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Use of final in Inheritance in java

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Using final to Prevent Overriding

While method overriding is one of Java’s most powerful features, there will be times when you will want to prevent it from occurring. To disallow a method from being overridden, specify final as a modifier at the start of its declaration. Methods declared as final cannot be overridden. The following fragment illustrates final:

/* JAVA program to understand to use of final in Inheritance  */
/* www.codewindow.in */
class A 
{
    final void meth()
    {
        System.out.println("This is a final method.");
        
    }
}
class B extends A
{
    void meth()
    { // ERROR! Can't override.
        System.out.println("Illegal!");
        
    }
}

Because meth( ) is declared as final, it cannot be overridden in B. If you attempt to do so, a compile-time error will result.

Using final to Prevent Inheritance

Sometimes you will want to prevent a class from being inherited. To do this, precede the class declaration with final. Declaring a class as final implicitly declares all of its methods as final, too.

Here is an example of a final class:

/* JAVA program to understand to using final to Prevent Inheritance  */
/* www.codewindow.in */
final class A 
{
// ...
}
// The following class is illegal.
class B extends A
{ // ERROR! Can't subclass A
// ...
}

it is illegal for B to inherit A since A is declared as final.