strange alternating array

Well hello java enjoyers, i am new to java but not programing all together. I know some python and c+ but not much else. I was trying to figure out away to write a program that reads a sequence of integers into an array list and computes the some of the numbers. But the computation must alternate in between + and -. For example
Number set [4,2,5,7,6,7]
computation 4+2-5+7-6+7=9
output 9
im snaning in the number set and trying to use a for loop but cant figure it out. Any suggestions?