Question

Explain why certain statements don't compile that
mostly related to extends and implements when
used with abstract and final classes.

Interpret two different recusive methods.

Interpret a multi-class program that uses
the main() method's String[] parameter.

Interpret a multi-class program that includes
an interface and uses polymorphism.

Interpret a code snippet that uses a String[][].

Interpret a single-class program that assesses
understanding of the inherited toString() and
equals() methods.

Answer 1

1.Abstract methods compulsory we should override in child classes to provide implementation.

Where as we can't override final methods. Here final, abstract combination is illegal combination for methods.

NOTE :- A final class can not have abstract methods and an abstract class can not be declared final.

2.Recursive Methods:

1.Factorial of a number.

public class Fact {  

    static int factorial(int n){      

          if (n == 1)      

            return 1;      

          else      

            return(n * factorial(n-1));      

    }      

  

public static void main(String[] args) {  

System.out.println("Factorial of 5 is: "+factorial(5));  

}

}

output:

Factorial of 5 is: 120

prints the factorial of 5.

2.Fibonacci Series

public class Fib{  

    static int n1=0,n2=1,n3=0;      

     static void printFibo(int count){      

        if(count>0){      

             n3 = n1 + n2;      

             n1 = n2;      

             n2 = n3;      

             System.out.print(" "+n3);     

             printFibo(count-1);      

         }      

     }        

  

public static void main(String[] args) {  

    int count=15;      

      System.out.print(n1+" "+n2);

      printFibo(count-2);

}  

}

output:

0 1 1 2 3 5 8 13 21 34 55 89 144 233 377

prints the first 15 numbers in Fibonacci series.

3.Interpret string[] in main() method.

we have to take the command line argument.

class cmd
{
  public static void main(String[] args)
  {
    for(int i=0;i< args.length;i++)
    {
    System.out.println(args[i]);
    }
  }
}

output:

Command Prompt F:\〉javac cnd-Java F:\〉java cmd 10 20 20 30 30

4.Multi class program that includes interface and uses polymorphism.

interface Anim
{
public void eat();
}
class Animal implements Anim{
public void eat()
{
System.out.println("animal is eating...");
}
}
class Dog extends Animal{
public void eat(){
System.out.println("dog is eating...");
}
}
class Main extends Dog{
public static void main(String args[]){
Animal a;
a=new Animal();
a.eat();
a=new Dog();
a.eat();
}
}

output:

animal is eating. s eating- - -

5.code that uses string[][].

import java.io.*;

class GFG {

    public static void print2D(int mat[][])

    {

        // Loop through all rows

        for (int i = 0; i < mat.length; i++)

  

            // Loop through all elements of current row

            for (int j = 0; j < mat[i].length; j++)

                System.out.print(mat[i][j] + " ");

    }

  

    public static void main(String args[]) throws IOException

    {

        int mat[][] = { { 1, 2, 3, 4 },

                        { 5, 6, 7, 8 },

                        { 9, 10, 11, 12 } };

        print2D(mat);

    }

}

output:

1 2 3 4 5 6 7 8 9 10 11 12

prints all elements in the two dimensional matrix.

6.

Interpret a single-class program that assesses understanding of the inherited toString() and
equals() methods

code:

class Main
{
//the class defining a circle
int radius;
public Main(int i)
{
radius = i;
}

//Overriding toString() method

@Override
public String toString()
{
return "Area = "+(3.14*radius*radius);
}
//if both have same radius
public void equals(Main b)
{
if(this.radius==b.radius)
System.out.print("Both circles are equal.");
else
System.out.print("Circles are not");
}
  
public static void main(String[] args)
{
Main a = new Main(10); // Creating an instance of A
Main b=new Main(10);
System.out.println(a);
a.equals(b);
}
}

output:

Area314.0 Both circles are equal.

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