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
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