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What an abstract class in java ? and what is an interface in java ? please give examples if possible

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  • sumitnxt Nov 18, 2009

    great.. thanks


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An abstract class is a class that is declared abstract—it may or may not include abstract methods. Abstract classes cannot be instantiated, but they can be subclassed. An abstract method is a method that is declared without an implementation (without braces, and followed by a semicolon), like this:
abstract void moveTo(double deltaX, double deltaY);
If a class includes abstract methods, the class itself must be declared abstract, as in: public abstract class GraphicObject {
// declare fields
// declare non-abstract methods
abstract void draw();
When an abstract class is subclassed, the subclass usually provides implementations for all of the abstract methods in its parent class. However, if it does not, the subclass must also be declared abstract.

In the Java programming language, an interface is a reference type, similar to a class, that can contain only constants, method signatures, and nested types. There are no method bodies. Interfaces cannot be instantiated—they can only be implemented by classes or extended by other interfaces. Extension is discussed later in this lesson. Defining an interface is similar to creating a new class:
public interface OperateCar {

// constant declarations, if any

// method signatures
int turn(Direction direction, // An enum with values RIGHT, LEFT
double radius, double startSpeed, double endSpeed);
int changeLanes(Direction direction, double startSpeed, double endSpeed);
int signalTurn(Direction direction, boolean signalOn);
int getRadarFront(double distanceToCar, double speedOfCar);
int getRadarRear(double distanceToCar, double speedOfCar);
// more method signatures
Note that the method signatures have no braces and are terminated with a semicolon. To use an interface, you write a class that implements the interface. When an instantiable class implements an interface, it provides a method body for each of the methods declared in the interface. For example,
public class OperateBMW760i implements OperateCar {

// the OperateCar method signatures, with implementation --
// for example:
int signalTurn(Direction direction, boolean signalOn) {
//code to turn BMW's LEFT turn indicator lights on
//code to turn BMW's LEFT turn indicator lights off
//code to turn BMW's RIGHT turn indicator lights on
//code to turn BMW's RIGHT turn indicator lights off

// other members, as needed -- for example, helper classes
// not visible to clients of the interface

In the robotic car example above, it is the automobile manufacturers who will implement the interface. Chevrolet's implementation will be substantially different from that of Toyota, of course, but both manufacturers will adhere to the same interface. The guidance manufacturers, who are the clients of the interface, will build systems that use GPS data on a car's location, digital street maps, and traffic data to drive the car. In so doing, the guidance systems will invoke the interface methods: turn, change lanes, brake, accelerate, and so forth.
I hope this helps and good luck!
what an abstract class in - 22e7160.png

Posted on Nov 18, 2009

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Can you give me examples of abstact nouns

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What difference between genricServlet and httpServlet

public abstract class GenericServlet extends java.lang.Object implements Servlet, ServletConfig,
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May 12, 2011 | Computers & Internet

1 Answer

Good morning,i have to make minor prjt in java.

The simplest basic java is the hello world ! example.
class myfirstjavaprog
public static void main(String args[])
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Aug 31, 2009 | Microsoft Windows XP Professional

1 Answer

Javac unable to compile java error or batch file?

first of all you have to set path for your jdk
have you done that???????

if not then go to and search for that vedio.

if yes, then i think you have not named the project properly

when you are to save your project, name it in the "name of the main"

for example:

class Manju
   public static void main(String arg[]s)

save it as and then compile

no matter what other classes are being related to the project.

this much i only know

if you wanna contact me or chat with me, my email id is

May 16, 2009 | Microsoft Windows XP Professional

1 Answer

In cpp programming why do we go for abstract base class?

Virtual keyword allows the program to dynamically decide which function to call. That is, when derived class is inherited from a base class the function in derived class can perform a completely different action from the one in Base class. Hence the function call via a pointer or reference maps to different functions based on the type of the object.

Abstract base class is used, so that anyone who is inherting from this class should implement that interface. Because the base class may not have a meaningful implementation for that interface. For example to design a program for computing area of different shapes like rectangle, triangle, hexagon etc. base class can be thought of as Shape. In addition the base class can be made abstract by declaring Area to be a pure virtual function. Then the different shapes like Rectangle, Triangle classes can inherit from Shape and implement Area interface based on their formulae.

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4 Answers

Can anyone tell how run java program in cmd prompt???


You need to type:

If it's a program.class

java program

or of it's a program.jar

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Apr 03, 2009 | Sun Java Programming Language (cdj-275)

1 Answer

How to write jdbc connections


welcome_title_image.gif Java JDBC Tutorial Java JDBC Tutorial
The JDBC ( Java Database Connectivity) API defines interfaces and classes for writing database applications in Java by making database connections. Using JDBC you can send SQL, PL/SQL statements to almost any relational database. JDBC is a Java API for executing SQL statements and supports basic SQL functionality. It provides RDBMS access by allowing you to embed SQL inside Java code. Because Java can run on a thin client, applets embedded in Web pages can contain downloadable JDBC code to enable remote database access. You will learn how to create a table, insert values into it, query the table, retrieve results, and update the table with the help of a JDBC Program example.

Although JDBC was designed specifically to provide a Java interface to relational databases, you may find that you need to write Java code to access non-relational databases as well.
JDBC Architecture jdbc.jpg Java application calls the JDBC library. JDBC loads a driver which talks to the database. We can change database engines without changing database code.
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java.sql package.
import java.sql.*; The star ( * ) indicates that all of the classes in the package java.sql are to be imported.
1. Loading a database driver,
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2 Answers

StartActivity fails to launch class called

This example is working try it.

import android.content.ActivityNotFoundException;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
public class Forwarding extends Activity
protected void onCreate(Bundle savedInstanceState)
Button goButton = (Button)findViewById(;
goButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
try {
Intent intent = new Intent();
intent.setClass(Forwarding.this, ForwardTarget.class);
} catch(Exception e) {


import android.os.Bundle;
public class ForwardTarget extends Activity
protected void onCreate(Bundle savedInstanceState)



<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android=""
<application android:icon="@drawable/icon" android:label="@string/app_name">
<activity android:name=".Forwarding"
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
<activity android:name=".ForwardTarget"/>


<?xml version="1.0" encoding="utf-8" ?>

<LinearLayout xmlns:android=""
android:orientation="vertical" android:padding="4dip"
android:gravity="center_horizontal" android:layout_width="fill_parent"
<TextView android:layout_width="fill_parent"
android:layout_height="wrap_content" android:layout_weight="0"
android:paddingBottom="4dip" android:text="forwarding" />
<Button android:id="@+id/go" android:layout_width="wrap_content"
android:layout_height="wrap_content" android:text="go">
<requestFocus />


<?xml version="1.0" encoding="utf-8" ?>
<LinearLayout xmlns:android=""
android:orientation="vertical" android:padding="4dip"
android:gravity="center_horizontal" android:layout_width="fill_parent"
<TextView android:layout_width="fill_parent"
android:layout_height="wrap_content" android:layout_weight="0"
android:text="forward_target" />

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1 Answer


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You'll probably have to run this command with administrator privileges...not too familiar with Windows.

On a side note, if you use this approach, the example doesn't close any of the streams that were opened to read the output of the command issued. You should do this to avoid unwanted resource consumption.

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1 Answer

Schema classes and attributes

Every directory object you create is an instance of an object class contained in the schema. Each object class contains a list of associated attributes that determine the information the object can contain. Classes and attributes are defined independently, so that a single attribute can be associated with multiple classes. All schema classes and attributes are defined by the classSchema and attributeSchema objects, respectively.


ClassSchema objects are used to define classes in the schema. A classSchema object provides the template for building directory objects of that class. Examples of classSchema include User and Server. A classSchema object contains, among other things, the following information:
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Common name and Lightweight Directory Access Protocol (LDAP) display name

Lists of the "must contain" and "may contain" attributes for instances of the object

Relative distinguished name attribute

A list of possible parent classes

Class types

Three different types of classes exist in the schema:Class type Purpose

Used to instantiate objects (users, servers and so on) in the directory.

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Common name and LDAP display name

Syntax rules

Data constraints (single versus multivalued, minimum, and maximum values)

Whether and how the attribute is indexed

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