oops.

class and object

package program;

class demo{

int age=22;

String name="ved varshney";

void show(){

    System.out.println("age is : "+age +" name is : "+name);

}

}

public class code{

public static void main(String[] args) {

demo r = new demo();

r.show();

}

}  

constructor - 

Constructor is a special method which name is same as class name . The main purpose of

constructor is to initialize the objects.

every java class has constructor.

A constructor is automatically called at the time of object creation.

A constructor never contain any return type including void.

Types- 1 copy

2 default

3 parameterized

4 private

parameterized constructor  - 

class demo{ int age; String name; demo(int a , String s){ age=a; name=s; System.out.println("age is : "+age +"\nname is : "+name); } } public class Main{ public static void main(String[] args) { demo r = new demo(22,"ved"); } }  

Default constructor - 

class demo{ int a; String s; // demo(){ // } void show(){ System.out.println(a+" "+s); } } public class Main { public static void main(String[] args) { demo d = new demo(); d.show(); } }  

No argument constructor ->

class A{ int a; String s; // no argument constructor A(){ a=10; s="ved"; } void show(){ System.out.println(a+" "+s); } } public class Main { public static void main(String[] args) { A r = new A(); r.show(); } }

copy constructor - 

package program;

import java.util.*;

class demo{

int a , b;

demo(int a , int b){

this.a=a;

this.b=b;

System.out.println(a+" "+b);

}

demo(demo ref){

a=ref.a;

b=ref.b;

System.out.println(a+" "+b);

}

}

public class code {

    public static void main(String[] args) {

    demo d1 = new demo(10,20);

    demo d2 = new demo(d1);

}

}

private constructor - 

package program;

import java.util.*;

public class code {

int a;

String s;

private code(){

System.out.println(a+" "+s);

}

    public static void main(String[] args) {

    code d1 = new code();

}

}

constructor overloading - 

// Constructor overloading program

package program;

import java.util.*;

public class code {

int a;

String s;

// private constructor

private code(){

System.out.println(a+" "+s);

}

// Parameterized constructor

code(int a , String s){

    this.a=a;

    this.s=s;

    System.out.println(a+" "+s);

}

// Copy constructor

code(code ref){

    a=ref.a;

    s=ref.s;

    System.out.println(a+" "+s);

}

    public static void main(String[] args) {

    code d1 = new code();

    code d2 = new code(10,"ved");

    code d3 = new code(d2);

}

}

simple inheritance -

package program;

// import java.util.*;

class student{

    int roll;

    int marks;

    String name;

    protected void intput(){

        System.out.println("enter details= ");

    }

}

public class code extends student {

void disp(){

    roll=1;

    marks=98;

    name="ved";

    System.out.println(roll+" "+marks+" "+name);

}

public static void main(String[] args) {

code c = new code();

c.intput();

c.disp();

}

}  

Multi-Level inheritance-

package program;

// import java.util.*;

class A{

    int a ,b,c;

    void add(){

       a=10;

       b=5;

       c=a+b;

       System.out.println("add = "+c);

    }

    void sub(){

       a=10;

       b=5;

       c=a-b;

       System.out.println("sub = "+c);

    }

}

class B extends A{

void mul(){

       a=10;

       b=5;

       c=a*b;

       System.out.println("mul = "+c);

}

void div(){

       a=10;

       b=5;

       c=a/b;

       System.out.println("div = "+c);

}

}

public class code extends B{

void rim(){

       a=10;

       b=5;

       c=a%b;

       System.out.println("rim = "+c);

}

public static void main(String[] args) {

code c = new code();

c.add();

c.sub();

c.mul();

c.div();

c.rim();

}

}  

Hierarchy Inheritance-

rivpackage program;

// import java.util.*;

class A{

    void sup(){

       System.out.println("super class");

    }

}

class B extends A{

void sub1(){

       System.out.println("sub class 1");

}

}

class C extends A{

void sub2(){

       System.out.println("sub class 2");

}

}

public class code{

public static void main(String[] args) {

B obj1 = new B();

obj1.sup();

obj1.sub1();

System.out.println();

C obj2 = new C();

obj2.sup();

obj2.sub2();

}

}

Method Overloading-

package program;

// import java.util.*;

class A{

void add(){

    int a=10,b=5,c;

    c=a+b;

    System.out.println(c);

}

void add(int a , int b , int c){

    int d;

    d=a+b+c;

    System.out.println(d);

}

}

public class code{

public static void main(String[] args) {

A r = new A();

r.add();

r.add(1,2,3);

}

}  

Method Overriding-

class A{ void show(){ System.out.println("super classs"); } } class B extends A{ @Override void show(){ super.show(); System.out.println("sub class"); } } public class Main { public static void main(String[] args) { A obj = new B(); obj.show(); } }

Encapulation-

class A {

      

     private int value;

     

     public void setValue(int value){

     this.value=value;

     }

     

     public int getValue(){

           return value;

     }

}

public class Main

{

public static void main(String[] args) {

     A obj = new A();

     obj.setValue(50);

     System.out.println(obj.getValue());

}

}