Chapter 4, Problem 60E

Challenge exercise Implement a method in StockManager to print details of all products with stock levels below a given value (passed as a parameter to the method).

Modify the addProduct method so that a new product cannot be added to the product list with the same ID as an existing one.

Add to StockManager a method that finds a product from its name rather than its ID:

public Product findProduct (String name)

In order to do this, you need to know that two String objects, s1 and s2, can be tested for equality with the boolean expression

S1. equals (s2)

More details about comparing Strings can be found in Chapter 6.