Computer Science Chapter 5
Consider the following method. /* missing precondition */ public void someMethod(int j, int k, String oldString) { String newString = oldString.substring(j, k); System.out.println("New string: " + newString); } Which of the following is the most appropriate precondition for someMethod so that the call to substring does not throw an exception?
/* Precondition: 0 <= j <= k <= oldString.length() */
Consider the following class definition. public class Person { private String name; private int feet; private int inches; public Person(String nm, int ft, int in) { name = nm; feet = ft; inches = in; } public int heightInInches() { return feet * 12 + inches; } public String getName() { return name; } public String compareHeights(Person other) { if (this.heightInInches() < other.heightInInches()) { return name; } else if (this.heightInInches() > other.heightInInches()) { return other.getName(); } else return "Same"; } } The following code segment appears in a method in a class other than Person. Person andy = new Person("Andrew", 5, 6); Person ben = new Person("Benjamin", 6, 5); System.out.println(andy.compareHeights(ben)); What, if anything, is printed as a result of executing the code segment?
Andrew
Consider the following class definition, which represents two scores using the instance variables score1 and score2. The method reset is intended to set to 0 any score that is less than threshold. The method does not work as intended. public class TestClass { private int score1; private int score2; public TestClass(int num1, int num2) { score1 = num1; score2 = num2; } public void reset(int threshold) { if (score1 < threshold) // line 14 { score1 = 0; // line 16 } else if (score2 < threshold) // line 18 { score2 = 0; } } } Which of the following changes can be made so that the reset method works as intended?
In line 18, change else if to if.
Consider the following class definition. public class Gadget { private static int status = 0; public Gadget() { status = 10; } public static void setStatus(int s) { status = s; } } The following code segment appears in a method in a class other than Gadget. Gadget a = new Gadget(); Gadget.setStatus(3); Gadget b = new Gadget(); Which of the following best describes the behavior of the code segment?
The code segment creates two Gadget objects a and b. The class Gadget's static variable status is set to 10, then to 3, and then back to 10.
Consider the following class declaration. public class Student { private String firstName; private String lastName; private int age; public Student(String firstName, String lastName, int age) { firstName = firstName; lastName = lastName; age = age; } public String toString() { return firstName + " " + lastName; } } The following code segment appears in a method in a class other than Student. It is intended to create a Student object and then to print the first name and last name associated with that object. Student s = new Student("Priya", "Banerjee", -1); System.out.println(s); Which of the following best explains why the code segment does not work as expected?
The code segment will compile, but the instance variables will not be initialized correctly because the variable names firstName, lastName, and age refer to the local variables inside the constructor.
Consider the following class declaration. public class Student { private String name; private int age; public Student(String n, int a) { name = n; age = a; } public boolean isOlderThan5() { if (age > 5) { return true; } } } Which of the following best describes the reason this code segment will not compile?
The isOlderThan5 method is missing a return statement for the case when age is less than or equal to 5
Consider the following class. public class Help { private int h; public Help(int newH) { h = newH; } public double getH() { return h; } } The getH method is intended to return the value of the instance variable h. The following code segment shows an example of creating and using a Help object. Help h1 = new Help(5); int x = h1.getH(); System.out.println(x); Which of the following statements best explains why the getH method does not work as intended?
The getH method should have a return type of int.
Consider the following class definition. public class ClassP { private String str; public ClassP(String newStr) { String str = newStr; } } The ClassP constructor is intended to initialize the str instance variable to the value of the formal parameter newStr. Which of the following statements best describes why the ClassP constructor does not work as intended?
The variable str should not be declared as a String in the constructor.
The method addItUp(m, n) is intended to print the sum of the integers greater than or equal to m and less than or equal to n. For example, addItUp(2, 5) should return the value of 2 + 3 + 4 + 5. /* missing precondition */ public static int addItUp(int m, int n) { int sum = 0; for (int j = m; j <= n; j++) { sum += j; } return sum; } Which of the following is the most appropriate precondition for the method?
/* Precondition: m <= n */
Consider the following method substringFound, which is intended to return true if a substring, key, is located at a specific index of the string phrase. Otherwise, it should return false. public boolean substringFound(String phrase, String key, int index) { String part = phrase.substring(index, index + key.length()); return part.equals(key); } Which of the following is the best precondition for index so that the method will return the appropriate result in all cases and a runtime error can be avoided?
0 <= index < phrase.length() - key.length()
Consider the following class definition. public class Contact { private String contactName; private String contactNumber; public Contact(String name, String number) { contactName = name; contactNumber = number; } public void doSomething() { System.out.println(this); } public String toString() { return contactName + " " + contactNumber; } } The following code segment appears in another class. Contact c = new Contact("Alice", "555-1234"); c.doSomething(); c = new Contact("Daryl", ""); c.doSomething(); What is printed as a result of executing the code segment?
Alice 555-1234 Daryl
Consider the following class definition. Each object of the class Employee will store the employee's name as name, the number of weekly hours worked as wk_hours, and hourly rate of pay as pay_rate. public class Employee { private String name; private int wk_hours; private double pay_rate; public Employee(String nm, int hrs, double rt) { name = nm; wk_hours = hrs; pay_rate = rt; } public Employee(String nm, double rt) { name = nm; wk_hours = 20; pay_rate = rt; } } Which of the following code segments, found in a class other than Employee, could be used to correctly create an Employee object representing an employee who worked for 20 hours at a rate of $18.50 per hour? I. Employee e1 = new Employee("Lili", 20, 18.5); II. Employee e2 = new Employee("Steve", 18.5); III. Employee e3 = new Employee("Carol", 20);
I and II only
Consider the following class definition. public class BoolTest { private int one; public BoolTest(int newOne) { one = newOne; } public int getOne() { return one; } public boolean isGreater(BoolTest other) { /* missing code */ } } The isGreater method is intended to return true if the value of one for this BoolTest object is greater than the value of one for the BoolTest parameter other, and false otherwise. The following code segments have been proposed to replace /* missing code */. I. return one > other.one; II. return one > other.getOne(); III. return getOne() > other.one; Which of the following replacements for /* missing code */ can be used so that isGreater will work as intended?
I, II and III
Consider the class definition below. The method levelUp is intended to increase a Superhero object's strength attribute by the parameter amount. The method does not work as intended. public class Superhero { private String name; private String secretIdentity; private int strength; public Superhero(String realName, String codeName) { name = realName; secretIdentity = codeName; strength = 5; } public int levelUp(int amount) // line 14 { strength += amount; // line 16 } } Which of the following changes should be made so that the levelUp method works as intended?
In line 14, levelUp should be declared as type void
Consider the following class, which models a bank account. The deposit method is intended to update the account balance by a given amount; however, it does not work as intended. public class BankAccount { private String accountOwnerName; private double balance; private int accountNumber; public BankAccount(String name, double initialBalance, int acctNum) { accountOwnerName = name; balance = initialBalance; accountNumber = acctNum; } public void deposit(double amount) { double balance = balance + amount; } } What is the best explanation of why the deposit method does not work as intended?
In the deposit method, the variable balance is declared as a local variable and is different from the instance variable balance.
Consider the following class definition. The method appendIt is intended to take the string passed as a parameter and append it to the instance variable str. For example, if str contains "week", the call appendIt("end") should set str to "weekend". The method does not work as intended. public Class StringThing { private String str; public StringThing(String myStr) { str = myStr; } public void appendIt(String s) // line 10 { str + s; // line 12 } } Which of the following changes should be made so that the appendIt method works as intended?
Line 12 should be changed to str = str + s;
Consider the following class declaration. The changeWeather method is intended to update the value of the instance variable weather and return the previous value of weather before it was updated. public class WeatherInfo { private String city; private int day; private String weather; public WeatherInfo(String c, int d, String w) { city = c; day = d; weather = w; } public String changeWeather(String w) { /* missing code */ } } Which of the following options should replace /* missing code */ so that the changeWeather method will work as intended?
String prev = weather;weather = w;return prev;
Consider the following definition of the class Student. public class Student { private int grade_level; private String name; private double GPA; public Student (int lvl, String nm, double gr) { grade_level = lvl; name = nm; GPA = gr; } } Which of the following object initializations will compile without error?
Student max = new Student (10, "Max", 3.75);
Consider the following class definition. public class Pet { private String name; private int age; public Pet(String str, int a) { name = str; age = a; } public getName() { return name; } } Which choice correctly explains why this class definition fails to compile?
The accessor method is missing a return type.
The following class is used to represent shipping containers. Each container can hold a number of units equal to unitsPerContainer. public class UnitsHandler { private static int totalUnits = 0; private static int containers = 0; private static int unitsPerContainer = 0; public UnitsHandler(int containerSize) { unitsPerContainer = containerSize; } public static void update(int c) { containers = c; totalUnits = unitsPerContainer * containers; } } The following code segment appears in a method in a class other than UnitsHandler. Assume that no other code segments have created or modified UnitsHandler objects. UnitsHandler large = new UnitsHandler(100); UnitsHandler.update(8); Which of the following best describes the behavior of the code segment?
The code segment creates a UnitsHandler object called large and sets the static variables unitsPerContainer, containers, and totalUnits to 100, 8, and 800, respectively.
Consider the following class definition. public class Email { private String username; public Email(String u) { username = u; } public void printThis() { System.out.println(this); } public String toString() { return username + "@example.com"; } } The following code segment appears in a method in another class. Email e = new Email("default"); e.printThis(); What, if anything, is printed as a result of executing the code segment?
Consider the following class. The method getTotalSalaryAndBonus is intended to return an employee's total salary with the bonus added. The bonus should be doubled when the employee has 10 or more years of service. public class Employee { private String name; private double salary; private int yearsOfService; public Employee(String n, double sal, int years) { name = n; salary = sal; yearsOfService = years; } public double getTotalSalaryAndBonus(double bonus) { /* missing code */ } } Which of the following could replace /* missing code */ so that method getTotalSalaryAndBonus will work as intended?
if (yearsOfService >= 10){bonus *= 2;}return salary + bonus;
Consider the following class definition. public class Beverage { private int numOunces; private static int numSold = 0; public Beverage(int numOz) { numOunces = numOz; } public static void sell(int n) { /* implementation not shown */ } } Which of the following best describes the sell method's level of access to the numOunces and numSold variables?
numSold can be accessed and updated; numOunces cannot be accessed or updated.
The Thing class below will contain a String attribute, a constructor, and the helper method, which will be kept internal to the class. public class Thing { /* missing code */ } Which of the following replacements for /* missing code */ is the most appropriate implementation of the class?
private String str;public Thing(String s){ / implementation not shown / }private void helper(){ / implementation not shown / }
The Fraction class below will contain two int attributes for the numerator and denominator of a fraction. The class will also contain a method fractionToDecimal that can be accessed from outside the class. public class Fraction { /* missing code */ // constructor and other methods not shown } Which of the following replacements for /* missing code */ is the most appropriate implementation of the class?
private int numerator;private int denominator;public double fractionToDecimal(){return (double) numerator / denominator;}
Consider the following class definition. public class Person { private String name; /* missing constructor */ } The statement below, which is located in a method in a different class, creates a new Person object with its attribute name initialized to "Washington". Person p = new Person("Washington"); Which of the following can be used to replace /* missing constructor */ so that the object p is correctly created?
public Person(String n) { name = n; }
The Employee class will contain a String attribute for an employee's name and a double attribute for the employee's salary. Which of the following is the most appropriate implementation of the class?
public class Employee{private String name;private double salary;// constructor and methods not shown}