ArrayList FRQ: ItemInventory

ArrayList FRQ: ItemInventory

The ItemInfo class stores information about an item at a store. A partial declaration is shown.

public class ItemInfo
{
    /** Returns the name of the item */
    public String getName()
    { /* implementation not shown */ }

    /** Returns a value greater than 0.0 that represents the cost of a single unit of the item,
     * in dollars */
    public double getCost()
    { /* implementation not shown */ }

    /** Returns true if the item is currently available and returns false otherwise */
    public boolean isAvailable()
    { /* implementation not shown */ }

    /* There may be instance variables, constructors, and methods that are not shown. */
}

The ItemInventory class maintains an ArrayList named inventory that contains all items at the store. A partial declaration is shown.

public class ItemInventory
{
    /** The list of all items at the store */
    private ArrayList<ItemInfo> inventory;

    /**
     * Returns the average cost of the available items whose cost is between
     * lower and upper, inclusive
     * Precondition: lower <= upper
     *               At least one available element of inventory has a cost
     *               between lower and upper, inclusive.
     *               No elements of inventory are null.
     */
    public double averageWithinRange(double lower, double upper)
    { /* to be implemented */ }

    /* There may be instance variables, constructors, and methods that are not shown. */
}

Write the ItemInventory method averageWithinRange. The method should return the average cost of the available items in inventory whose cost is between the parameters lower and upper, inclusive.

Suppose inventory contains the following seven ItemInfo objects.

Name	action figure	hair brush	frying pan	dish sponge	coffee mug	scarf	watch
Cost	20.0	7.99	45.0	2.0	10.0	59.0	45.0
Is Available	true	true	true	false	true	true	false

For the inventory shown, averageWithinRange(10.0, 50.0) should return 25.0, which is equal to the average cost of the available items within the specified range (a $20 action figure, a $45 frying pan, and a $10 coffee mug). Although the watch is within the specified range, it is not available.

Complete method averageWithinRange.