Best Java Programming training in Nagpur

1
CORE JAVA

• PSK TECHNOLOGIES
• An ISO 90012015 (QMS) Certified IT Company
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• website www.pskitservices.com

2

• CONTENT
• Constructor
• Static variable
• This Keywords
• Inheritance
• Abstraction Interface

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3

• Constructor
• A constructor is a special member function
  whose task is to initialize the objects of its
  class. It is special because its name is the same
  as the class name. The constructor is invoked
  whenever an object of its associated class is
  created. It is called constructor because it
  construct the values of data member of the class.

A constructor is declared and defined as
follows //class with a constructor Class
integer int m,n Public integer (void)
//constructor declared . . Integer
integer (void) //constructor defined m 0 n
0
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• When a class contains a constructor like the one
  defined above, it is guaranteed that an object
  created by the class will be initialized
  automatically. For example, the declaration
  Integer int1 // object int1 created.
• Not only created the object int1 of the integer
  but also initializes its data members m and n to
  zero. There is no need to write any statement to
  invoke.
• the constructor function (as we do with the
  normal member function). If a normal member
  function is defined for zero initialization, we
  would need to invoke this function for each of
  the objects separately. This would be very
  inconvenient, if there are a larger number of
  objects.
• A constructor that accepts no parameters is
  called the default constructor. The default
  constructor for class A is AA (). If no such
  constructor is defined, then the compiler
  supplies a default constructor.

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• Program
• class Student4
• int id
• String name Student4(int i,String n)
• id i name n
• void display()
• System.out.println("Id"id"\t""Name"name)
• public static void main(String args)
• Student4 s1 new Student4(111,"Karan")
• Student4 s2 new Student4(222,"Aryan")
• s1.display()

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• Program
• Constructor overloading
• class Student5
• int id
• String name int age
• Student5(int i,String n)
• id i name n
• Student5(int i,String n,int a)
• id i name n agea
• void display()
• System.out.println(id" "name" "age)

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7

• Copy Constructor
• Java Copy Constructor
• There is no copy constructor in java. But, we can
  copy the values of one object to another like
  copy constructor in C.
• There are many ways to copy the values of one
  object into another in java. They are
• By constructor
• By assigning the values of one object into
  another
• By clone() method of Object class/

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• Program
• class Student6
• int id
• String name Student6(int i,String n)
• id i name n
• Student6(Student6 s)
• id s.id
• name s.name
• void display()
• System.out.println(id" "name)

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• STATIC VARIABLE
• Static Member Function
• 1) Like static member variable we can also have
  static member function.
• 2) A static function can have access to only
  other static member (function or variable)
  declared in same class.
• 3) A static member function can be called using
  the class name. class_name function_name
• When counter () function is called and gets
  destroyed each time when counter () function
  ends.But, if we makes it static, once
  initialized count will have a scope till the end
  of main () function and it will carry, its
  value through function calls too. If you dont
  initialized a static variable, they are by
  default initialized to zero.

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• Program
• class Counter2
• static int count //will get memory only once and
  retain its value
• Counter2()
• count
• System.out.println(count)
• /void display()
• System.out.println("\n\n\n"count)
• /
• public static void main(String args)

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• Why Java Main Method Is Static?
• Because object is not required to call static
  method if it were non-static method,
• jvm create object first then call main() method
  that will lead the problem of extra memory
  allocation.

• Java static block
• Is used to initialize the static data member.
• 2) It is executed before main method at the time
  of class loading
• class A2
• static
• System.out.println("static block is invoked")
• public static void main(String args)
• System.out.println("Hello main")

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• THIS KEYWORD
• Definition of This
• To refer the current class instance variable to
  invoke the current class constructor to invoke
  the current class method to pass as an argument
  in the method call to pass as an argument in the
  constructor call to return the current class
  instance proving this keyword there can be a lot
  of usage of java this keyword. In java, this is a
  reference variable that refers to the current
  object.
• Using this keyword
• Here is given the 6 usage of java this keyword.
• 1.this keyword can be used to refer current class
  instance variable.
• 2.this() can be used to invoke current class
  constructor.
• 3.this keyword can be used to invoke current
  class method (implicitly)
• 4.this can be passed as an argument in the method
  call.
• 5.this can be passed as argument in the
  constructor call.
• 6.this keyword can also be used to return the
  current class instance

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• Program
• class This1
• int id
• String name
• This1(int id,String name)
• this.id id
• this.name name
• void display()
• System.out.println(id" "name)
• public static void main(String args)
• This1 s1 new This1(11,"Karan")

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• Constructor Call Using This
• This() can be used to invoked current class
  constructor.
• The this() constructor call can be used to invoke
  the current class constructor (constructor
  chaining).
• This approach is better if you have many
  constructors in the class and want to reuse that
  constructor.

• Program
• class ThisCon
• int id
• String name
• ThisCon()
• System.out.println("default constructor
• is invoked")
• ThisCon(int id,String name)
• this ()
• //it is used to invoked current class
  constructor.
• this.id id
• this.name name
• void display()

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• Program
• This keyword refers to the current class instance
  variable.
• In this program, we are printing the reference
  variable and this, output of both variables are
  same
• class A5
• void m()
• System.out.println(this)//prints same reference
  ID
• public static void main(String args)
• A5 objnew A5()
• //System.out.println(obj)
• //prints the reference ID obj.
• m()

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• Inheritance
• Why multiple inheritance is not in java.
• Program
• class A
• A()
• System.out.println("A constructor called")
• System.out.println("asd")
• class B extends A
• B()
• System.out.println("B constructor called")

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• Program
• class A
• int a,b
• void getA(int x,int y)
• ax by
• System.out.println("Super Add"(ab))
• class B extends A
• int m,n
• void getB(int t,int s,int p,int q)
• super.getA(t,s) mp
• nq

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18

• Abstraction Interface
• Abstract class in Java
• A class that is declared with abstract keyword,
  is known as abstract class in java. It can have
  abstract and non-abstract methods (method with
  body).Before learning java abstract class, let's
  understand the abstraction in java first.
• Abstraction in Java
• Abstraction is a process of hiding the
  implementation details and showing only
  functionality to the user. Another way, it shows
  only important things to the user and hides the
  internal details for example sending sms, you
  just type the text and send the message. You
  don't know the internal processing about the
  message delivery. Abstraction lets you focus on
  what the object does instead of how it does it.
• Ways to achieve Abstraction
• There are two ways to achieve abstraction in java
  
• Abstract class (0 to 100)
• Interface (100)

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19

• Program
• abstract class Bank
• abstract int getRateOfInterest()
• class SBI extends Bank
• int getRateOfInterest()
• return 7
• class PNB extends Bank
• int getRateOfInterest()
• return 9

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20

• Interface With Class
• An interface in java is a blueprint of a class.It
  has static constants and abstract methods only.
  The interface in java is a mechanism to achieve
  fully abstraction. There can be only abstract
  methods in the java interface not method body.
  It is used to achieve fully
  abstraction and multiple inheritance in Java.

• Program
• interface f1
• public void get(int x,int y)
• interface f2
• public void show()
• class Myclass implements f1,f2
• int a,b
• public void get(int x,int y)
• ax by
• public void show()

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• Program
• import java.util.
• interface f1
• public void get()
• final int c5
• interface f2
• public void show()
• class Myclass implements f1,f2
• int a,b
• Scanner scnew Scanner(System.in)
• public void get()
• System.out.println("Enter a and b")

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