Java-final keywords

final variable
--------------
A variable whose value cannot be altered/changed is known as final variable.

A variable declared using keyword final is known as final variable

syntax
------
final datatype varname=value;

ex:
final double pi=3.14;

if we want to define constants in a program then we must declare a variable as final.

The only modifier allowed with local variables is final.

we should initliaze a final variable at the time of declaring itself.

final method
------------
A method declared using a keyword final is known as final method

we cannot ovverride final methods in a subclass.


syntax
------
accessmodifier final returntype methodname()
{
//statements
}

ex:
public final void m1()
{

}

Program
--------
class A
{
  public final void m1()
  {
    System.out.println("A");
  }
}
class B extends A
{
  public void m1()
  {
    System.out.println("B");
  }

}

Above code leads to CE because we are overriding final method.

which of the following method definitions are valid?
public final void m1()
public final  abstract void m1()
public final static abstract void m1()
public abstract void m1()
void m1()
public static final void m1()

we cannot declare abstract and final together bcoz it is iilegal combination.abstract method must be overridden whereas final method shoud not be overridden.


final class
-----------
A class declared using keyword final is known final class.

A final class cannot be inherited.

syntax
------
accessmodifier final class ClassName
{
//
}

ex:
final class A
{
  public  void m1()
  {
    System.out.println("A");
  }
}

which of the following declarations are valid?
public final class A{}c
public abstract class A{}c
public final abstract class A{}
public static final class A{}
final class A{}c
abstract class A{}c
public abstract static final class A{}


Reason:A final class cannot be subclassed whereas an abstract class needs subclassing.