abstract class program in java code example
Example 1: abstract class in java
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.
Example 2: What are abstract methods in java
An abstract method is the method which does’nt have any body.
Abstract method is declared with
keyword abstract and semicolon in place of method body.
public abstract void ();
Ex : public abstract void getDetails();
It is the responsibility of subclass to provide implementation to
abstract method defined in abstract class
Example 3: abstract class java constructor
/**
* 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