Gizmo
"Gizmo" is a problem from the College Board's AP Computer Science A course description. Let's take a look at it.
The Gizmo class represents gadgets that people purchase. Some Gizmo objects are electronic and others are not. A partial definition of the Gizmo class is shown below.
public class Gizmo
{
/** Returns the name of the manufacturer of this Gizmo. */
public String getMaker()
{
/* implementation not shown */
}
/** Returns true if this Gizmo is electronic, and false
* otherwise.
*/
public boolean isElectronic()
{
/* implementation not shown */
}
/** Returns true if this Gizmo is equivalent to the Gizmo
* object represented by the
* parameter, and false otherwise.
*/
public boolean equals(Object other)
{
/* implementation not shown */
}
// There may be instance variables, constructors, and methods not shown.
}
The OnlinePurchaseManager class manages a sequence of Gizmo objects that an individual has purchased from an online vendor. You will write two methods of the OnlinePurchaseManager class. A partial definition of the OnlinePurchaseManager class is shown below.
public class OnlinePurchaseManager
{
/** An ArrayList of purchased Gizmo objects,
* instantiated in the constructor.
*/
private ArrayList<Gizmo> purchases;
/** Returns the number of purchased Gizmo objects that are electronic
* whose manufacturer is maker, as described in part (a).
*/
public int countElectronicsByMaker(String maker)
{
/* to be implemented in part (a) */
}
/** Returns true if any pair of adjacent purchased Gizmo objects are
* equivalent, and false otherwise, as described in part (b).
*/
public boolean hasAdjacentEqualPair()
{
/* to be implemented in part (b) */
}
// There may be instance variables, constructors, and methods not shown.
}
- Write the countElectronicsByMaker method. The method examines the ArrayList instance variable purchases to determine how many Gizmo objects purchased are electronic and are manufactured by maker.
Assume that the OnlinePurchaseManager object opm has been declared and initialized so that the ArrayList purchases contains Gizmo objects as represented in the following table.
| Index in purchases | 0 | 1 | 2 | 3 | 4 | 5 |
| Value returned by method call isElectronic() | true | false | true | false | true | false |
| Value returned by method call getMaker() | "ABC" | "ABC" | "XYZ" | "lmnop" | "ABC" | "ABC" |
The following table shows the value returned by some calls to countElectronicsByMaker.
| Method Call | Return Value |
| opm.countElectronicsByMaker("ABC") | 2 |
| opm.countElectronicsByMaker("lmnop") | 0 |
| opm.countElectronicsByMaker("XYZ") | 1 |
| opm.countElectronicsByMaker("QRP") | 0 |
Complete method countElectronicsByMaker below.
/** Returns the number of purchased Gizmo objects that are electronic and
* whose manufacturer is maker, as described in part (a).
*/
public int countElectronicsByMaker(String maker)
- When purchasing items online, users occasionally purchase two identical items in rapid succession without intending to do so (e.g., by clicking a purchase button twice). A vendor may want to check a user’s purchase history to detect such occurrences and request confirmation.
Write the hasAdjacentEqualPair method. The method detects whether two adjacent Gizmo objects in purchases are equivalent, using the
equals method of the Gizmo class. If an adjacent equivalent pair is found, the hasAdjacentEqualPair method returns true. If no such pair is found, or if purchases has fewer than two elements, the method returns false.
Complete method hasAdjacentEqualPair below.
/** Returns true if any pair of adjacent purchased Gizmo objects are
* equivalent, and false otherwise, as described in part (b).
*/
public boolean hasAdjacentEqualPair()