Answer:

The sum of integers 1 to 100 is Triangle(100)

Actually, you would probably use the familiar formula 1+2+3+ ... +n = (n*(n+1))/2.

Complete Program

class SumOfIntegers
{
  public static int sum( int first, int last )
  {
    if ( first==last )
      return last;
    else
      return first + sum ( first+1, last );
  }
  
  public static void main ( String[] args )
  {
    int start = Integer.parseInt( args[0] );
    int end   = Integer.parseInt( args[1] );
    System.out.println( "Sum from " + start + " to " + end + " is: " +
      sum( start, end ) );   
  }
  
}

Here is a complete program you may want to play with.

The program expects start and end to come from the command line. (See Chapter 65.) Here is an example run:

C:\JavaCode>java SumOfIntegers 50 100
Sum from 50 to 100 is: 3825

In this program, both methods are static, so you don't need to create an object to invoke sum().

QUESTION 12:

Would the following method compute the same thing?

public static int sum( int first, int last )
{
  return Triangle( last ) - Triangle( first-1 );
}