AP® Computer Science A Exam Sample Questions: 2020, Exams of Computer Science

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2020 Exam

Sample

Questions

AP

®

COMPUTER SCIENCE A

2020 Exam Sample Question 1

(Adapted from: AP®^ Computer Science A Course and Exam Description) Directions: SHOW ALL YOUR WORK. REMEMBER THAT PROGRAM SEGMENTS ARE TO BE WRITTEN IN JAVA. Notes:

• (^) Assume that the classes listed in the Java Quick Reference have been imported where appropriate.
• (^) Unless otherwise noted in the question, assume that parameters in method calls are not null and that methods are called only when their preconditions are satisfied.
• (^) In writing solutions for each question, you may use any of the accessible methods that are listed in classes defined in that question. Writing significant amounts of code that can be replaced by a call to one of these methods will not receive full credit.

Question 1 - Array/ArrayList

Allotted time: 25 minutes (plus 5 minutes to submit) 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. }

(a) 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) (b) 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()

(c) A programmer would like to add a method getCheapestGizmoByMaker, which returns the least expensive Gizmo purchased by an individual from a given maker. Write a description of how you would change the Gizmo and OnlinePurchaseManager classes in order to support this modification. Make sure to include the following in your response. ཛ (^) Write the method header for the getCheapestGizmoByMaker method. ཛ (^) Identify any new or modified variables, constructors, or methods aside from the getCheapestGizmoByMaker method. Do not write the program code for this change. ཛ (^) Describe, for each new or revised variable, constructor, or method, how it would change or be implemented, including visibility and type. You do not need to describe the getCheapestGizmoByMaker method. Do not write the program code for this change.

(a) Write the isValid method. The method returns true if its parameter numWithCheckDigit, which represents a number containing a check digit, is valid, and false otherwise. The check digit is always the rightmost digit of numWithCheckDigit. The following table shows some examples of the use of isValid. Method Call Return Value Explanation getCheck(159) 2 The check digit for 159 is 2. isValid(1592) true The number 1592 is a valid combination of a number ( 159 ) and its check digit ( 2 ). isValid(1593) false The number 1593 is not a valid combination of a number ( 159 ) and its check digit ( 3 ) because 2 is the check digit for 159. Complete method isValid below. You must use getCheck appropriately to receive full credit. /** Returns true if numWithCheckDigit is valid, or false

• otherwise, as described in part (a)
• Precondition: The number of digits in numWithCheckDigit is
• between two and seven, inclusive.
• numWithCheckDigit >= 0 */ public static boolean isValid(int numWithCheckDigit) (b) A programmer wants to modify the CheckDigit class to keep track of how many times a call to isValid is made with an incorrect check digit. Any time a call to isValid is made with an incorrect check digit, the count should be increased by one. The programmer would like to implement this change without making any changes to the signature of the isValid method or overloading isValid. Write a description of how you would change the CheckDigit class in order to support this modification. Do not write the program code for this change. Make sure to include the following in your response. ཛ (^) Identify any new or modified variables or methods. ཛ (^) Describe, for each new or revised variable or method, how it would change or be implemented, including visibility and type.

Preparing for the AP CSA Open-ended Questions

A single paragraph (2 – 4 sentences) may be sufficient for answering these questions. The provided bullets in the question are meant to guide your single paragraph response; it is not necessary to provide a separate response for each bullet. The following verbs are in addition to the Task Verbs in Free-Response Questions on page 190 of the AP Computer Science A Course and Exam Description :

• (^) Identify : Provide a name for the specific addition or modification as it relates to the problem, without elaboration or explanation. For example, “I need a new variable to represent the item that appears the greatest number of times in the list.”
• (^) Describe : Provide the relevant features or characteristics (including any visibility or type) of your proposed modifications. For example, “I need a new instance variable, which will be a new private String object in the Sample class representing the item that appears the greatest number of times in the list.” This example includes the identification and description necessary for this specific addition. Note that these examples are not responses to the sample questions given but highlight what is expected when students are asked to identify or describe. For features and characteristics of variables, constructors, and methods, see the following topics in the AP Computer Science A Course and Exam Description :
• (^) Variables: 1.2, 2.2, 5.7, 5.
• (^) Constructors: 2.2, 5.
• (^) Methods: 5.4, 5.5, 5.6, 5.7, 5.