are should be taken quite literally. abstract, refers to the idea of a thing, without a concrete instance of the thing, and we use it to be able to substitute a one concrete thing for another, or
to design in anticipation of something that doesn't exist yet. And hiding data just means concealing data from view -- usually with hopes that people won't monkey around with things that are concealed.

What is the difference between StringBuffer and StringBuilder objects

hi ,
Please tell me what is the difference between stringBuilder and stringBuffer classes ..why stringbuffer classes is used more with multiple threads but not stringBuilder which is faster than stringBuffer objects
Thanks in advance

Odd. You answer your own question by paraphrasing the first paragraph of
StringBuilder's javadoc:
This class provides an API compatible with StringBuffer, but with no guarantee
of synchronization. This class is designed for use as a drop-in replacement for
StringBuffer in places where the string buffer was being used by a single thread
(as is generally the case). Where possible, it is recommended that this class
be used in preference to StringBuffer as it will be faster under most
implementations.
Do you really have a question?

What's the difference between setFollowRedirect() and setinstanceFollowRedi

What's the difference between setFollowRedirect() and setInstanceFollowRedirect() ?????

Hi there,
setFollowRedirects and setInstanceFollowRedirects both set flags that indicate whether or not the HtppURLConnection should follow a redirect if it receives one from the server that it is connecting to. The difference is that setFollowRedirects() is a static method that changes the behaviour for all instances of the HttpURLConnection class (or more likely the implementation class, HttpURLConnection is abstract) and setInstanceFollowRedirects() just changes it for the instance on which you call it.
BTW: The field set by setFollowRedirects is private (followRedirects) while the flag set by setInstanceFollowDirects is protected and is listed in the API docs (instanceFollowRedirects)
Hope this helps
Amanda

Differences between BADIS and User-exits

Hi everybody,
I am new to ABAP and wonder what are the differences between BADIS and User-Exits. I read paper but did not find a SAP documentation yet.
Does anybody know where to find a sap document which explains both technologies?
Greetings, AD

Hi,
User-Exit is a specific place in a transaction-process where SAP offers
third parties to include there own business functionality. Actually
User-Exit is the namespace used for Exits programmed by SAP specifically
for SD. For the other modules it's called Customer-Exit.=20
>Business Add-Ins (BADI) =20
The use of object orientated code within SAP has lead to new method of
enhancing standard SAP code called Business Add-Ins or BADI's for short.
Although the implementation concept is based on classes, methods and
inheritance you do not really have to understand this fully to implement
a BADI.
For better understanding visit.
http://sap.ittoolbox.com/groups/technical-functional/sap-r3-dev/779183#
Hope it was useful.
Thansk,
Sandeep.

Difference between implements and extends

Hi all,
what is the difference between implements and extends. i am sorry to ask this silly question, but i am new to JAVA.
Thanks
Balaji

when you extend a class, your class that you are coding inherits every method and field from the extending class. For example:
public class CustomFrame extends JFrame {
//Your class's methods will be in here, but so will all of JFrame's methods.
}You can override (most) methods from extended classes if you want them to do different things than they normally do. The most commonly overriden methods when using swing are stuff like paint(Graphics g). It needs to be overriden to repaint all of the components.
When you imlpement something, you have to specify an interface. Interfaces have methods in them with no code. If you implement an interface, all methods in in must be defined. If not, the code will not compile. Some interfaces like ActionListener extend other classes to perform stuff. The actionPerformed(ActionEvent e) method will perform an action when a button is pressed, etc.

Difference between Implement and Extend

what is the difference between implements and extends and why do we use them
thanks,

classes extend one other class and implement as many
interfaces as they wish.
interfaces extend as many interfaces as they wish.But for all that, they both just mean "inherits."
There wouldn't even have to be two different words, since you never have a choice between X extends Y and X implements Y. For a given X and Y, only one of the two will be legal.

Differences between awt and swing

Ive written the following code, however Ive implemented the gui in awt rather then swing. Ive been told it hs too be in swing. What is the difference between swing and awt what will I need to change in my program so that its done using swing rather then the awt? Heres the code:
// pp.java
// Grant Brown
// 22/02/02
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
// =========================================================
// Class: pp
// This class drives the customer manager. It contains the
// main method which gets called as soon as this application
// begins to run.
// =========================================================
class pp extends Frame implements ActionListener
// Container of customer objects
private Vector customers = new Vector (100);
// List of names component. (Must specify java.awt in
// front of List to distinguish the List class in the
// java.awt package from the List class in the java.util
// package.)
private java.awt.List names = new java.awt.List ();
// Delete and update button components.
private Button delete;
private Button update;
// Default constructor.
public pp ()
// Assign "Paper Round Manager" to title bar of frame window.
super ("Paper Round Manager");
// Add a listener that responds to window closing
// events. When this event occurs (by clicking on the
// close box in the title bar), save customers and exit.
addWindowListener (new WindowAdapter ()
public void windowClosing
(WindowEvent e)
saveCustomers ();
System.exit (0);
// Place an empty label in the north part of the frame
// window. This is done to correct an AWT positioning
// problem.
Label l = new Label ();
add ("North", l);
// Place the names component in the center part of the
// frame window.
add ("Center", names);
// Create a panel object to hold four buttons.
Panel p = new Panel ();
Button b;
// Add an Insert button to the Panel object and register
// the current pp object as a listener for button events.
p.add (b = new Button ("Insert"));
b.addActionListener (this);
// Add a Delete button to the Panel object and register
// the current pp object as a listener for button events.
p.add (delete = new Button ("Delete"));
delete.addActionListener (this);
// The Delete button should be disabled until there is at
// least one customer to delete.
delete.setEnabled (false);
// Add an Update button to the Panel object and register
// the current pp object as a listener for button events.
p.add (update = new Button ("Update"));
update.addActionListener (this);
// The Update button should be disabled until there is at
// least one customer to update.
update.setEnabled (false);
// Add a Finish button to the Panel object and register
// the current customer object as a listener for button events.
p.add (b = new Button ("Finish"));
b.addActionListener (this);
// Add the panel object to the frame window container.
add ("South", p);
// Set the background of the frame window container to
// lightGray
setBackground (Color.lightGray);
// Set the size of the frame window container to 400
// pixels horizontally by 200 pixels vertically.
setSize (400, 200);
// Allow the user to resize the frame window.
setResizable (true);
// Load all contacts.
loadCustomers ();
// Make sure that the frame window is visible.
setVisible (true);
public void actionPerformed (ActionEvent e)
if (e.getActionCommand ().equals ("Delete"))
delete ();
else
if (e.getActionCommand ().equals ("Finish"))
saveCustomers ();
System.exit (0);
else
if (e.getActionCommand ().equals ("Insert"))
insert ();
else
update ();
public Insets getInsets ()
// Return an Insets object that describes the number of
// pixels to reserve as a border around the edges of the
// frame window.
return new Insets (10, 10, 10, 10);
public static void main (String [] args)
// Create a new pp object and let it do its thing.
new pp ();
private void delete ()
// Obtain index of selected contact item from the names
// component.
int index = names.getSelectedIndex ();
// If no item was selected, index is -1. We cannot update
// a contact if no contact item in the names component was
// selected - because we would have nothing to work with.
if (index != -1)
// Remove the contact item from the names component.
names.remove (index);
// Remove the Customer object from the contacts Vector
// object.
customers.remove (index);
// If there are no more customers ...
if (customers.size () == 0)
delete.setEnabled (false);
update.setEnabled (false);
else
// Make sure that the first contact item in the names
// list is highlighted.
names.select (0);
private void insert ()
// Create an Insert data entry form to enter information
// for a new customer.
DataEntryForm def = new DataEntryForm (this, "Insert");
// If the bOk Boolean flag is set, this indicates the user
// exited the form by pressing the Ok button.
if (def.bOk)
// Create a Contact object and assign information from
// the form to its fields.
Customer temp = new Customer ();
temp.name = new String (def.name.getText ());
temp.publication = new String (def.publication.getText ());
temp.round = new String (def.round.getText ());
temp.address = new String (def.address.getText ());
temp.phone = new String (def.phone.getText ());
// Add a new customer item to the names component.
names.add (temp.name + ", " + temp.publication);
// Add the Customer object to the contacts Vector
// object.
customers.add (temp);
// Make sure that the Delete and Update buttons are
// enabled.
delete.setEnabled (true);
update.setEnabled (true);
// Destroy the dialouge box.
def.dispose ();
// Make sure that the first customer item in the names list
// is highlighted.
names.select (0);
// ===========================================================
// Load all contacts from contacts.dat into the contacts
// Vector object. Also, make sure that the last name/first
// name from each contact is combined into a String object and
// inserted into the names component - as a contact item.
// ===========================================================
private void loadCustomers ()
FileInputStream fis = null;
try
fis = new FileInputStream ("Customers.dat");
DataInputStream dis = new DataInputStream (fis);
int nCustomers = dis.readInt ();
for (int i = 0; i < nCustomers; i++)
Customer temp = new Customer ();
temp.name = dis.readUTF ();
temp.publication = dis.readUTF ();
temp.round = dis.readUTF ();
temp.address = dis.readUTF ();
temp.phone = dis.readUTF ();
names.add (temp.name + ", " + temp.publication);
customers.add (temp);
if (nCustomers > 0)
delete.setEnabled (true);
update.setEnabled (true);
catch (IOException e)
finally
if (fis != null)
try
fis.close ();
catch (IOException e) {}
// Make sure that the first contact item in the names list
// is highlighted.
names.select (0);
// ========================================================
// Save all Customer objects from the customer Vector object
// to customer.dat. The number of customerss are saved as an
// int to make it easy for loadCustomers () to do its job.
// ========================================================
private void saveCustomers ()
FileOutputStream fos = null;
try
fos = new FileOutputStream ("customers.dat");
DataOutputStream dos = new DataOutputStream (fos);
dos.writeInt (customers.size ());
for (int i = 0; i < customers.size (); i++)
Customer temp = (Customer) customers.elementAt (i);
dos.writeUTF (temp.name);
dos.writeUTF (temp.publication);
dos.writeUTF (temp.round);
dos.writeUTF (temp.address);
dos.writeUTF (temp.phone);
catch (IOException e)
MsgBox mb = new MsgBox (this, "PP Error",
e.toString ());
mb.dispose ();
finally
if (fos != null)
try
fos.close ();
catch (IOException e) {}
private void update ()
// Obtain index of selected customer item from the names
// component.
int index = names.getSelectedIndex ();
// If no item was selected, index is -1. We cannot update
// a customer if no customer item in the names component was
// selected - because we would have nothing to work with.
if (index != -1)
// Obtain a reference to the customer object (from the
// customers Vector object) that is associated with the
// index.
Customer temp = (Customer) customers.elementAt (index);
// Create and display an update entry form.
DataEntryForm def = new DataEntryForm (this, "Update",
temp.name,
temp.publication,
temp.round,
temp.address,
temp.phone);
// If the user pressed Ok...
if (def.bOk)
// Update the customer information in the customers
// Vector object.
temp.name = new String (def.name.getText ());
temp.publication = new String (def.publication.getText ());
temp.round = new String (def.round.getText ());
temp.address = new String (def.address.getText ());
temp.phone = new String (def.phone.getText ());
// Make sure the screen reflects the update.
names.replaceItem (temp.name + ", " + temp.publication,
index);
// Destroy the dialouge box.
def.dispose ();
// Make sure that the first customer item in the names
// list is highlighted.
names.select (0);

Ive doen pretty much what you said burt now my program isnt working at all. The window comes up but instead of doing something when you click the button it just throws shit loads of exceptions. Heres my abridged code
// pp.java
// Grant Brown
// 22/02/02
import java.awt.*;
import java.awt.event.*;
import java.io.*;
import java.util.*;
import javax.swing.*;
// =========================================================
// Class:PP
// This class drives the Paper Round manager. It contains the
// main method which gets called as soon as this application
// begins to run.
// =========================================================
class pp extends JFrame implements ActionListener
// Container of customer objects (one object per customer)
private Vector customers = new Vector (100);
// List of names component. (Must specify java.awt in
// front of List to distinguish the List class in the
// java.awt package from the List class in the java.util
// package.)
private java.awt.List names = new java.awt.List ();
// Delete and update button components.
private JButton delete;
private JButton update;
// Default constructor.
public pp ()
// Assign Contact Manager to title bar of frame window.
super ("Paper Round Manager");
// Add a listener that responds to window closing
// events. When this event occurs (by clicking on the
// close box in the title bar), save contacts and exit.
addWindowListener (new WindowAdapter ()
public void windowClosing
(WindowEvent e)
saveCustomers ();
System.exit (0);
// Place an empty label in the north part of the frame
// window. This is done to correct an AWT positioning
// problem. (One thing that you'll come to realize as
// you work with the AWT is that there are lots of bugs.)
JLabel l = new JLabel ();
getContentPane().add ("North", l);
// Place the names component in the center part of the
// frame window.
getContentPane().add ("Center", names);
// Create a panel object to hold four buttons.
JPanel p = new JPanel ();
JButton b;
// Add an Insert button to the Panel object and register
// the current cm object as a listener for button events.
p.add (b = new JButton ("Insert"));
b.addActionListener (this);
// Add a Delete button to the Panel object and register
// the current cm object as a listener for button events.
p.add (delete = new JButton ("Delete"));
delete.addActionListener (this);
// The Delete button should be disabled until there is at
// least one contact to delete.
delete.setEnabled (false);
// Add an Update button to the Panel object and register
// the current cm object as a listener for button events.
p.add (update = new JButton ("Update"));
update.addActionListener (this);
// The Update button should be disabled until there is at
// least one contact to update.
update.setEnabled (false);
// Add a Finish button to the Panel object and register
// the current cm object as a listener for button events.
p.add (b = new JButton ("Finish"));
b.addActionListener (this);
// Add the panel object to the frame window container.
getContentPane().add ("South", p);
// Set the background of the frame window container to
// lightGray (to give a pleasing effect).
setBackground (Color.lightGray);
// Set the size of the frame window container to 400
// pixels horizontally by 200 pixels vertically.
setBounds (50, 100, 400, 200);
// Do not allow the user to resize the frame window.
loadCustomers ();
// Load all contacts.
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
// Make sure that the frame window is visible.
setVisible (true);
public void actionPerformed (ActionEvent e)
if (e.getActionCommand ().equals ("Delete"))
delete ();
else
if (e.getActionCommand ().equals ("Finish"))
saveCustomers ();
System.exit (0);
else
if (e.getActionCommand ().equals ("Insert"))
insert ();
else
update ();
public Insets getInsets ()
// Return an Insets object that describes the number of
// pixels to reserve as a border around the edges of the
// frame window.
return new Insets (10, 10, 10, 10);
public static void main (String [] args)
// Create a new cm object and let it do its thing.
new pp ();
private void delete ()
// Obtain index of selected customer item from the names
// component.
int index = names.getSelectedIndex ();
// If no item was selected, index is -1. We cannot update
// a contact if no contact item in the names component was
// selected - because we would have nothing to work with.
if (index != -1)
// Remove the customer item from the names component.
names.remove (index);
// Remove the Customer object from the contacts Vector
// object.
customers.remove (index);
// If there are no more customers ...
if (customers.size () == 0)
delete.setEnabled (false);
update.setEnabled (false);
else
// Make sure that the first contact item in the names
// list is highlighted.
names.select (0);
private void insert ()
// Create an Insert data entry form to enter information
// for a new contact.
DataEntryForm def = new DataEntryForm (this, "Insert");
// If the bOk Boolean flag is set, this indicates the user
// exited the form by pressing the Ok button.
if (def.bOk)
// Create a Customer object and assign information from
// the form to its fields.
Customer temp = new Customer ();
temp.name = new String (def.name.getText ());
temp.publication = new String (def.publication.getText ());
temp.address = new String (def.address.getText ());
temp.round = new String (def.round.getText ());
temp.phone = new String
(def.phone.getText ());
// Add a new customer item to the names component.
names.add (temp.publication + ", " + temp.address);
// Add the Customer object to the contacts Vector
// object.
customers.add (temp);
// Make sure that the Delete and Update buttons are
// enabled.
delete.setEnabled (true);
update.setEnabled (true);
// Destroy the dialog box.
def.dispose ();
// Make sure that the first customer item in the names list
// is highlighted.
names.select (0);
// ===========================================================
// Load all customers from customers.dat into the customers
// Vector object. Also, make sure that the last name/first
// name from each contact is combined into a String object and
// inserted into the names component - as a contact item.
// ===========================================================
private void loadCustomers ()
FileInputStream fis = null;
try
fis = new FileInputStream ("customers.dat");
DataInputStream dis = new DataInputStream (fis);
int nCustomers = dis.readInt ();
for (int i = 0; i < nCustomers; i++)
Customer temp = new Customer ();
temp.name = dis.readUTF ();
temp.publication = dis.readUTF ();
temp.address = dis.readUTF ();
temp.round = dis.readUTF ();
temp.phone = dis.readUTF ();
names.add (temp.publication + ", " + temp.address);
customers.add (temp);
if (nCustomers > 0)
delete.setEnabled (true);
update.setEnabled (true);
catch (IOException e)
finally
if (fis != null)
try
fis.close ();
catch (IOException e) {}
// Make sure that the first customer item in the names list
// is highlighted.
names.select (0);
// ========================================================
// Save all customer objects from the contacts Vector object
// to customers.dat. The number of contacts are saved as an
// int to make it easy for loadCustomers () to do its job.
// ========================================================
private void saveCustomers ()
FileOutputStream fos = null;
try
fos = new FileOutputStream ("customers.dat");
DataOutputStream dos = new DataOutputStream (fos);
dos.writeInt (customers.size ());
for (int i = 0; i < customers.size (); i++)
Customer temp = (Customer) customers.elementAt (i);
dos.writeUTF (temp.name);
dos.writeUTF (temp.publication);
dos.writeUTF (temp.address);
dos.writeUTF (temp.round);
dos.writeUTF (temp.phone);
catch (IOException e)
MsgBox mb = new MsgBox (this, "PP Error",
e.toString ());
mb.dispose ();
finally
if (fos != null)
try
fos.close ();
catch (IOException e) {}
private void update ()
// Obtain index of selected customer item from the names
// component.
int index = names.getSelectedIndex ();
// If no item was selected, index is -1. We cannot update
// a customer if no customer item in the names component was
// selected - because we would have nothing to work with.
if (index != -1)
// Obtain a reference to the Customer object (from the
// customer Vector object) that is associated with the
// index.
Customer temp = (Customer) customers.elementAt (index);
// Create and display an update entry form.
DataEntryForm def = new DataEntryForm (this, "Update",
temp.name,
temp.publication,
temp.address,
temp.round,
temp.phone);
// If the user pressed Ok...
if (def.bOk)
// Update the customer information in the customers
// Vector object.
temp.name = new String (def.name.getText ());
temp.publication = new String (def.publication.getText ());
temp.address = new String (def.address.getText ());
temp.round = new String (def.round.getText ());
temp.phone = new String (def.phone.getText ());
// Make sure the screen reflects the update.
names.replaceItem (temp.publication + ", " + temp.address,
index);
// Destroy the dialog box.
def.dispose ();
// Make sure that the first customer item in the names
// list is highlighted.
names.select (0);
// ========================================================
// Class: Customer
// This class describes the contents of a business customer.
// ========================================================
class Customer
public String name;
public String publication;
public String address;
public String round;
public String phone;
// ==========================================================
// Class: DataEntryForm
// This class provides a data entry form for entering customer
// information.
// ==========================================================
class DataEntryForm extends JDialog implements ActionListener
// bOk is a boolean flag. When true, it indicates that
// the Ok button was pressed to terminate the dialog box
// (as opposed to the Cancel button).
public boolean bOk;
// The following components hold the text that the user
// entered into the visible text fields.
public JTextField name;
public JTextField publication;
public JTextField address;
public JTextField round;
public JTextField phone;
public void actionPerformed (ActionEvent e)
// If the user pressed the Ok button, indicate this
// by assigning true to bOk.
if (e.getActionCommand ().equals ("Ok"))
bOk = true;
// Destroy the dialog box and return to the point
// just after the creation of the DataEntryForm object.
dispose ();
public DataEntryForm (JFrame parent, String title)
// Call the other constructor. The current constructor
// is used for insert operations. The other constructor
// is used for update operations.
this (parent, title, "", "", "", "", "");
public DataEntryForm (JFrame parent, String title,
String name, String publication,
String address, String round,
String phone)
// Initialize the superclass layer.
super (parent, title, true);
// Choose a grid bag layout so that components can be more
// accurately positioned. (It looks nicer.)
setLayout (new GridBagLayout ());
// Add appropriate first name, last name, phone, fax, and
// email components to the current DataEntryForm container.
// (Remember, DataEntryForm is a subclass of Dialog.
// Dialog is a container. Therefore, DataEntryForm
// inherits the ability to be a container.)
addComponent (this, new JLabel ("Name: "), 0, 0, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.WEST);
this.name = new JTextField (15);
addComponent (this, this.name, 1, 0, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
if (title.equals ("Update"))
this.name.setText (name);
addComponent (this, new JLabel ("Publications: "), 0, 1, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.WEST);
this.publication = new JTextField (15);
addComponent (this, this.publication, 1, 1, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
if (title.equals ("Update"))
this.publication.setText (publication);
addComponent (this, new JLabel ("Address "), 0, 2, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.WEST);
this.address = new JTextField (15);
addComponent (this, this.address, 1, 2, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
if (title.equals ("Update"))
this.address.setText (address);
addComponent (this, new JLabel ("Round No "), 0, 3, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.WEST);
this.round = new JTextField (15);
addComponent (this, this.round, 1, 3, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
if (title.equals ("Update"))
this.round.setText (round);
addComponent (this, new JLabel ("Phone Number "), 0, 4, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.WEST);
this.phone = new JTextField (15);
addComponent (this, this.phone, 1, 4, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
if (title.equals ("Update"))
this.phone.setText (phone);
addComponent (this, new JLabel (""), 0, 5, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
addComponent (this, new JLabel (""), 1, 5, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
JButton b;
// Add an Ok button to this container.
addComponent (this, b = new JButton ("Ok"), 0, 6, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
b.addActionListener (this);
// Add a Cancel button to this container.
addComponent (this, b = new JButton ("Cancel"), 1, 6, 1, 1,
GridBagConstraints.NONE,
GridBagConstraints.CENTER);
b.addActionListener (this);
// Set the size of the dialog window to 250 pixels
// horizontally by 200 pixels vertically.
setSize (250, 200);
// Do not allow users to resize the dialog window.
setResizable (false);
// Make sure that the dialog window is visible.
setVisible (true);
private void addComponent (Container con, Component com,
int gridx, int gridy,
int gridw, int gridh, int fill,
int anchor)
// Get the current layout manager. It is assumed to
// be a GridBagLayout object.
LayoutManager lm = con.getLayout ();
// Create a GridBagConstraints object to make it
// possible to customize component positioning.
GridBagConstraints gbc = new GridBagConstraints ();
// Assign the x and y grid positions.
gbc.gridx = gridx;
gbc.gridy = gridy;
// Assign the number of grid blocks horizontally and
// vertically that are occupied by the component.
gbc.gridwidth = gridw;
gbc.gridheight = gridh;
// Specify the component's resize policy (fill) and
// the direction in which the component is positioned
// when its size is smaller than available space (anchor).
gbc.fill = fill;
gbc.anchor = anchor;
// Set the new constraints that the grid bag layout
// manager will use.
((GridBagLayout) lm).setConstraints (com, gbc);
// Add the component to the container.
con.add (com);
// ===========================================================
// Class: MsgBox
// This class displays a message box to the user. The message
// is usually an error message. The user must press the Ok
// button to terminate the message box.
// ===========================================================
class MsgBox extends JDialog implements ActionListener
public void actionPerformed (ActionEvent e)
// Terminate the dialog box in response to the user
// pressing the Ok button.
dispose ();
public MsgBox (JFrame parent, String title, String msg)
// Initialize the superclass layer.
super (parent, title, true);
// Store the msg argument in a Label object and add
// this object to the center part of the dialog window.
JLabel l = new JLabel (msg);
add ("Center", l);
// Create a Button object and add it to the south part
// of the dialog window.
JButton b = new JButton ("Ok");
add ("South", b);
// Make the current object a listener to events that
// occur as a result of the user pressing the Ok
// button.
b.addActionListener (this);
// Make sure that the Ok button has the focus.
b.requestFocus ();
// Do not allow users to resize the dialog window.
setResizable (false);
// Allow the layout manager to choose an appropriate
// size for the dialog window.
pack ();
// Make sure that the dialog window is visible.
setVisible (true);
}

Difference between extends and implements

hi
i am new to java. i need to know the difference between extends class implement class.
can anybody explain in simple words? i am new too oops concept also?
what are the conditions to use extends class, implement and interface?
class b extends a implements c
i know class a is a super class and class b is a sub class.
if class b extends class a means how should be the class a, what about the methods?
and class a implements class c means what should be the conditions?
i searched in Internet but the explanation is not very to me.can body explain me please?
thank you

sarcasteak wrote:
Your class can implement an interface, which means it must use the methods defined in the interface.No, it doesn't need to use them. It needs to implement them. Or be declared abstract.
Note that the methods in the interface are empty,No, they're not. They're abstract.
// empty method
void foo() {}
// abstract method
abstract void foo();(The abstract keyword is optional for interface methods, since they're all abstract.
and you have to define what they do in your class that implements the interface.Just like they have to for abstract methods in a class you extend, if the child class is not declared abstract.
There really isn't any difference between "extends" and "implements." There is no situation where you can choose. Any case where one is legal, only that one is legal. They could just as easily be a single keyword.
Presumably the OP's real question is, "When do I use a class for a supertype vs. using an interface for a supertype?" The answer to that, of course, is:
Use a class when at least some of the methods have valid default implementations. Use an interface when that is not the case. And of course the two are not mutually exclusive. It's quite common to do both.
At the end of the day, an interface is really nothing more than a class that has no non-final or non-static member variables and whose instance methods are all abstract, and from which you can multiply inherit.
Edited by: jverd on Feb 4, 2010 1:56 PM

Whatz the difference between jdk and jre

i would like to know the difference between jdk and jre.

Yes JRE is Java Run Time Environment. The java programming language adds the portability by converting the source code to byte code version which can be interpreted by the JRE and gets converted to the platform specific executable ones. Thus for different platforms one has corresponding implementation of JRE. But JRE has to meet the specification JVM (Java Virtual Machine) Concept that serves as a link between the Java libraries and the platform specific implementation of JRE. Thus JVM helps in the abstraction of inner implementation from the programmers who make use of libraries for their programmes.
The JDK(Java Developmental Tool kit) comes along with java libraries and JVM embedded in it. Apart from these it comes along with the utility tools for byte code compilation "javac", Executing the byte codes through java programmes through "java" and many more utilities found in the binary directory of java. Speaking practically JDK is essential for developers, which comes along with library packages to develop Software programmes. While JRE is minimal set of programmes which executes the java class files developed by the software developers.

Inter face and abstract class

hi
can u please tell me the difference between interface and an abstract class? In which situations they will be usefull.
thank u
shyam

http://java.sun.com/developer/JDCTechTips/2001/tt1106.html#tip2

Difference between GUI_UPLOAD and WS_UPLOAD

Hi,
Please make me clear about the difference between GUI_UPLOAD and WS_UPLOAD. In which cases we need to use these modules...??
Thanks,
Satish

I would suggest to always use the GUI_UPLOAD. I say this because this is the function module which is used in the GUI_UPLOAD method of the class CL_GUI_FRONTEND_SERVICES.   Really, you should probably use the class/method instead of the function module.
data: filename type string.
filename = p_file.
call method cl_gui_frontend_services=>gui_upload
         exporting
              filename                = filename
              filetype                = 'ASC'
         changing
              data_tab                = iflatf
         exceptions
              file_open_error         = 1
              file_read_error         = 2
              no_batch                = 3
              gui_refuse_filetransfer = 4
              no_authority            = 6
              unknown_error           = 7
              bad_data_format         = 8
              unknown_dp_error        = 12
              access_denied           = 13
              others                  = 17.
Regards,
Rich Heilman

Difference between BAPI and RFC?

Difference between BAPI and RFC?
also where to use BAPI and where to use RFC?

Hi,
BAPI are RFC enabled function modules. the difference between RFc and BAPI are business objects. You create business objects and those are then registered in your BOR (Business Object Repository) which can be accessed outside the SAP system by using some other applications (Non-SAP) such as VB or JAVA. in this case u only specify the business object and its method from external system in BAPI there is no direct system call. while RFC are direct system call Some BAPIs provide basic functions and can be used for most SAP business object types. These BAPIs should be implemented the same for all business object types. Standardized BAPIs are easier to use and prevent users having to deal with a number of different BAPIs. Whenever possible, a standardized BAPI must be used in preference to an individual BAPI.
The following standardized BAPIs are provided:
Reading instances of SAP business objects
GetList ( ) With the BAPI GetList you can select a range of object key values, for example, company codes and material numbers.
The BAPI GetList() is a class method.
GetDetail() With the BAPI GetDetail() the details of an instance of a business object type are retrieved and returned to the calling program. The instance is identified via its key. The BAPI GetDetail() is an instance method. BAPIs that can create, change or delete instances of a business object type
The following BAPIs of the same object type have to be programmed so that they can be called several times within one transaction. For example, if, after sales order 1 has been created, a second sales order 2 is created in the same transaction, the second BAPI call must not affect the consistency of the sales order 2. After completing the transaction with a COMMIT WORK, both the orders are saved consistently in the database.
Create( ) and CreateFromData! ( )
The BAPIs Create() and CreateFromData() create an instance of an SAP business object type, for example, a purchase order. These BAPIs are class methods.
Change( )
The BAPI Change() changes an existing instance of an SAP business object type, for example, a purchase order. The BAPI Change () is an instance method.
Delete( ) and Undelete( ) The BAPI Delete() deletes an instance of an SAP business object type from the database or sets a deletion flag.
The BAPI Undelete() removes a deletion flag. These BAPIs are instance methods.
Cancel ( ) Unlike the BAPI Delete(), the BAPI Cancel() cancels an instance of a business object type. The instance to be cancelled remains in the database and an additional instance is created and this is the one that is actually canceled. The Cancel() BAPI is an instance method.
Add<subobject> ( ) and Remove<subobject> ( ) The BAPI Add<subobject> adds a subobject to an existing object inst! ance and the BAPI and Remove<subobject> removes a subobject from an object instance. These BAPIs are instance methods.
Regards,
Prakash

Difference between path and classpath

Difference between path and classpath?

PATH - set of paths there executables will be found.
CLASSPATH - set of paths and archives there class files will be found.

What is the difference between ws_upload and gui_upload

what is the difference between ws_upload and gui_upload
what is the difference between ws_download and gui_down load
pls tell briefly

Hi Kuamr,
UPLOAD and DOWNLOAD, the function modules used until now are not part of the standard set of ABAP commands. They are used to display the file interface on the presentation server. UPLOAD and DOWNLOAD are not compatible with USs and have been replaced by GUI_UPLOAD and GUI_DOWNLOAD.
The new function modules, GUI_UPLOAD and GUI_DOWNLOAD, have an interface that also allows you to write Unicode format to the local hard drive. For a description of these interfaces, refer to the documentation for each function module, available under SAP Easy Access " Development " Function Builder " Goto " Documentation.
Instead of using the function modules, you can use the static methods GUI_UPLOAD and GUI_DOWNLOAD of the global class CL_GUI_FRONTEND_SERVICES.
Hope this resolves your query.
Reward all the helpful answers.
Regards

Difference between inheritance and abstract class

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