A sealed expression tree in Java
Java interview exercise on Records, classes & interfaces, difficulty 2 of 3. Solve it in the editor beside a worked example; the tests run the moment you do.
Write sealed interface Expr permits Num, Add, Mul with records Num(int value), Add(Expr left, Expr right) and Mul(Expr left, Expr right), and eval(expr) that computes the value with a switch over the sealed type (recursive for Add and Mul).
Each exercise pairs a worked example with a twin problem to solve in a real editor; the tests run the moment you do. Progress is saved in your browser, and in your account if you sign in.