Short PD Post Test

Section 6.1 Short PD Post Test

This is a short PD post test.

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Exercises Exercises

1.

Unit 1 Output:

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Practice 3.D: Explain why a code segment will not compile or work as intended.
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LO 1.3.A: Develop code to generate output and determine the result that would be displayed
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Consider the following code segment.

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System.out.print(Take all the courses in your curriculum.);
System.out.println(Ask questions.);
System.out.println(--Katherine Johnson);

The code segment is intended to produce the following output but does not work as intended.

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Take all the courses in your curriculum. Ask questions.
--Katherine Johnson

Which changes should be made so that the code segment produces the intended output?

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I.   In line 1, print should be changed to println.
II.  In lines 1, 2, and 3, print should be capitalized.
III. In lines 1, 2, and 3, the text inside the parentheses should be in quotation marks.

I only
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print is correct since a new line is not printed after the first line of output.
II only
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Only class names like System are capitalized.
III only
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Correct.
I and II
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I and II are not correct.
I and III
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print is correct since a new line is not printed after the first line of output.

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2.

Unit 1 Expressions:

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LO 1.3.C Develop code for arithmetic expressions and determine the result of these expressions.
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LO 1.4.A Develop code for assignment statements with expressions and determine the value that is stored in the variable as a result of these statements.
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Practice 3.A: Determine the result or output based on statement execution order in an algorithm.
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Consider the following code segment:

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int x = 16;
double y = 8.0;
int z = 2;
x = x / 5;
y += x;
y = y * z;

What is the value in variable y when the code segment is executed?

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2
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Trace through the code keeping track of the variable values.
8
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Trace through the code keeping track of the variable values.
11
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Trace through the code keeping track of the variable values.
22.0
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Correct. Integer division is used.
22.4
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Integer division is used since x is an int.

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3.

Unit 1 Objects:

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Practice 2.B: Write program code involving data abstractions.
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LO 1.13.C Develop code to create an object by calling a constructor.
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Consider the following code segment.

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public class Party
{
    private int numInvited;
    private boolean partyCancelled;

    public Party()
    {
        numInvited = 1;
        partyCancelled = false;
    }

    public Party(int invites)
    {
        numInvited = invites;
        partyCancelled = false;
    }
}

Which of the following code segments, when placed in a method in a class other than the Party class, correctly creates a new object of the Party class with 20 people invited?

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I.   Party myParty.numInvited = 20;
II.  Party ourParty = new Party(20);
III. Party otherParty = new Party();
     otherParty.numInvited = 20;

I only
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Private instance variables like numInvited are not accessible outside of the class.
II only
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Correct. The constructor initializes the private instance variable.
III only
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Private instance variables like numInvited are not accessible outside of the class.
II and III
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Private instance variables like numInvited are not accessible outside of the class.
I, II, and III
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Private instance variables like numInvited are not accessible outside of the class.

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4.

Unit 1 Methods:

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LO 1.14.A Develop code to call instance methods and determine the result of these calls.
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LO 1.12.A: Explain the relationship between a class and an object.
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Consider the following class.

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public class Liquid
{
    private double freezingPoint;
    private double currentTemp;

    public Liquid()
    {
        freezingPoint = 0;
        currentTemp = 0;
    }

    public void lowerTemp(double degrees)
    {
        currentTemp -= degrees;
    }

    public void raiseTemp(double degrees)
    {
        currentTemp += degrees;
    }

    void freeze()
    {
        currentTemp = freezingPoint;
    }
}

Assume that the following Liquid object has been declared.

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Liquid liquid = new Liquid();

Which of the following statements is valid?

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Liquid.freezingPoint;
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Private non-static instance variables like freezingPoint are not accessible outside of the class.
liquid.currentTemp();
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currentTemp is not a method.
liquid.lowerTemp();
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The lowerTemp method requires an argument.
liquid.raiseTemp(10);
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Correct!
liquid.freeze(10)
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The freeze method does not have a parameter.

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5.

Unit 2 Selection:

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LO 2.2.A: Develop code to create Boolean expressions with relational operators and determine the result of these expressions.
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Practice 3.A: Determine the result or output based on statement execution order in an algorithm.
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Consider the following code segment. Assume boolean variables p and q have been initialized.

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if (!p || q)
{
  System.out.print("winner");
}

For what values of p and q will “winner” be printed?

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“winner” will be printed when p is false, regardless of the value of q.
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The boolean expression is not p or q.
“winner” will be printed when q is false, regardless of the value of p.
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p has to be false or q has to be true.
“winner” will be printed only when p is false and q is true.
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|| means or, not and.
“winner” will always be printed.
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p has to be false or q has to be true.
“winner” will never be printed.
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It will be printed if p is false or q is true.

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6.

Unit 2 Selection:

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LO 2.3.A Develop code to represent branching logical processes by using selection statements and determine the result of these processes.
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LO 2.4.A Develop code to represent nested branching logical processes and determine the result of these processes.
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Consider the following code segment.

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int a = 100;
int b = 90;
if (a >= 100)
{
   if (b > 100)
   {
      System.out.print("go ");
   }
   else if (b > 90)
   {
     System.out.print("it ");
   }
   else
   {
      System.out.print("up ");
   }
}
System.out.print("on ");

What is printed when the code segment above is executed?

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go on
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b is not greater than 100.
it up on
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b is not greater than 90.
it on
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b is not greater than 90.
up on
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Correct.
on
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The first if statement is true since a is = 100.

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7.

Unit 2 Loops:

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LO 2.8.A Develop code to represent iterative processes using for loops and determine the result of these processes.
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Complete the loop below by filling in the missing code. The loop should calculate the number of leap years between the variables year1 and year2, inclusive, using a helper method isLeapYear(year) which returns true if year is a leap year and false otherwise.

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int year1 = 2000;
int year2 = 2020;
int count = 0;

/* Missing Code */
{
      if (isLeapYear(y))
          count++;
}

for (int year1 = 2000; int year2 = 2020; count++)
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The for-loop should initialize, test, and increment the loop variable y.
for (int y = year2 - year1; y < year2; y++)
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y should start counting from year1.
for (int y = year1; y <= year2; y++)
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Correct. The for loops counts from year1 to year2.
for (int year1 = 2000; year1 < year2; year1++)
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The for-loop should initialize, test, and increment the loop variable y.
for (int year1; year2; count++)
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The for-loop should initialize, test, and increment the loop variable y.

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8.

Unit 4 Loops and Strings:

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LO 2.10.A Develop code for standard and original algorithms that involve strings and determine the result of these algorithms.
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Consider the following method.

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public static String changeStr(String str)
{
     String result = "";
     for (int i = 1; i < str.length() - 1; i += 2)
     {
          result += str.substring(i, i + 1);
     }
     return result;
}

What value is returned as a result of the method call changeStr(“ABCDE”)?

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“ABCDE”
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The for-loop increments the string index i by 2’s, visiting every other character.
“BCDE”
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The for-loop increments the string index i by 2’s, visiting every other character.
“AC”
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The character A is at index 0, but the loop starts at index 1.
“BD”
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Correct. The for-loop increments the string index i by 2’s, visiting every other character, starting at index 1 (the second character).
“ACE”
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The character A is at index 0, but the loop starts at index 1.

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9.

Unit 3 Class Creation:

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LO 3.3.A Develop code to designate access and visibility constraints to classes, data, constructors, and methods.
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LO 3.4.A Develop code to declare instance variables for the attributestobeinitializedin the body of the constructors of a class.
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Consider the following class Cat:

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public class Cat
{
    /* missing code */
}

Which of the following replacements for the missing code is the most appropriate implementation of a class Cat which contains attributes for the cat’s name and age and a constructor?

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public String name;
public int age;
public Cat(String name, int age)
{
  name = name;
  age = age;
}

The parameters of the constructor cannot be the same variables as the instance variables, and the instance variables should be private.

private String name;
private int age;
public Cat(String n, int a)
{
  name = n;
  age = a;
}

Correct. The constructor initializes the instance variables to the parameter variables.

public String name;
public int age;
public Cat(String n, int a)
{
  name = n;
  age = a;
}

The instance variables should be private.

private String name;
private int age;
public Cat(String n, int a)
{
  n = name;
  a = age;
}

name should be set to n, not the n to name.

public String name;
public int age;
public Cat(String n, int a)
{
  n = name;
  a = age;
}

name should be set to n, not the n to name, and the instance variables should be private.

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10.

Unit 3 Class Creation:

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LO 3.5.A Develop code to define behaviors of an object through methods written in a class using primitive values and determine the result of calling these methods.
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Which of the following is the most appropriate header for a method that would set the value of the private instance variable y?

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private int setY(int value)
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The set method should be public.
private void setY()
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The set method should be public.
public int setY()
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The set method needs a parameter to set y to.
public void setY()
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The set method needs a parameter to set y to.
public void setY(int value)
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Correct. The public set method sets the instance variable y to the parameter value.

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11.

Unit 3 Class Creation:

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Practice 3.C: Determine the result or output based on code that contains procedural abstractions.
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Practice 3.D: Explain why a code segment will not compile or work as intended and modify the code to correct the error.
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LO 3.5.A Develop code to define behaviors of an object through methods written in a class using primitive values and determine the result of calling these methods.
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Consider the following class definition. The class does not compile.

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public class Student
{
    private int id;

    public void getId()
    {
        return id;
    }
}

The accessor method getId is intended to return the id of a Student object. Which of the following best explains why the class does not compile?

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The getId method should be declared as private.
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It should be public.
The getId method should have a parameter.
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It does not need a parameter.
The getId method should not return a value.
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It needs to return id.
The getId method should not have a return type.
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It needs a return type for the value it returns.
The getId method should have int as its return type.
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Correct.

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12.

Unit 4 Arrays:

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LO 4.3.A Develop code used to represent collections of relateddatausingonedimensional (1D) array objects.
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LO 4.4.A Develop code used to traverse the elements in a 1D array and determine the result of these traversals.
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Consider an integer array which has been declared and initialized with one or more integer values such as:

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int[] array =  { 10, 20, 30 };

Which of the following code segments doubles all the values in the array?

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I. int i = 0;
   while (i < array.length)
   {
       array[i] *= 2;
   }
II. for (int i = 0; i < array.length; i++)
    {
        array[i] *= 2;
    }
III. for (int i = 1; i <= array.length; i++)
     {
          array[i] *= 2;
     }

I only
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This is an infinite loop. i needs to be incremented.
II only
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Correct.
III only
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This loop will give an index out of bounds error. Arrays are indexed starting at 0 and up until array.length.
I and II only
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I is an infinite loop. i needs to be incremented.
I, II, and III
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I is an infinite loop. III will have an array index out of bounds error.

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13.

Unit 4 Arrays:

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LO 4.4.A Develop code used to traverse the elements in a 1D array and determine the result of these traversals.
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LO 4.5.A Develop code for standard and original algorithms for a particular context or specification that involves arrays and determine the result of these algorithms.
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Consider the following method. Which of the following statements best describes when it returns true?

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public boolean mystery(int array[], int value)
{
     boolean temp = false;
     for (int i = 0; i < array.length; i++)
     {
        temp = (array[i] == value);
     }
     return temp;
}

Whenever the first element in array is equal to value
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temp will change its value as each element in the array is visited.
Whenever array contains any element which equals value
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temp will change its value as each element in the array is visited, so it may change after finding an element which equals value.
Whenever the last element in array is equal to value
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Correct. temp will change its value as each element in the array is visited.
Whenever more than 1 element in array is equal to value
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If the 1 element is the last element, it will still return true.
Whenever exactly 1 element in array is equal to value
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Many elements can be equal to value, as long as the last one is equal.

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