Players must be at least 19 years old at some point during the year of the draft. If the player's 19th birthday will be the next year, they are too young. If a player is from the United States, it must be at least one year after the graduation of his high school class. Some players who are star players go to college and play college basketball for just one year (because they cannot enter the draft right out of high school), then enter the NBA draft. These players are called "one and dones". Other players enter the draft after two or three years in college, and other players are drafted after playing in college for all four years that they can.