Problem #$4(8$ marks$)$

A formula that computes the sum of the first $n$ integers is $1+2+3+$dots$+n.$ The recursive formula can

be expressed as:

$1+2+3+$dots$+n=n+(1+2+3+$dots$+(n-1))$

Write a static method that implements this recursive formula to compute the sum of the first $n$ integers.

Place the method in a test program $($Recursive$\_$Sum$\_$Test.java$)$ that allows the user to enter the values

of $n$ until the sentinel value $-999$ is entered. Your method should not use a loop to add the first $n$

integers.use java