Java programinig

Use the recursion to solve the following problems$1.$ Calculate the sum of an array of n integers.

$2.$ Compute Powers, p$($x$,$n$)=$xn

$3.$ Revers an Array of n integers

$4.$ Calculate the length of string $($number of characters$)$

$5.$ Implement the tail recursion for problems $1$ and $2.$