Converting ecliptical to equatorial coordinates
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This is a standard problem with using an arctan function (inverse tan function returns a value between -90 and +90). A lot of programming languages have two functions the simple one like you appear to have used and a more complex one that takes two parameters for when you are dividing (before the arctan function) as in this case. (This is described in further detail at (http://youtu.be/_JbkTK17MrY)

In Java you can use α=atan2((cos ε∗sin λ−sin ε∗tan β), cos λ) you may need to add 360 if the angle returned is negative.

An alternative is α=atan2(cosβsinλcosε−sinβsinε,cosβcosλ). This is equivalent in most cases but avoids an infinite term tanβtan⁡β at the ecliptic poles, costing one more trig function call.