Java Youth

2012-10-20T21:47:00.001-07:00

Tutorial #11

Friends lets start this tutorial with an unusual topic called as Autoboxing, Unboxing & Annotation .

** Autoboxing & Unboxing
These features are being introduced in J2SE 5.0, & facilitates the process of handling primitive data types in
collections.We can use this feature to convert primitive data types to wrapper class types automatically.

The compiler generates a code implicitly to convert primitive type to the corresponding wrapper class type &

vice-versa.
       For example
               Double d_object = 100.2;
               double d_primitive = d_object.doublevalue( );
       Using autoboxing or unboxing feature, we can rewrite the baove code as :
                Double d_object = 100.2;
                double d_primitive = d_object ;

But , java compiler provides restrictions to perform the following conversation:-

Convert from null type to any primitive type.
Convert to the null type other than the identify conversation.
Convert from any class type C to any array type if C is not object.

** Annotation

     It is also known as metadata. This feature is mainly used to merge additional Java elements with

programming elements such as class, methods, local variable, package & fields.
               Metadata is stored in java class file by the compiler & these class files are used by the JVM or by
the program to find the metadata for interacting with the programming elements. A nice definition is given by
Wikipedia about annotation http://en.wikipedia.org/wiki/Java_annotation .This link provide a nice concept
about annotation with various examples related to each types of annotation .

While using annotations, we need to follow some guidelines:

Do not use extends clause, It automatically extends the marker interface java.lang.annotation.Annotation
Do not use any parameter for a method
Do not use generic methods
Do not use throws clause.

Lets consider an example on annotations:-
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import java.lang.annotation.*; 

import java.lang.reflect.*; 

@Retention (RetentionPolicy.RUNTIME) 

@interface MySingle 

{ 

    int value() ;  //this variable name must be value 

} 

public class single 

{ 

    //annotate a method using a marker 

    @MySingle (100) 

    public static void MyMeth () 

    { 

        single ob = new single (); 

        try

        { 

            Method m = ob.getClass().getMethod("MyMeth") ; 

            MySingle anno = m.getAnnotation(MySingle.class) ; 

            System.out.println("The value is :"+anno.value());  //displays 100           

        } 

        catch (NoSuchMethodException exc) 

        { 

            System.out.println("Method not found"); 

        } 

    } 

    public static void main (String args[]) 

    { 

        MyMeth(); 

    } 

}

To download this example in .java format that can run on eclipse by just pasting
the file in .src directory is given below:-

https://www.dropbox.com/s/u8y1qlay6mdsgw9/single.java
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___________________________________________________________________________________

** Interfaces : Multiple inheritance:-
     An interface is basically a kind of class. Like classes , interfaces contain methods & variables but with a
major difference. The difference is that interfaces define only abstract methods & final fields. This means
that interfaces do not specify any code to implement these methods & data fields contain only constants.
Therefore, it is responsibility of the class that implement an interface to define the code for implementation of
this method.
   Syntax-
   interface Interface_name
{
   varaible declaration;
   method declaration;
   }

Here variables are declared as follows:-
   static final type Variable_name = value ;
            & method is defined as given below :-
                       return-type methodName1 (parameter_list) ;

   Note :- Differences between Class & Interface:-

The member of the class can be constant or variables	Te member of an interface are always declared as constant, i.e=>their values are final
The class definition can contain the code for each of its methods	The method of an interface are abstarct in nature i.e=> there is no code associated with them . It is later defined by the class that implement the interface.
It can implement by declaring objects	It can-not be used to declare objects. It can only be inherited by a class.
It can use various access specifiers like public, private , or protected	It can only use public access specifier.

** Extending Interfaces
    Like classes interfaces can also be extended. That is , an interface can be sub-interfaced from other
interfaces. The new sub-interface will inherit all the members of the superinterface in a manner simplar to the
subclasses.
Syntax :-
                 interface name2 extends name1
                 {
   body of name2
                  }

         For eaxmple =>
   interface ItemConstants
   {
int code = 100 ;
string name = "fan" ;
   }
             interface item extends ItemConstants
             {
                      void display( ) ;
             }
Note that variable name & code are declared like simple variables because all the variables in an inetrface

are treated as a constants although the keyword final & static are not present.

                  We can also combine several interfaces together into one interface. For example the following
declaration is valid:-
   interface ItemConstants
   {
int code = 100 ;
string name = "fan" ;

   }
             interface itemMethods
             {
                      void display( ) ;

             }
   interface Item extends ItemConstants , itemMethods
   {
   -----------------------
   -----------------------
}

While interfaces are allowed to extend other interfaces, sub-interfaces cannot be defined the methods
declared in the superinterface.
          After all , subinterfaces are still interfaces , not classes. It is the responsibility of any class that
implement the derived interfaces to define all the methods.
   It is important to note that interface cannot extend class as it would violate the rule that an interface
can have only abstract methods & constants.

** Implementing interface
     Interfaces are used as "superclasses" whose properties are inherited by class who implement the interface
         Syntax:-
               class class_name implements interface_name
               {
   body of class_name
                }
     Here the class class_name is implementing the interface interface_name.
     A more general form of implementation may look like this:-
                class class_name extends supercalss
                      implements interface1 , interface2, ........
                {
body of class_name
                 }

Take one example to understand the above explained concept :-
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__________________________________________________________________________________

interface area 

{ 

    final static float pi = 3.14F ; 

    float compute(float x, float y); 

} 

class rectangle implements area 

{ 

    public float compute (float x, float y) 

    { 

        return (x*y); 

    } 

} 

class elipse implements area 

{ 

    public float compute (float x, float y) 

    { 

        return (pi*x*y); 

    } 

} 

class InterfaceTest 

{ 

    public static void main(String args[]) 

    { 

        rectangle rect = new rectangle(); 

        elipse cir = new elipse(); 

        area area1; 

        area1 = rect; 

        System.out.println("Area of rectangle="+ area1.compute(10,20)); 

        System.out.println("Area of elipse="+ area1.compute(10,35)); 

    } 

}

To download this example in .java format that can run on eclipse by

just pasting the file in .src directory is given below:-

https://www.dropbox.com/s/dgpttzj1fhseerg/InterfaceTest.java

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__________________________________________________________________________________

** Note:-
Any number of dis-similar classes can implement an interface. However to implement the methods, we
need to refer to the class objects as type of the interface rather than of their respective classes.
Note that if a class that implement an interface does not implement all the methods of the interface, then
the class becomes an abstract class & cannot be instantiated.

2012-10-12T09:59:00.001-07:00

Tutorial #10

In this tutorial we will try to understand the basic concept on Arrays, Strings & vectors that forms the backbone of the future topics that we are going to learn, as well as in the practical field of application development or web-development.

** Arrays
      An array is a group of contiguous or related data items that share a common name , mainly they contains
      element of same data-type, but inbuilt array-list in java also supports insertion of objects that may
      deoesn't belong to the same class .
   Types of arrays :-
     1.One dimensional array (1D)
        It represent basically one row or one column of elements .
                e.g=> marks obtained by four students in a subject 50,51,52,53
     2.Two dimensional array (2D)

        It represent a two dimensional matrix that contains m rows & n columns.
                 e.g=> [a,b,c ; 1, 2, 3]
     3.N-dimensional array (ND)
         It can be visualized as an N-dimensional matrix in N-dimensional vector space that is not realizable or
         being seen after N=3.
                  e.g=> [{a,b,c; 1,2,3 ; 4,5,6}; {a,b,c; 1,2,3 ; 4,5,6}; {a,b,c; 1,2,3 ; 4,5,6};{a,b,c; 1,2,3 ; 4,5,6}].

     Creating an array:-
    Creation of an array involves three steps:-
      1. Declaring an array -

type array_name[ ]; or,

type[ ] array_name;

Remember we do not enter the size of the array during declaration.

2. Creating an array

array_name = new type[size] ;

3.putting values into the memory location

array_name[subscript] = value;

                          e.g=> int table [2] [3] = {1,2,3,4,5,6} ;

        Unlike in C, Java protects array from overruns & underruns. Trying to access an array bound its
        boundaries will generate an error message.

** Array length
         Java have an inbuilt function for getting the information about the number elements present in an array.
         We can obtain the length of array "a" using a.length
                           e.g=> int aSize = a.length

**     Strings
         String simply represents the sequence of characters & Java have inbuilt class for strings manipulation & processing called as "String" class.
         The syntax of initializing string is given below:-
                    String string_name ;
                    String_name = new String ("string") ;
             e.g=> String firstName;
                       firstName = new String("Anil") ;

For more information on inbuilt String type & its per-implemented method visit the official site of Java given below
          http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/String.html

**    Vectors
        In this previous tutorial we saw the concept of variable argument method in Java. This feature can also be implemented in Java through the use of "Vector" class contained in "java.util" package.
This class can be used to create generic dynamic array known as vector that can hold objects of any type & any number. The objects do not have to homogeneous.

    Following are the main advantage of vector over array:-

A vector can be used to store even inhomogeneous object that can very in size.
We can add or delete objects from the list as & when required.

** Wrapper class
      Primitive data-types (like char, int, float) may be converted into object type using wrapper classes
      contained in java.lang package.
       e.g=>
      Primitive datatype-->Wrapper Class-->Constructor arguments

boolean--> Boolean--> boolean or String
byte--> Byte--> byte or String
char--> Character--> char
short--> Short--> short or String
int-->Integer--> int or String
long--> Long--> long or String
float-->Float--> float double or String
double-->Double--> double or String

Similarly we can also convert object Numbers to Primitive number using "typeValue( )" method
Method calling Conversion action

int i = IntVal.intValue( ); object to primitive integer
float f = FloatVal.floatvalue( ); object to primitive float
long l = LongValue.longValue( ); object to primitive long
double d = DoubleVal.doubleValue( ); object to primitive double

_______________________________________________________________________
** Take an example program that simply implementted Calender class of java

import java.util.Calendar;
import java.util.Locale;

public class TestFormat {
    
    public static void main(String[] args) {
      long n = 461012;
      System.out.format("%d%n", n);      //  -->  "461012"
      System.out.format("%08d%n", n);    //  -->  "00461012"
      System.out.format("%+8d%n", n);    //  -->  " +461012"
      System.out.format("%,8d%n", n);    // -->  " 461,012"
      System.out.format("%+,8d%n%n", n); //  -->  "+461,012"
      
      double pi = Math.PI;

      System.out.format("%f%n", pi);       // -->  "3.141593"
      System.out.format("%.3f%n", pi);     // -->  "3.142"
      System.out.format("%10.3f%n", pi);   // -->  "     3.142"
      System.out.format("%-10.3f%n", pi);  // -->  "3.142"
      System.out.format(Locale.FRANCE,
                        "%-10.4f%n%n", pi); // -->  "3,1416"

      Calendar c = Calendar.getInstance();
      System.out.format("%tB %te, %tY%n", c, c, c); // -->  "May 29, 2006"

      System.out.format("%tl:%tM %tp%n", c, c, c);  // -->  "2:34 am"

      System.out.format("%tD%n", c);    // -->  "05/29/06"
    }
}

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2012-10-08T04:44:00.002-07:00

Tutorial #9

This tutorial starts with abstract method & classes & will take us through method of putting variable argument

in calling function as well as different types of access specifier present in java with few example on each topic.

So lets starts with -

Abstract Methods & Classes

We have seen in our earlier tutorial that by using final we ensure that the method is not redefined in a subclass.

Java also allow us to do something that is exactly opposite to this, i.e=> We can indicate that a method

must allows be redefined in a subclass, thus making overriding compulsory. This is done using modifier

keyword "abstract" in the method definition.

                      E.g=> abstract class Ball
                                 {
   -------------
   -------------
   abstract void cricket( );
   -------------
   -------------
                                  }

If a class contains more than one abstract method then also it is to be defined in the same way as defined in

the above example.

If we are using abstract class we must have to satisfy the following conditions:-
1. We can-not use abstract classes to instantiate object directly.
2. The abstract methods of an abstract class must be defined in its subclass.
3. We can-not declare abstract constructors or abstract static method.

METHOD WITH VARARGS

Varargs represent variable length arguments in method , which is one of the feature that is being introduced in J2SE 5.0

Varargs syntex -

             <access specifier> <static> void method-name (object . . . arguments)
             {
   -----------normal code (method body)-----------
              }

NOTE- 1.The varargs must be final argument in the argument list of a method

2.Varargs does not generate any compile time error even if an empty argument is passed as a

parameter to a method

Have a look at the example program to understand this concept properly:-

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    // Illustrates the use of varargs to print the string value passed as an argument to a method
class VariableArgs {
    VariableArgs (String... person ){
        for (String name: person){
            System.out.println("Hello"+ name);
        }
    }

    public static void main(String[] args) {
    new VariableArgs("John", "Rupali");

    }
}
//The downloadable link for the above example is given below
https://www.dropbox.com/s/kandq9kw35xbu5s/dyn_dis.java
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   Dynamic method dispatch

It is an important mechanism in Java that is used to implement runtime polymorphism i.e=> In this

mechanism . method overriding is resolved at runtime instead of compile time.

Have a look at an example to understand this concept properly:-

____________________________________________________________________________
class Super {
    public void method(){
        System.out.println("method super");
    }
}

class sub extends Super{
    public void method(){
        System.out.println("Method sub");
    }
}

class dyn_dis{
    public static void main(String args[]){
        Super A= new sub(); //Sub's object refernces assigned Super type references variable
        A.method(); // sub's version of the method will be called

        Super B= new Super();
        B.method(); // super method will be called

        sub C= new sub();
        C.method();    // sub method will be called
    }
}

//The downloadable link for the above example is given below
     https://www.dropbox.com/s/kandq9kw35xbu5s/dyn_dis.java

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Thus in dynamic method dispatch the type of reference variable is irrelevant while choosing a particular

version of the overridden method for invocation;

Instead it solely depends on the type of object being referred by the reference variable.

VISIBILITY CONTROL

It mainly specifies the scope of variable & method's visibility outside the class inside the same package or even outside the package in which class is present.

1. Public Access

Any variable or method that is declared as public is visible to the entire class in which it is declared as well as visible even outside the class.

E.g=> public int number;

public void sum ( ) {...........}

2.Friendly access

It is mainly invoked when non of the access specifier is declared across the variable or method , So it "default access specifier"

The main difference between "public" & "friendly" access is that public modofier makes the field visible every-where regardless of package while friendly makes it visible only in same package.

3. Protected Access

The protected method makes the fields visible not only to all classes & subclasses in the same package

but also to subclasses of other package

4. Private Acess

It enjoys the highest degree of protection where visibilty is only limted to its own class only

E.g=> private int rome;

private int sum( );

5. private protected aceess

This gives the visibility level in between "protected" access & "private" access. This modifier makes the fields visible in all subclasses regardless of package they are in. But they are not accessible by other classes in the same package.

Rule of thumb:-

1.Use "public" if the field is to be visible everywhere.

2.Use "protected" if the field is to be visible everywhere in the crrent package but visible to only

subclasses of other package.

3.Use "default" if the field is to be visible everywhere in the current package only.

4.Use "private protected" if the field is to be visible only in subclasses , regardless of packages.

5. Use "private" if the field is not to be visible anywhere except its own class.

2012-09-28T06:16:00.003-07:00

Tutorial #8

Friends let’s start this tutorial from one of the basic technique that we haven’t discussed

till now , the technique of taking data values from the user to process & writing data to the file

at any drive of our system.

So here it goes

Inputing data from the user or reading & writing in file

import java.io.DataInputStream;

import java.io.FileNotFoundException;

import java.io.FileOutputStream;

import java.io.IOException;

//creating a text file

public class FileInput {

public static void main(String[] args) throws IOException {

//attach a keyboard to data stream

DataInputStream dis = new DataInputStream(System.in);

//attach file to file output stream

FileOutputStream fout = new FileOutputStream("d:\\myfile.txt",true);

//read data from DataInputStream & write into FileOutputStream;

char ch;

System.out.println("enter data with '@' at the end");

while((ch =(char)dis.read())!='@')

fout.write(ch);

fout.close();

}

** Static Member (static method & static variable) in java

The main advantage of static members is that it can be called without instantiating the

corresponding class (i.e=> without creating objects for that class).

The common way of declaring static members (static method & static variable) is given

below-

static int count; //static variable

static int max(int x , it z); //static method

The variable that are declared static is associated with the class itself, so it is changed by

any object also affect its value in other object;

Restriction imposed on static method-

1. They can only call other static method;

2. They can only access static data;

3. They can-not refer to this or super in any way;

E.g=> example explaining the concept of static method & static data properly.

** Nesting of method

A method can be called by its using only its name by another method of the same class.

This is known as nesting of methods.

E.g=> explaning properly about this concept(program 8.5)

** Defining subclass

A subclass is a class that usually inherits (or takes propertoies ) from some other

prebuild class called as parent class (or superclass);

syntax

class subclassname extends superclassname

{

Variable declaration;

Method declaration;

}

The keyword extends signifies that the properties of the superclassname are extended to

the superclassname.

Note:- the constructor in the derived class uses super keyword to pass the value to its

superclass.

E.g=> program showing single inheritance; (program 8.6) beauty

** Features of subclass constructor

Keyword super is used to subject the following condition-

· Super may only be used within a subclass constructor method

· The call to superclass constructor must appear as the first statement within the subclass

constructor.

· The parameter in the super() method for passing parameter to a subclass;

** overriding method

Defining a method in the subclass with same name & argument as being declared in the

superclass is called as method overriding. When that method is called , the method

defined in the subclass is called instead of super class & hence it overrides the

superclass declared method..:)

** Final variable & method

All the methods can be overridden by default in subclass, if we don’t want to allow the

subclass to override the member of the superclass we can declare them using “final”

keyword

E.g=> final int length = 98;

final void pension()

{

----- function body------

}

Final Class

It is the class that can-not be subclassed . This is also being achieved by using the

keyword “final”.

E.g=> final class reaction {------ }

final class action extends reaction {--------}

So from the above example it is clear that a final class can act as subclass but it will

never act as superclass.

** Finalizer method

This concept is just the opposite of initialization. As we know that java has automatic

runtime garbage collector that automatically frees the memory as soon as the program

finishese execution. But object may holds other non-object resources that is being freed

by finalize() method like file descriptor or window system fonts.

                                  This is similar to destructor method in C++;

            Here is the link to download .java file of the example program given in this tutorial
            named as FileInput.java.
   https://www.dropbox.com/s/e6lcl0r5u2zmfsz/FileInput.java

            Just you need to download this file and place it on src of myEclipse & it will get
            ready to run..:)

2012-09-24T09:38:00.000-07:00

Tutorial #7

Hello friends in this tutorial we will mainly see how Classes & objects are being created in

java & ways of creating Method inside the class.

Class & Objects

In common language Class can be considered as user defined data-type of which Objects

are variable.

It can also be considered as the black-box that contains both data & method & we just

need to invoke it with the help of variable without knowing how internally method really does

the work, we are simply interested in its output for a particular sets of inputs.

Syntax:

Class classname {extends superclass}

{

Data item declaration;

Method declaration;

}

Note:- C++ programmer please kept in mind that there is no semicolon after closing brace

as it would have been in C++ class declaration.

** Field (or data) declaration

Data is declared inside the class in the following way-

class Rectangle

{

int length;

int value;

}

Methods declaration

The syntax of declaring method inside the class is shown below-

class

{

Type methodname (parameter- list)

{

Method body;

}

Note- 1. If your method is returning nothing then simply put “void” before method-name in place of type in the above syntax;

2. The parameter list used in the method header should always be declared

independently separated by commas.

E.g=> void getData(int x,w) //invalid

3.Instance variables and methods in the classes are accessible by all the method in the

class but method cannot access variables declared in other class with local scope.

** Creating object

The syntax of creating an instance of the class (or object is given below)-

ClassName ObjectName; //declare the object;

ObjectName =new ClassName(); //instantiating the object

E.g=> house room;

room= new house();

** Constructors

Constructor are the functions whose name is same as the name of the class & mainly

used to initialize the data contained in the class . They also do not specify any return

type, not even void. This is because they return the instance of the class itself.

E.g=> class house

{

int length;

house (int x) //constructor method

{

length =x;

}

Constructor are mainly of two types

1. Default constructor –this type constructor initializes all the objects of a given lass to same

value.

It is also of two types

1.1 System defined- this type of constructor is being class if the user defined default

or parameterized constructor is being called.

1.2 User defined- this type of constructor initializes all the obect defined for a given

class with the same value defined by the used once

2. Parametrerized constructor- This constructor initializes all the objects with different values

as specified while declaring that object.

E.g=> Example of constructors:-

Class peri {

int length, breadth;

//default constructor

peri()

{

length =0;

breadth=0;

}

//parametrized constructor

peri(int x , int y)

{

length=x;

breadth=y;

}

Public static void main (String args[ ])

{

peri a1= new peri();

peri a2 = new peri (5,10)

System.out.println(“the default value of length=”+a1.length);

System.out.println(“the parametrized value of length=”+a2.length);

}

Method overloading

Method overloading is one of the efficient & nice way to create methods with same

name, but different lists & different definitions.

Note that while declaring overloaded function the parameter of each function

have to be different & return type of the method does-not play any part in this.

E.g=> program for function overloading proto-type

Class a1{

float length, breadth;

a1 (float x, float y) //constructor 1

{

length = x;

breadth =y;

}

a1 (float x) //constructor 2

{

length = breadth =x;

}

2012-09-05T03:04:00.001-07:00

Tutorial # 6

The Enhanced for loop

It is also sometime called as “for each loop” which mainly help to go through all the collection
elements efficiently.

Syntax:-

For(Type identifier: Expression)

{

//statements;

}

Where, type represents the data-type or object used & Identifier refers to the name of the
variable & Expression is an instance of java.lang.Iterable interface or simply an array.

E.g=> consider the following statement:

int numarray[3]={56,48,79}

for (int k=0;k<=3;k++)

{

If(numarray[k]>50 && numarray[k]<100])

{

System.out.println(“the selected value is”+numarray[k]);

}

& the above code can be equivalent to the following code-

int numarray[3]={56,48,79}

for (int k:numarray)

{

If(k>50 && k<100)

{

System.out.println(“the selected value is”+k);

}

Jumps in loop

Jump is mainly used to change the continuous flow of execution of the program
according to a given predefined condition.

· Jumping out of the loop

Can be accomplished by using “break” statement. But remember friends, it can only be
used with switch statement & looping statements thats too just to exit from the
immediate single loop in which the programming is currently executing.

· Skipping a part of the loop

Can be mainly accomplished by using “continue” statement, It mainly tells the compiler to skip the following statements & continue with the next iteration.

Labelled loop

In java we can give a label to any block of statements. A label is simply any valid java variable
name.

To give a label to a block simply place it before the block with colon at the end.

E.g=>

loop1: for(……)

{

…………

}

………………

NOTE-

   If we want to jump outside a nested loops or to continue a loop that is outside the current
one, then we simply have to use the labeled break & labeled continue statement respectively.
E.g=>

   //Use of continue & break statement
   class ContinueBreak
   {
public static void main(String args[])
{
   Loop1: for (int i=1;i<100;i++)
{
   System.out.println(" ");
   if(i>=10) break;
   for(int j=1;j<100;j++)
   {
   System.out.println("*");
   if(j==i)
   continue Loop1;
   }
}
                                                                      System.out.println("termination by break");
}
   }

2012-08-26T00:40:00.001-07:00

Java Tutorial #5

Friends today we start our discussion from Decision making processes & concept of looping , where we
will see numerous ways by which we can repeat a process or take decision in java & in the end we will
program few examples in decision making process, looping.

Decision making statements

          if statement
if satement is mainly used to execute a block of code when a given condition inside the if block is correct.
We can also add many conditions inside one if loop by applying && or || logical operator discussed in the
previous tutorial

The basic structure of if block will look somewhat like this:-

               if(test expression)
            {
                 statement block that need to be executed
               }
               statement X;
   The if...else statement

if else statement is mainly used to execute both the aspect of a given expression , if a given expression is correct than, block of if part will gets execute & if the given expression doesn't satisfy the above condition than else part of the block will gets executed

The proper diagramatic explanation of the if...else statement is shown above.

The basic structure of if...else block will look somewhat like this:-

               if(test expression)
         {
                   True block statement
               }
               else
               {
                   False block statement
               }
               Statement X;

The else if ladder

it mainly used to check more than one condition at a time when there is no link between various condition. It
starts checking the condition start from the first if block & if any of the condition matches it executes that
block & gets exited from all the remaining blocks if if or else if statement & if none of the if statement
matches the conditio it simply executes the last else block(if present)

The proper diagramatic explanation of the else if ladder is shown above

The basic structure of else if block will look somewhat like this:-

               if(test expression1)
         {
                   statment-1;
               }
               else if(test expression2)
               {
                   statement-2;
               }
               else if(test expression3)
               {
                   statement-3;
               }
               -----------
               else if(test expressionn)
               {
                   statement-n;
               }
               else
                  default statment; 
                                   
               Statement X;

The switch statement

It is also somewhat like elseif ladder in which if the case of a given expression matches with the listed case then that case's statement blocks gets executed.

NOTE:-Friends keep in mind that if we dont use break statement after each case's block ending the block of the case that satisfy the geiven condition & remaining ll the blocks after that case will also gets executed.

The proper diagramatic explanation of the switch case is shown above

The basic structure of switch statement will look somewhat like this:-

               switch(expression1)
       {
                         case value-1;
                             block-1
                                break;

                         case value-2;
                             block-2
                                break;
                           -------
                           -------
                          default;                                       
                             default-block
                                break;
                         }          
                  Statement X;

Now lets practice one program that can use all the above explained concepts;

    ___________________________________________________________________
  public class DecisionMaking{
 public static void main(String args[])
 {
  int a=325,b=457,c=478;
  System.out.println("largest value among the following is:");
  if(a>b)
  {
   if(a>c)
   {
    System.out.println(a);
   }
   else
    System.out.println(c);
  }
  else{
   if(c>b)
    System.out.println(c);
   else System.out.println(b);
  }
 }
 }
_________________________________________________________________________________

Looping in Java

for loop

This is one of the most used type of looping that mainly used if we know the number of times you need to
execute the loop

The basic structure of the for loop is given below:-

          for(initilization; test condition; increment)
                {
                  body of the loop;
                }
                Statment X;

The while statement

this is also among the famous looping construct that is being mainly used if we dont know the end of the loop or number of times the loop is going to execute

The comparison between for & while loop is shown in below drawn figure;-

The basic structure of the while loop is given below:-

          IntiAlization:
          for(test condition)
                {
                  body of the loop;
                }
                Statment X;

The do-while statement

Till now all the looping conditions we learn use to check condition before executing its block, but
do-while statement allows us to execute its block once before applying the conditions.

It is almost same as use once for seeing genuinity of the product before paying to the shopkeeper

The basic structure of the do-while loop is given below:-

          initilization;
                do
                {
                  body of the loop;
                }
                while(test condition);
                Statment X;

Now lets see an example on looping

Here we are finding the Computing power of 2;

    _________________________________________________________________________
    class Power{
     public static void main(String args[])
        {
         long p;
            int n;
            double q;
            p=1;
            for(n=0;n<10;++n)  
            {
             if (n==0)
                 p=1;
                 else
                  p*=2;
                 q=1.0/(double)p;
                 Syatem.out.println(" "+q+" "+" "+p);
                  
            }
           }
          }

_____________________________________________________________________________

2012-08-21T23:53:00.000-07:00

Java Tutorial #4

Operator and expressions

Arithmetic operator (+,-,*,/,%)

These can operate on any build in numeric data-type of java except on boolean type ('true' , 'false') . All the arithmetic operators work in the same way as they use to do in C or C++

Modulo operator

Modulo operator mainly gives the remainder of two numbers division.
Always keep in mind that sign of the result in modulo arithmetic is always the sign of first operand (or dividend)

e.g=> -14%3=-2
-14%-3=-2
14%-3=2

Unlike C,C++ modulo operator % can be applied to the floating point data as well

The floating point modulus operator returns the floating point equivalent of an integer division.
It simply means that ,the division is carried out with both the floating point operand, but the resulting divisor is treated as integer & resulting in floating remainder will acts as the output of the modulo division of floting point numbers

When arithmetic operation is performed on two different types of data values,the resultant will always be converted into higher precision value

Logical operator

Logical and

can be true only when both the values across && operator should be true

Logical or

can be true only when atleast any one the values across || operator should be true

Logical not

false if expression is anything other than 0

Special operators

Instanceof opertaor

It is an object reference operator and returns "true" if the object on LHS is an instance of the class on the RHS

This opertor mainly help us to determine whether an object belongs to a particular class or not
e.g=> person instanceof student

will be true if person belongs to the class of student otherwise it will return false

Dot operator

is mainly used to access the instance variable & method of class objects

 e.g=>person.age ;                    //refernce to variable age
      person.salary();                //refrence to the method salary

Remember java doesnot have any operator for exponentiaion (or power), in place it have a method function in math class called pow(a,b) that will implement the same work as being done by the operator, if it would have been.(i.e=>a^b or, a to the power b);

y=(int)(a+b)
here the result is being converted into int value

y=(int)a+b
here a is convered into int value & then being added with b , so the resultant may not be an int value.

Generic typecasting
Typecasting is an unsafe operation because the compiler cannot check the wrong typcast. The compiler throws an exception if typecast fails at runtime
When using generics, the compiler insert typecast at appropriate places to implement type casting. So typecast become implicit in palce of explicit. Generics also detremine the typecast error at compile time rather than runtime
syntax

            Class SampleGenerics
            {
             sample code;
            }

e.g=>Illustration of use of generic type in collections
______________________________________________________________________________
______________________________________________________________________________
Following example illustrate how we can print array of different type using a single Generic method:

public class GenericMethodTest
{
   // generic method printArray                         
   public static < E > void printArray( E[] inputArray )
   {
      // Display array elements              
         for ( E element : inputArray ){        
            System.out.printf( "%s ", element );
         }
         System.out.println();
    }

    public static void main( String args[] )
    {
        // Create arrays of Integer, Double and Character
        Integer[] intArray = { 1, 2, 3, 4, 5 };
        Double[] doubleArray = { 1.1, 2.2, 3.3, 4.4 };
        Character[] charArray = { 'H', 'E', 'L', 'L', 'O' };

        System.out.println( "Array integerArray contains:" );
        printArray( intArray  ); // pass an Integer array

        System.out.println( "\nArray doubleArray contains:" );
        printArray( doubleArray ); // pass a Double array

        System.out.println( "\nArray characterArray contains:" );
        printArray( charArray ); // pass a Character array
    } 
}

_______________________________________________________________________________
_______________________________________________________________________________

Selected important math function

Math functions are the part of java.lang Package

atan2(x,y) =>returns an angle whose tangent is x/y (i.e=> it is tan-inverse
function)

exp(x)=>returns e raised to x

rint(x)=>returns truncated value of x

abs(a)=>returns absolute value of a

Syntax
Math.function_name();
eg=>Math.sqrt(x);

2012-08-20T11:40:00.001-07:00

Tutorial 3

Java Tutorial #3

Java Programming Structure
Document section (suggested)
Package statement (optional)
Import statement (optional)
Interface statement (optional)
Class definition (optional)
Package statement (optional)
Main method class { Main method definition }

1.1 Document section- comprises of set of comment lines giving the name of program ,author, & other
details which programmer would like to refer to at later stages

1.2Package statement declares a package name & inform the compiler that the classes defined here
belongs to this package
e.g=> package author

1.3Import statment we can have access to the classes that are not part of our package

1.4Interface statement we can have access to the classes that are not part of our package

1.5Main method is same as in C++ from where the program execurtion starts and end with theend of
main method

Friends,always keep in mind that java is case sensitive ,so int radius & int RAdius are two different
variable (or identifier) not the same one

The character used in java are defined by the unicode charecter set, which is a 16bit character coding
system. So char in java takes 2byte space unlike 1byte space in C or C++

Keywords java language has 50 reserved keywords that are never been used as identifier. all keywords are
given in lower case letter .
For more information about keywords Click here

Secret of java platform Independence

Different language compilers translates source code into machine code for a specific computer. On the
other hand, java compiler produces an inermediary code known as bytecode for a machine called
java-virtual machine, that exists inside the computer memory and simulates computer within computer that
converts bytecode into machine specific code. As bytecode of all the system are same and hence java is
platform independent.

Command line argument

Command line argument is one of the nice way of passing the data at runtime at the time of compilation.
Public static void main(String srgs[])
Here args is declared as an array of strings (known as string object).Any argument provided in command line (at time of execution) are passed to the array args as its element that can be used in the program

Use of Command line argument

 
               /*
         * This program uses command line argument as input
                */
                Class static void main(String args[])
                {
                 int count , i=0;
                    String string;
                    count =args.length ; //inbuilt function to count the

                                                //number of argument passed by the

                                                // user at run time
                    System.out.println("Number of arguments ="+count);
                    while(i < count)
                    {
                     string = args[i];
                        i+=1;
                         System.out.println(i+":"+"Java is"+string+"!");         
                    }
                }

Data-type supported in java

Integer type

java doesnot support the concept of unsigned type,so java integer value are either positive or negative

Floating point

is treated as double precision quantities(double). To force them to be in single precision mode we must
append f or F to the number

NOTEAll mathematical function such as sin,cos,sqrt return or take double type value Floating point data
type support a special value known as Not-a-Number(NaN), that is used to represent the result of
opertation such as divie by zero where actual number is not produced

Character type is same as in C or C++ or any standard procedural or object oriented language

Boolean type is denoted by the keyword boolean and uses only 1 bit of storage that can take only two
values "true" or "false"

NOTEIt should be remembered that wider data type requires more time for manipulation and therefore it is
advisable to use smaller data type whenever possible
one of the great advantage of java is that if a variable is not initialzed it is autometically set to zero(or the
standard default value of that primitive data type)

Typecasting

converts one primitive data-type to another primitive data-type

Automatic conversion

is possible only if the destination type has enough precision to store the source value
eg=> byte b=75;
int a=b; s valid statement

Note that we need to explicitely cast if we are to convert a more precised value to the less precised one

Syntax

type variable1=(type) variable2;

2012-07-28T21:03:00.000-07:00

Tutorial #2

Few important properties of java that needs to be learn &
understand by all java programmers whether he/she is beginner or
professional.so here it goes:-

*java is the first programming language that is independent of hardware for its running & work on any configuration or OS(operating system)

This is mainly because java does-not run on host computer directly,it runs on java virtual machine by converting the program into byte code that are machine independent & that virtual machine converts the byte code according to the configuration requirement type.

*Java does-not use pointers, preprocessor header files,go-to statement & many others .It also eliminate operator overloading that sometime may create chaos in programming.

*Java programs also support functions written in another common languages like C & C++. These functions are called by some special names called as native method.

*java also doesn't include C unique statement keyword sizeof, typedef & also data type like struct & unions .Neither do it has include pre-processor directives like #define,#include,#ifdef.

Instead of this it import statement ,but that use to work much differently than # include as it is attached dynamically at run -time.

*Java also don't have template class as it is present in C++;

Overview of Java

Java in its broad sense has three parts:-

1.J2SE {Core java + Advance java }

(that is mainly same as any other primitive language in its rudimentary form like C & C++

that works as a standalone feature that works on individual computer)

2.J2EE

(this is mainly for application development that helps in developing website & adding amazing

functionality in it )

3.J2ME

(this mainly helps in developing apps & games of mobile phone & has a great rising market now a

days when android apps are becoming so popular)

But for learning any particular branch of java core java of J2SE is very helpful & must in some sense so we start with learning J2SE.

Note that :- *java is pure object oriented language unlike C or C++ (which supports both) . So everything we wrote in java must be inside the class.

*Also unlike C++ class definition in java doesn't ends with semi-colon(;)

* A java application may have any number of classes but only one of them should have main method & program starts from execution of that calls & will end with the execution of that class & if that class links other classes in its body then they intern will also gets executed.

* there are three ways of commenting in java

1. // this will allow commenting for only one line;

2. /* comment */ this will allow commenting for more than one line

3./*comment

*comment continue

Lets end this lecture with developing our first programm:-

//This program simply calculate the square-root of first ten natural numbers :-

__________________________________________________________________________

import java.lang.math;

class SquareRoot

{

public static void main(String args[])

{

double m;

double y;

for(int i=0;i<=10;i++)

{

y=Math.sqrt(i);

System.out.println("The square root of"+i+" = "+y);

}

_______________________________________________________________________________

The best software for programming java is MyEclipse that can be downloaded from the given below site:-

*for 32 bit computer-http://www.filehippo.com/download_eclipse_classic_32/

*for 64 bit computer-http://www.filehippo.com/download_eclipse_classic_64/

And tutorial for writing program in MYEclipse can be sen from the given below sites:-

http://www.vogella.de/articles/Eclipse/article.html#gettingstarted

(remaining we will discus in the next tutorial)

2012-03-15T12:17:00.002-07:00

home
This is our first java tutorial lecture	here we are going to see the history of java & just few basic concepts like variable,& assignment of value to variable in java in various different ways

Java is a programming language originally developed by James Gosling at Sun Microsystems (which has since merged into Oracle Corporation) and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities. Java applications are typically compiled to bytecode (class file) that can run on any Java Virtual Machine (JVM) regardless of computer architecture. Java is a general-purpose, concurrent, class-based, object-oriented language that is specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA), meaning that code that runs on one platform does not need to be recompiled to run on another. Java is currently one of the most popular programming languages in use, particularly for client-server web applications, with a reported 10 million users.

2012-03-15T09:05:00.000-07:00

Java Youth Tutorial & Discussion blog

This blog is mainly introduced for helping students to learn java effectively at one site only, without crawling or moving to several waste-fool sites in the hope of learning some-thing new, or clearing the concept that will become the backbone of your future as a java web-developer or in any emerging field of java.