How to generate a random number from a probability density function in java?

I have a probability density function,

F(x) = 0 for x < T1

F(x) = (Y/B) for T1 < x < T2

F(x) = 0 for x > T2

How do I generate a random number from this probability density function (for java)? What type of formula should I use for this type of question?