mcs-024 solved assignment

BCA 4 solved assignment(2014-2015)

mcs-024

Q-1 what is object oriented programming?explain features of object oriented programming  write a program in java to data hiding.

ansobject oriented programming is aprogramming methodoilogy where the main emphasis is given on the object or the data and not onthe onfunction or operations that operate on data data is undervaluedin procedural programming. here the design puts data upfront and organisation of data is significant area . access rights are reserved as well to protect data from accidental changes by an intruder.

features of oop-:

object-object is a collection of a number of entities.object take up space in the memory .object are instances of classes when a program is executed  the object interacted by sending messages to one another.each object contain data or code to manipulate the data object can interect without knowing the details of each other or code.

class-class is a collection of object of similar type.object are variable of the type class once a class has been defined we can create any number of objects belonging to that class. grapes banana andf orange are the member of the class.

Dynamic binding-refers to linking of the fiunction call with function defination is called binding and when it take palce at run time called dynamic binding.

Message passing-The process by which one object can interact with other object is called message pa.ssing

Inheritance-inheritance is the oops feature which allow derivation of the new object from the existing ones. it allows the creation of new class,called the derived class from the existing class called base class.inheritance allow the base class to be accessed by the derive class which in turn their new features in addition to the old base class feature.

Data abstraction and encapsulation-encapsulation is the principle by which related content of a system are kept together . it minimize trffic between different parts of the work and it seperates certain specific requirements  from other parts  of specification which use  those requirementsabstraction refers to the act of represting essential feature without including the background detail to distinguish object/functions from other object.  functional abstraction was provided by telling which task is performed by function and hiding how the task is performed.

Polymorphism- greek term means ability to take more than one form. An operation may exhibite different behaviours in different instances. The behaviour depends upon the types of data used in the operation.

Example

• Operator Overloading 
• Function Overloading

package DataHiding;

/**

 * This class illustrates basic data hiding concepts

 * @author nicomp

 */

public class Person {

//  public - a violation of data hiding 'rules'

    public int height;

//  private - not visible outside the class

    private float weight;

     

//  Here are 'get' and 'set' methods for the

//    private variable declared above.   

    public float GetWeight() { return weight;}

    public float SetWeight(float weight){

        if (weight >= 0)

            this.weight = weight;

        return this.weight;

    }

}

b)explain why java is platform independent.also explain how memory manage in java.

ans java is platform independent the meaning of platform here some combination of hardware and system software but here you can understand it as your operating system. java is compiled to an interdimiate form called java byte-code or simply byte code. a java program never really executes immediately after compilation on the host machine. rather this special program called java or java virtual machine reads the byte code ,translate it into the corresponding host machine instruction and then execute the machine instruction a java programing only run if the java virtual machine and some routines have been installed in the computer system.the second important part which make the java is portable is the elimination of hardware architecture dependent constructs

for ex integers  are always 4 bytes long and floating point variables follow the iEEE 754. you dont need to worry  that the interpretation of your integer is going to change if you move from one hardware to another hardware like pentinum to power pc.you devlope java program in any computer system and the execution  of that program is possible an any other computer system loaded with JVM.for ex you can write and compile the java program on windows 98 execute the compiled program on JVm machine of the macintosh  operating system .

In Java, memory is allocated only to objects. There is no explicit allocation of memory, there is only the creation of new objects. (Java even treats array types as objects.)

• In Java, it's easy to let go of an entire "tree" of objects by setting the reference to the tree's root to null; the garbage collector will then reclaim all the objects (unless some of the objects are needed elsewhere). This is a lot easier than coding each of the objects' destructors to let go of its own dependencies (which is a coding-level problem with C++).
• The Java runtime employs a garbage collector that reclaims the memory occupied by an object once it determines that object is no longer accessible. This automatic process makes it safe to throw away unneeded object references because the garbage collector does not collect the object if it is still needed elsewhere. Therefore, in Java the act of letting go of unneeded references never runs the risk of deallocating memory prematurely.

Q-2 (a) what is static method ?explain the application of static method with example.

(ans)A static method is a characteristic of the class not of the object it has created. static variable and methods are also known as class variable since each class method occurs once per class instance of a class or you can say every object is having its own copy of instance variable. a program can execute a static method without creating an object of the class.All other method must be invoked through an object must exit before they can be used.You have seen that every java application program has one main() method this method is always static because java starts execution from this main() method and the time no object is created

ex

import java.util.date;

class Date app

{public static void main(string args[])

{

Date today= new Date();

system.out.printin(today);

}

}

the point which should be noticed here is that the application never instanitiated the syustem class and that out is referred to directly from the class. this is because out is declared as a static variable:a variable associated with the clasds rather than with an instanceof the class.you can also associate methods with a class-static methods-using static keyword.
(b)what are different arithmetic and logical operator in java?write a java program and show uses of all arithmetic operator.
ans)Arithmetic operators are used in mathematical expressions in the same way that they are used in algebra. The following table lists the arithmetic operators:operators are divided into 2 categories unary operator and binary operator addition subtraction multiplication is abinary operator and applied  only on two operant.increment and decrement are unary operators and applied on single operand.let a=10  and b=5

Operator	Description	Example
+	Addition - Adds values on either side of the operator	a+b  will give 15
-	Subtraction - Subtracts right hand operand from left hand operand	a b- will give 5
*	Multiplication - Multiplies values on either side of the operator	a* b will give 50
/	Division - Divides left hand operand by right hand operand	a / b will give 2
%	Modulus - Divides left hand operand by right hand operand and returns remainder	a%b A will give 0
++	Increment - Increases the value of operand by 1	b++ gives 6
--	Decrement - Decreases the value of operand by 1

Logical operator-allow you to combine the resuylt of multiple expression to return a single value trhat evaluate to either true or false

Operator	Description	Example
&&	Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.	(A && B) is false.
||	Called Logical OR Operator. If any of the two operands are non-zero, then the condition becomes true.	(A || B) is true.
!	Called Logical NOT Operator. Use to reverses the logical state of its operand. If a condition is true then Logical NOT operator will make false.	!(A && B) is true

(c) what is final keyword in java?explain different uses of final keyword.

ans)final keyword-final keyword can be applied with the variable .once you make a reference you final you are not allowed to change that reference and compiler will verify this and raise compilation error if you try to reinitialize final variable in java

final keyword is used in

1. variable 
2. method
3. class

final variable- any final variable which modified as final keyword is known as final variable ex of final variable

class bike

final int speed limit=90;//final variable

void run(){

speed limit=400;

}

public static void main(sring args[ ]){

bike obj=new bike();

obj.run();

}

}//end of class-Java class with final modifier is called final class in java. Final class is complete in nature and can not be sub-classed or inherited. Several classes in Java are final e.g. String, Integer and other wrapper classes. Here is an example of final class in java

final class in java-

final class Bike{} 

class Honda extends Bike{ 

void run(){System.out.println("running safely with 100kmph");} 

 public static void main(String args[]){  

Honda honda= new Honda();

honda.run();

}

}

final method in java-Final keyword in java can also be applied to methods. A java method with final keyword is called final method and it can not be overridden in sub-class. You should make a method final in java if you think it’s complete and its behavior should remain constant in sub-classes. Final methods are faster than non-final methods because they are not required to be resolved during run-time and they are bonded on compile time. Here is an example of final method in Java:

1. class Bike{  
2. final void run(){System.out.println("running...");} 
3. } 
4. class Honda extends Bike{ 
5. public static void main(String args[]){  
6.  new Honda().run();
7. }
8. }

Q-3 what is  method overloading? how it is different from method overriding?write a java program to explain overloading and overriding of methods.

ans)two or more methodswhich are very similar in nature are required.forexample you can take methods area _s and area _ r in a class test in program of section 1.3 of this units. both the methods are finding area but the argument passed to them and theirf implementation is different. all the methods of similar kinds in a class can have the same name but remember all the methods will have different prototypes this conceptis known as method overloading

1.  class overload demo
   { 
            void triangleArea(float base, float height) 
            { 
                  float area; 
                  area = base * height / 2.0f; 
                  System.out.println(“Area = “ + Area);
            }
   
            void triangleArea(float side1, float side2, float side3) 
            { 
                     float area,s; 
                     s = (side1 + side2 + side3) / 2.0; 
                     area = Math.sqrt(s*(s-side1) * (s-side2) * (s-side3) ); 
                     System.out.println(“Area = “ + area);
            }
   }
   
   class MainOverloadDemo
   { 
               public static void main(String args[]) 
               { 
                       OverloadDemo ovrldDemo = new OverloadDemo(); 
                       ovrldDemo.triangleArea(20.12,58.36); 
                       ovrldDemo triangleArea(63.12,54.26,95.24);
               } 
   }

overriding-subclass extending the parent class has access to all the non-private data members and methods its parent class and adding new methods is to extend the behaviour of the parent class.however sometimes it is required to modify the behaviour of parent class . to modify the behaviour of the parent class overriding is use
SOME IMPORTANT POINTS THAT MUST BE TAKEN CARE WHILE OVERRIDING A METHOD:

• AN OVERRIDING METHOD(LARGELY) REPLACES THE METHOD IT OVERRIDES.
• Each methods must have exactly the same arguments lists, both in type and in order.
• overriding method must have exactly the same return type as the method it overrides
• each method in parent class can be overridden at most once in any one of the subclass.
• overriding is associated with inheritance.

class Super 
{
     int sum;
     A(int num1, int num2) 
     {
             sum = a+b;
     }
     void add() 
     {
            System.out.println("Sum : " + sum);
     }
}
class Sub extends Sub 
{
       int subSum;
       Sub(int num1, int num2, int num3) 
       {
               super(num1, num2);
               subSum = num1+num2+num3;
       }
       void add() 
       {
               super.add();
               System.out.println("Sum of 3 nos : " +subSum);
       }
}

b)what is abstract class ? why abstract class use in java with the help of example program.
ans)when we extending an existing class we have a choice whether to redefine the methods of the super class.basically a superclass has common features that are shared by subclasses. in some cases you will find that superclass can not have any instance(object) and such classes are abstract class .abstract classes usually contain abstracts method.Abstract method is a method signature(declaration) without any implementation .basically this abstract methods provide a common interface derived classes.you know a super class is more general than its subclasses.the super class contains elements and propertiescommon to all of the subclasss.often, the superclass will be setup as an abstract class, which does not allow object of its prototype to be created.in thius case only objects of the subclass are created. to do this the reserved word abstract is included(prefixed) in the class defination.

1. public abstract class player //class is abstract
2. {
3. name=vname;
4. }
5. public string getname() //regular method
6. {return (name);
7. }
8. public abstract void play();
9. //abstract method: no implementation

}
Q-4 what is inheritance?explain different type of inheritance supported by  java.
ans)inheritance is a language property specific to the object-oriented paradigm.inheritance is used for a unique form of code -sharing by allowing you take the implementation of any given class and build a new class  based on that implementation.let us say class b, starts by inheriting all of the data and operations defined in the class a. this new subclass can extend the behaviour by adding additional data and new methods to operate on it. basically during programming inheritance is usedfor extending the existing property of as class. in other words it can be said that inheritance is"from generalization -to -specialization".in this by using general class,class with specific properties can be defined.
different type of inheritance supported by java

1. single inheritance-when a class extend another one class only then we  call it a single inheritance.
   

ex single inheritance

Class C
{
   public void methodC()
   {
     System.out.println("Base class method");
   }
}

Class E extends C
{
   public void methodE()
   {
     System.out.println("Child class method");
   }
   public static void main(String args[])
   {
     B obj = new B();
     obj.methodC(); //calling super class method
     obj.methodE(); //calling local method
  }
}

2 Multilevel inheritance-:refers to a mechanism in OOp technology where one can inherit from a derived class, thereby making this derived class the base class for the new class. 

ex of multilevel inheritance

Class A
{
   public void methodA()
   {
     System.out.println("Class A method");
   }
}
Class B extends A
{
public void methodB()
{
System.out.println("class B method");
}
}
Class C extends B
{
   public void methodC()
   {
     System.out.println("class C method");
   }
   public static void main(String args[])
   {
     C obj = new C();
     obj.methodA(); //calling grand parent class method
     obj.methodB(); //calling parent class method
     obj.methodC(); //calling local method
  }
}

3 Hierarchical inheritance-:one class is inherited by many sub classes. In below example class B,C and D inherits the same class A. A is parent class (or base class) of B,C & D. 

Class w
{
  public void methodA()
  {
     System.out.println("method of Class w");
  }
}
Class x extends w
{
  public void methodx()
  {
     System.out.println("method of Class x");
  }
}
Class y extends w
{
 public void methodC()
 {
 System.out.println("method of Class y");
 }
}
Class z extends w
{
  public void methodD()
  {
    System. out.println("method of Class z");

  }
}
Class MyClass
{
  public void methodx()
  {
     System.out.println("method of Class x");
  }
  public static void main(String args[])
  {
     x obj1 = new x();
     y obj2 = new y();
     z obj3 = new z();
     obj1.methodw();
     obj2.methodw();
     obj3.methodw();
  }
}

b)what is an exception?explain how is exception is handled in java.create your own exception class to handle undesirable operation in your program.

ans)An exception condition is considered as a problem, which stops program execution from continuation from point of occurence of it . Exception stops  you from continuing because of lack of information to deal with the exception condition.in other words it is known what to do in specific conditions.

Exception in java are handled by the use of these five keywords:try,catch,throw,throws and finally.you have to put these statement s of program on which you want to monitor for exception, in try to block.

Using try catch-:to catch an exception in java you write a try block with one or more catch clauses.Each catch clause specifies one exception type that it is prepared to handle.The try block places a fence around the code that is under thye watchful eye of the associated catcher.if the bit of code delimited by the try block throws an exception, the associated catch clause that is prepared to handle the thrown exception,the program continues execution starting with first statement of the catch

clause and the catch block is used to execuring code to handle exception and graceful termination of the program.

public class Excep_test

{

public static void main(string[] args)

{try{int data[]={2,3,4,5};

system.out.printin("value at:"+data[4]);

}catch(arrayindexoutofboundsexception e)

{

system.out.printin("sorry you are trying to print beyond the size of data[]");

}}}

output

sorry you are trying to print beyond the size of data[]

catch of multiple exception-:some time there may be a chance to have multiple exceptions in a program. you can use multiple catch clauses to catch the different kinds of exception in a program . you can use multiple catch clauses to catch the different kinds of exception us raised by a block of code, then to handle these exception more than one catch clauses are used. when an exception is throw in different  catch blocks associated with try block inspect in order and the first one whose type matches with the exception type is executed this code snippet will give you an idea how to catch multiple exceptions.
public class multicatch
{
public static void main(string[] args)
{
int repeat;
try
{
repeat=integer.parseint(args[0]);
}
catch(arrayindexoutofboundsexception e)
{
//pick a default value for repeat
repeat=1;
}
catch(numberformatexception e)
{
//print an error message
system.err.printin("usage:repeat as count");
system.err.printin("where repeat is the number of times to say hello java");
system.err.printin("and given as an integer like 2 or 5");
return;
}
for(int i=0;i<repeat;i++0
{
system.out.printin("hello");
}
}
}
output
hello
Using finally clause-: there are several ways of exiting from a block of code(the statement between two matching curly braces).once a jvm has begun to execute a block, it can exit that block in any of several waysit could for example simply exit after reaching the closing curly brace.it could encounter to break,continue,or return statements that causes it to jump out of the block from somewhere in the middle.let us take an example of opening a file in a method. you open the file perform needed operation on the file and most importantly you want  to ensure that the file gets closed no matter how the method completes.in java,this kind of desires are fullfilled with the help of finallly clause.
public class Finally_test
{
public static void main(string[]args)
{
try
{
system.out.printin("hello"+args[0]);
}
catch(arrayindexoutofboundsexception e)
{
system.out.printin("Hello,you are here after arrayindexoutof boundsexception")P;
} 
finally
{
system.out.printin("finally you have to reach here");
}
}
}
output
hello,you are here arrayindexoutofboundsexception
finally you have to reach here
Q-5b)what is string class in java?explain different constructor and method of string class also write a java program to find length of the given string.
ans)java provided two calssesfor handling string values ,which are string.the string class is provided for string whose value will not change.for ex in program you write a method that requires string data and it is not going to modify the string. the string buffer class is used for string that will be modified.string buffers are generally used for constructing character  data dynamically,for ex when you need to store information which may change.
the string class constructor:

1. public string():used to create a string object that represent an emptyy character sequence.
2. public string(string value):used to create a string object that represent the same sequence of characters as the argument;in other words,newly created string is a copy of the string passed an argument
3. public string(char value[]):new object of string is created using the sequence of characters from a sub-array of the character array argument.
4. public string(char value[],int offset,int count):a new string object created contains character from a sub array of the character array argument.
5. public string(byte bytes[],string enc)throws unsupported encoding exception:used to construct a new string by converting the specified array of bytes using the specified character encoding
6. public string(byte bytes[],int offset,int length):used to create an object of string by converting the specified sub array of bytes using the platform default character encoding.
7. public string(byte bytes[]):used to create an object of string by converting the specified array of bytes using the platform default character encoding.
8. public string(string Buffer buffer): used to create an object of string by using existing string buffer object which is passed as arguments.

 
public class StringLengthExample {
 
  public static void main(String[] args) {
    //declare the String object
    String str = "Hello World";
   
    //length() method of String returns the length of a String.
    int length = str.length();
    System.out.println("Length of a String is : " + length);
  }
}
 
/*
Output of a program would be:
Length of a String is : 11

Q-6 what is multithreading ? write a java program to explain how concurrency control  is done .

ans)multithreaded programs support more than one concurrent thread of execution.this means they are able to simultaneously execute multiple sequences of instructions.Each instruction sequence has its own unique flow of control that is independent of all others .these independently executed instruction sequence are known as threads.in single processor system only a single thread of execution occurs at a given instant . but multiple threads in a program  increase the utilization of cpu.The cpu quickly switches back and the forth between several threads to create an illusion that the threads are executing at the same time.you that single system processor support logical concurrency only.physical concurrency is not supported by it logical concurrency is the characteristics exhibited when multiple threads execute with separate ,independent flow of control.on the other hand on a multiprocessor system, several threads can execute at the same time and physical concurrency is achieved.
the advantage of multithreaded programs is that they support logical concurrency. many programming languages support multiprogramming, as it is the logically concurrent execution of multiple prrograms.for ex a program can request the operating system to execute the program A,B and C  by having it spawn a aeperate process for each program.these program can run in concurrent manner,depending upon the multi programming features supported by the underlying operating system.

b)what is i/o stream in java?explain what is byte stream? how byte stream is different from character stream.
ans)java input and output  is based on the use of streams .or sequences of bytes that travel from a source to a destination over a communication path. if the program is writing to a stream you can consider it as a stream source.if it is reading from a stream it is the stream destination.
an input stream represent a stream of data from which data can be read . again, this stream will be either directly connected to a device or else another stream.
an output stream represent a stream to which dadta can be written . Typically this stream will either be directly connected to device such as a file a network connection or to another output stream.
byte streams carry integers with values that range from 0 to 255. a diversified data can be expressed in byte format including numerical data executable programs and byte codes-the class file that runs a java program.
character stream are specialized type of byte stream that can handle only textual data. most of the functionallity available for byte streams is also provided for character streams.the methods for character streams generally accept parameters of datatype  char,while byte stream work with byte data types. the names of the methods in both sets of classes are almost identical except for the suffix,that is character-stream classes end with the suffix reader or writer and byte stream classes end with the suffix input stream and  output stream.
Q-7 a)What is Java Applet? Create an Applet program to display
your details including your academic and personal information. Use appropriate GUI components and images to make your applet more attractive and informative.
ans) The Applet class is packed in the Java. Applet package which has several interfaces.These interfaces enable the creation of Applets, interaction of Applets with the browser, and playing audio clips in Applets. In Java 2, class Javax.swing. J Applet is used to define an Applet that uses the Swing GUI components.As you know, in Java class hierarchy Object is the base class of Java.lang package.
The Applet is placed into the hierarchy as follows:

Java Applets are essentially Java programs that run within a web page. Applet

programs are Java classes that extend the Java.Applet.Applet class and are embedded

by reference within a HTML page. You can observe that when Applets are combined

with HTML, they can make an interface more dynamic and powerful than with

HTML alone. While some Applets do nothing more than scroll text or play

animations, but by incorporating these basic features in web pages you can make

them dynamic. These dynamic web pages can be used in an enterprise application to

view or manipulate data coming from some source on the server.

b)What are principles of event delegation model?Explain different sources of events and event listener.

ans) This model allows special classes, known as “adapter classes” to be built and be registered with a component in order to handle certain events. Three simple steps are required to use this model:

1. Implement the desired listener interface in your adapter class. Depending on

what event you’re handling, a number of listener interfaces are available. These

include: ActionListener, WindowListener, MouseListener,

MouseMotionListener, ComponentListener, FocusListener, and

ListSelectionListener.

2. Register the adapter listener with the desired component(s). This can be in theform of an add XXX Listener () method supported by the component for example include add ActionListener (), add Mouse Listener (), and add FocusListener ().

3. Implement the listener interface’s methods in your adapter class. It is in this

code that you will actually handle the event. The event delegation model allows the  developer to separate the component’s display (user interface) from the event handling (application data) which results in a cleaner and more object-oriented design

AWT provides two conceptual types of events: Semantic and Low-level events.

Semantic event : These are defined at a higher-level to encapsulate the semantics of

user interface component’s model.

Now let us see what the various semantic event classes are and when they are

generated:

An ActionEvent object is generated when a component is activated.

An Adjustment Event Object is generated when scrollbars and other adjustment

elements are used.Low-Level Events: These events are those that represent a low-level input or

windows-system occurrence on a visual component on the screen.

The various low-level event classes and what they generate are as follows:

• A Container Event Object is generated when components are added or

removed from container.

• A Component Event object is generated when a component is resized moved

etc.

• A Focus Event object is generated when component receives focus for input.

• A Key Event object is generated when key on keyboard is pressed, released

etc.

• A Window Event object is generated when a window activity, like maximizing

or close occurs.

• A Mouse Event object is generated when a mouse is used.

• A Paint Event object is generated when component is painted

Event Listeners: An object delegates the task of handling an event to an event

listener. When an event occurs, an event object of the appropriate type (as explained

below) is created. This object is passed to a Listener. The listener must implement

the interface that has the method for event handling. A component can have multiple

listeners, and a listener can be removed using remove Action Listener () method.

You can understand a listener as a person who has listened to your command and is

doing the work which you commanded him to do so.The semantic listener

interfaces defined by AWT for the above-mentioned semantic events are:

• ActionListener

• Ajdjustment  Listener

• ItemListener

• TextListener

The low-level event listeners are as follows:

• ComponentListener

• ContainerListener

• FocusListener

• KeyListener

• MouseListener

• MouseMotionListener

• Windows Listener

Q8 a)What is InetAddress class in Java ? Explain its methods and their uses.

ans)This class is used for encapsulating numerical IP address and domain name for that address.Because InetAddress is not having any constructor, its objects are created by using any of the following three methods static InetAddress getLocalHost() throws UnknownHostException: returns the InetAddress object representing local host static InetAddress getByName() throws UnknownHostException:

returns the InetAddress object for the host name passed to it. static InetAddress getAllByName() throws UnknownHostException: returns an arrayof InetAddresses representing all the addresses that a particular name is resolves to.

b)What is RMI? Explain architecture of RMI.

ans)Java provides RMI (Remote Method Invocation), which is “a mechanism that allows Advance Java

one to invoke a method on an object that exists in another address space. The other

address space could be on the same machine or a different one. The RMI mechanism

is basically an object-oriented RPC mechanism.”

RPC (Remote Procedure Call) organizes the types of messages which an application

can receive in the form of functions. Basically it is a management of streams of data

transmission.

RMI applications often comprised two separate programs: a server and a client.

A typical server application creates some remote objects, makes references to them

accessible, and waits for clients to invoke methods on these remote objects.

A typical client application gets a remote reference to one or more remote objects in

the server and then invokes methods on them.

RMI provides the mechanism by which the server and the client communicate and

pass information back and forth. Such an application is sometimes referred to as a

distributed object application.

RMI ARCHITECTURE-:

1. Stub/Skeleton layer – client-side stubs and server-side skeletons.

2. Remote reference layer-invocation to single or replicated object

3. Transport layer-connection set up and management, also remote object tracking

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