abstract class java constructor
// abstract class
abstract class Shape
{
// abstract method
abstract void sides();
}
class Triangle extends Shape
{
void sides()
{
System.out.println("Triangle shape has three sides.");
}
}
class Pentagon extends Shape
{
void sides()
{
System.out.println("Pentagon shape has five sides.");
}
public static void main(String[] args)
{
Triangle obj1 = new Triangle();
obj1.sides();
Pentagon obj2 = new Pentagon();
obj2.sides();
}
}
Sometimes we may come across a situation where we cannot provide
implementation to all the methods in a class. We want to leave the
implementation to a class that extends it. In such case we declare a class
as abstract.To make a class abstract we use key word abstract.
Any class that contains one or more abstract methods is declared as abstract.
If we don’t declare class as abstract which contains abstract methods we get
compile time error.
1)Abstract classes cannot be instantiated
2)An abstarct classes contains abstract method, concrete methods or both.
3)Any class which extends abstarct class must override all methods of abstract
class
4)An abstarct class can contain either 0 or more abstract method.
// Abstract class
abstract class Animal {
// Abstract method (does not have a body)
public abstract void animalSound();
// Regular method
public void sleep() {
System.out.println("Zzz");
}
}
// Subclass (inherit from Animal)
class Pig extends Animal {
public void animalSound() {
// The body of animalSound() is provided here
System.out.println("The pig says: wee wee");
}
}
class MyMainClass {
public static void main(String[] args) {
Pig myPig = new Pig(); // Create a Pig object
myPig.animalSound();
myPig.sleep();
}
}
/**
* Simple Java program to prove that abstract class can have constructor in Java.
* @author http://java67.blogspot.com
*/
public class AbstractConstructorTest {
public static void main(String args[]) {
Server server = new Tomcat("Apache Tomcat");
server.start();
}
}
abstract class Server{
protected final String name;
public Server(String name){
this.name = name;
}
public abstract boolean start();
}
class Tomcat extends Server{
public Tomcat(String name){
super(name);
}
@Override
public boolean start() {
System.out.println( this.name + " started successfully");
return true;
}
}
Output:
Apache Tomcat started successfully
interface methods{
public void hey();
public void bye();
}
//unable to implement all the abstract methods in the interface so
// the other class automatically becomes abstract
abstract class other implements methods{
public void hey(){
System.out.println("Hey");
}
}
//able to implement all the methods so is not abstract
class scratch implements methods {
public void hey(){
System.out.println("Hey");
}
public void bye() {
System.out.println("Hey");
}
}