Multilevel Inheritance

 

class Animal {

void eat() {

System.out.println("An Animal is Created");

System.out.println("Animal eats");

}

}

class Dog extends Animal {

void sound() {

System.out.println("A dog is created");

System.out.println("A dog barks");

}

}

class BullDog extends Dog {

void height() {

System.out.println("A BullDog is created");

System.out.println("A BullDog has small Height");

}

}

public class TestMultiLevelInheritance {

public static void main(String args[]) {

BullDog bd = new BullDog();

bd.eat();

bd.sound();

bd.height();

}

}

Single level Inheritence

 

class Animal {

void eat() {

System.out.println("An Animal is Created");

System.out.println("Animal eats");

}

}

class Dog extends Animal {

void sound() {

System.out.println("A dog is created");

System.out.println("A dog barks");

}

}

public class TestSingleInheritance {

public static void main(String args[]) {

// eat method was not defined in Dog class

// so it was inherited from Animal class

// This is single level inheritance

Dog dog = new Dog();

dog.eat();

dog.sound();

}

}

Real time Use of "This" Keyword

 

class StudentData4{

    int rollNo;

String name;

String course;

float fee;

//constructor to assign value;

StudentData4(int rollNo, String name,String course){

this.rollNo = rollNo;

this.name = name;

this.course = course;

}

StudentData4(int rollNo, String name,String course,float fee){

//this will reuse the upper constructor i.e having three parameters

//this statement should be first statement of constructor

this(rollNo,name,course);

this.fee = fee;

}

void display(){

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("course of Student is :" + course);

System.out.println("Fee of student is :" + fee);

}

}

public class RealUseOfThis{

public static void main(String args[]){

StudentData4 s1 = new StudentData4(123,"Kalam","LLB");

StudentData4 s2 = new StudentData4(345,"Kejriwal","B.TECH",75000);

System.out.println("---------------------------------------------------");

System.out.println("Details of First Student");

s1.display();//calling display method

System.out.println("---------------------------------------------------");

System.out.println("Details of Second Student");

s2.display();//calling display method

System.out.println("---------------------------------------------------");

}

}

Using THIS keyword

 class StudentData3{

int rollNo;

String name;

static String college = "VCE";

//constructor to assign value;

StudentData3(int rollNo, String name){

this.rollNo = rollNo;

this.name = name;

}

void display(){

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("Collge of student is :" + college);

}

}

public class TestStudent3{

public static void main(String args[]){

StudentData3 s1 = new StudentData3(123,"Niharika");

StudentData3 s2 = new StudentData3(345,"Kayna");

System.out.println("---------------------------------------------------");

System.out.println("Details of First Student");

s1.display();//calling display method

System.out.println("---------------------------------------------------");

System.out.println("Details of Second Student");

s2.display();//calling display method

System.out.println("---------------------------------------------------");

}

}

Printing data of an class object without THIS keyword

class StudentData2{

int rollNo;

String name;

static String college = "VCE";

//constructor to assign value;

StudentData2(int rollNo, String Name){

//As both variables (local and instance) are same

// zero and null value will be printed;

rollNo = rollNo;

name = name;

}

void display(){

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("Collge of student is :" + college);

}

}

public class TestStudent2{

public static void main(String args[]){

StudentData2 s1 = new StudentData2(123,"Niharika");

StudentData2 s2 = new StudentData2(345,"Kayna");

System.out.println("---------------------------------------------------");

System.out.println("Details of First Student");

s1.display();//calling display method

System.out.println("---------------------------------------------------");

System.out.println("Details of Second Student");

s2.display();//calling display method

System.out.println("---------------------------------------------------");

}

}

Using Static method

 

class StudentData1{

int rollNo;

String name;

static String college = "VCE";

//static method to change the value of college

static void alter(){

college = "MDU"; //changing value of static varible

college = "BBPS";

}

//constructor to assign value;

StudentData1(int r, String s){

rollNo = r;

name = s;

}

void display(){

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("Collge of student is :" + college);

}

}

public class TestStudent1{

public static void main(String args[]){

StudentData1 s1 = new StudentData1(123,"Niharika");

StudentData1 s2 = new StudentData1(345,"Kayna");

StudentData1.alter(); //Calling static method alter();

System.out.println("------------------------------------------------");

System.out.println("Details of First Student");

s1.display();//calling display method

System.out.println("------------------------------------------------");

System.out.println("Details of Second Student");

s2.display();//calling display method

System.out.println("------------------------------------------------");

}

}

Use of Static Variable with Class and Object

 class StudentData{

    int rollNo;

String name;

static String college = "VCE";

StudentData(int r, String s){

rollNo = r;

name = s;

}

void display(){

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("Collge of student is :" + college);

}

}

public class TestStudent{

public static void main(String args[]){

StudentData s1 = new StudentData(123,"Niharika");

StudentData s2 = new StudentData(345,"Kayna");

System.out.println("---------------------------------------------------");

System.out.println("Details of First Student");

s1.display();

System.out.println("---------------------------------------------------");

System.out.println("Details of Second Student");

s2.display();

System.out.println("---------------------------------------------------");

}

}

Copying data of a object to another object without using Copy constructor

 public class Pupil1 {

int rollNo;

String name;

int age;

Pupil1(int r, String s, int a) {

rollNo = r;

name = s;

age = a;

}

Pupil1(){}

void display() {

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("Age of student is :" + age);

}

public static void main(String args[]) {

Pupil1 p1 = new Pupil1(123, "Sudeep", 25);

Pupil1 p2 = new Pupil1();

p2.rollNo = p1.rollNo;

p2.name = p1.name;

p2.age = p1.age;

System.out.println("---------------------------------------------------");

System.out.println("Details of First Student");

p1.display();

System.out.println("---------------------------------------------------");

System.out.println("Details of Second Student copied from first Student");

System.out.println()

p2.display();

System.out.println("---------------------------------------------------");

}

}

Copy Constructor

 

public class Pupil {

int rollNo;

String name;

int age;

Pupil(int r, String s, int a) {

rollNo = r;

name = s;

age = a;

}

Pupil(Pupil p) {

rollNo = p.rollNo;

name = p.name;

age = p.age;

}

void display() {

System.out.println("Roll no of student is :" + rollNo);

System.out.println("Name of student is :" + name);

System.out.println("Age of student is :" + age);

}

public static void main(String args[]) {

Pupil p1 = new Pupil(123, "Sudeep", 25);

Pupil p2 = new Pupil(p1);

System.out.println("---------------------------------------------------");

System.out.println("Details of First Student");

p1.display();

System.out.println("---------------------------------------------------");

System.out.println("Details of Second Student copied from first Student");

p2.display();

System.out.println("---------------------------------------------------");

}

}

Constructor Overloading

 class Worker5 {

    int id;

String name;

int age;

//Constructor with two arguments

Worker5(int i, String n) {

System.out.println("Constructor with two parameter was invoked");

id = i;

name = n;

}

//constructor with three arguments

Worker5(int i, String n, int a) {

System.out.println("Constructor with three parameter was invoked");

id = i;

name = n;

age = a;

}

void display() {

System.out.println("Id of worker is :" + id);

System.out.println("Name of worker is :" + name);

System.out.println("Age of worker is :" + age);

}

public static void main(String args[]) {

Worker5 w1 = new Worker5(123, "John");

Worker5 w2 = new Worker5(198, "Mohmad", 25);

w1.display(); //age will be zero i.e default value

w2.display();

}

}