Skip to main content

Abstract class-1

Abstract class:-abstract is a  modifier used for class and methods, abstract modifier is used for class than that class must be inherit by other class otherwise that class will be useless and nobody can create object of abstract class directly but we can create object of sub class of abstract class. Abstract modifier is used on methods, those methods called abstract methods. An abstract method shows only requirement specification only and implementation provided by sub class of abstract class, if sub class not provides implementation of abstract methods than that sub class must be declared as an abstract.
Abstract class can contains both concrete methods as well as abstract methods. But normal class or non abstract class cannot contain abstract methods.
If any class is declared as an abstract than that class not compulsorily contains abstract methods but if any class contains abstract methods that class must be declared with abstract modifier.

1)   Abstract class may be empty.
2)   Abstract class can contain concrete methods only.
3)   Abstract class can contain abstract methods only.
4)   Abstract class can contain concrete methods and abstract methods.


Example1:-Student.java


 class Student
{
abstract void disp();
}

Output:-

C:\JAVATECH>javac Student.java
Student.java:1: error: Student is not abstract and does not override abstract method disp() in Student
class Student
^
1 error

Example2:-Student.java

class Student
{
void disp();
}

Output:-

C:\JAVATECH>javac Student.java
Student.java:3: error: missing method body, or declare abstract
 void disp();
      ^
1 error

Example3:-

abstract class Student
{
abstract void disp();
public static void main(String[]args)
{
System.out.println("Well-Come Friends");
}
}

Output:-

C:\JAVATECH>javac Student.java
C:\JAVATECH>java Student
Well-Come Friends

Example4:-

abstract class Student
{
abstract void disp();
public static void main(String[]args)
{
Student s=new Student();
System.out.println("Well-Come Friends");
}
}

Output:-

C:\JAVATECH>javac Student.java
Student.java:6: error: Student is abstract; cannot be instantiated
Student s=new Student();
          ^
1 error

Example5:-Test.java

abstract class Student
{
abstract void disp();
}
class Test extends Student
{
public static void main(String[]args)
{
Test t=new Test();
System.out.println("Well-Come Friends");
}
}

Output:-

C:\JAVATECH>javac Test.java
Test.java:5: error: Test is not abstract and does not override abstract method disp() in Student
 class Test extends Student
 ^
1 error

Example6:- 

abstract class Student
{
abstract void disp();
}
abstract class Test extends Student
{
public static void main(String[]args)
{
Test t=new Test();
System.out.println("Well-Come Friends");
}
}

Output:-

C:\JAVATECH>javac Test.java
Test.java:9: error: Test is abstract; cannot be instantiated
Test t=new Test();
       ^

1 error
Labels:

Comments

Post a Comment

Popular posts from this blog

inheritance

INHERITANCE:- Inheritance is the process of code re-usability, using this property software or applications can develop in less time or can develop rapidly. Inheritance increases the readability of code and decrease redundancy or repetition of code or reduces size of code. Use of previously developed code in future any number of times is called inheritance. Through inheritance variables and methods of class can inherited. Types of Inheritance:- 1)         Single or Single level inheritance 2)         Multilevel inheritance 3)         Hierarchical inheritance Java does not support to multiple inheritance. Single or single level inheritance:- In a single inheritance a class is inherited by a single class. In a single or single level inheritance a sub class having only one super class directly or indirectly. Syntax: -        class Subclass ex...
Post a Comment
Read more

Inheritance-4

Example10:- class Student { Student() { System.out.println("This is super class Zero argument constructor"); } Student(String s) { System.out.println("This is super class One argument constructor"); } } class Test extends Student { Test() { super(null); System.out.println("This is sub class Zero argument constructor"); } public static void main(String[]args) { Test t=new Test(); } } Output:- C:\JAVATECH>javac Test.java C:\JAVATECH>java Test This is super class One argument constructor This is sub class Zero argument constructor Example11:- class Student { Student() { System.out.println("This is super class Zero argument constructor"); } Student(String s) { System.out.println("This is super class One argument constructor"); } } class Test extends Student { Test() { super(); super(null); System.out.println("This is su...
Post a Comment
Read more

Abstraction,Encapsulation And Inheritance

Abstraction  is a one of the great feature of Oops,in this feature hide entire details of product, show only requirement specifications(what product will do). The main purpose behind abstraction is to increase productivity or use of product without knowledge of product implementation. in this case the person don't know how product  was implemented but know how product works or action of product. In java abstraction is achieved by abstract class and interface,here interface provide 100% abstraction and abstract class provide partial abstraction. For example: - ATM machine is example of abstraction.  every technical and non-technical person use facility of ATM without knowing the entire process. they know if they click on withdraw button then they can withdraw money from ATM machine but they don't know when they click on withdraw button the request is send to the server and after go into database and so on. Here ATM machine show only requirement specificat...
Post a Comment
Read more