title: Declaring an abstract interface in Java may add some additional meaning to that interface?
body: <blockquote>
    <p><strong>Possible Duplicate:</strong><br>
    <a href="https://stackoverflow.com/questions/641536/why-would-one-declare-a-java-interface-method-as-abstract">Why would one declare a Java interface method as abstract?</a>  </p>
  </blockquote>
  
  
  
  <p>The following code snippet defines an <strong>abstract</strong> interface and does the sum of two numbers entered through the console.</p>
  
  <pre><code>package abstractinterface;
  
  import java.util.Scanner;
  
  abstract interface SumInterface
  {
      abstract public void sum();
  }
  
  final class Summation implements SumInterface
  {
      private int x,y;
  
      public Summation(int x, int y)
      {
          this.x=x;
          this.y=y;
      }
  
      public void sum()
      {
          System.out.print("\nSummation = "+(x+y)+"\n\n");
      }
  }
  
  final public class Main
  {
      public static void main(String[] args)
      {
          try
          {
              Scanner s=new Scanner(System.in);
  
              System.out.print("\nEnter a number:-&gt;");
              int x=s.nextInt();
  
              System.out.print("\nEnter another number:-&gt;");
              int y=s.nextInt();
  
              new Summation(x, y).sum();
          }
          catch(NumberFormatException ex)
          {
              System.err.println(ex.getMessage());
          }
      }
  }
  </code></pre>
  
  <hr>
  
  <p>The interface contains one abstract method and it is implemented by the class <strong>Summation</strong>. The only question here is that if the keyword <strong>abstract</strong> is removed from the above interface, does it make some different sense? What is the actual use of such abstract interfaces in Java?</p>