ITEC120 exam01-practice

exam01-practice

This is a sample exam, based on a previous semester. Although it represents most of the major topics we've covered, it doesn't necessarily cover everything that will be on this semester's exam.

This exam is closed-book, 50-minutes.

You may use any of the functions on the provided documentation for Object120;

You may presume any code you write on this exam is inside class Exam01 extends Object120 { … }.

(5pts) What Java type is most appropriate, to represent each of the following pieces of information — boolean, int, double, char, or String?

The price of some medicine, in dollars. double
The price of some medicine, in cents. int
Instructions on how frequently to take some medicine (e.g. 3 times per day, once a month, before every meal, at age 5 only (like the Mumps vaccine), etc.). String
A person's weight, in kg. double
The weight of some medicine, in mg. double

(3pts) How many implicit type-conversions are happening in the following code? 2
System.out.println( "Hi-ho " + Math.sqrt(16) )
Re-write the statement, making the conversions explicit (using functions in Object120): System.out.println( "Hi-ho " + doubleToString( Math.sqrt( intToDouble(16) ) ) )

(1pt) In Java, + can mean one of two different functions, depending on context. What are they? addition; string-concatenation

(1pt) In Java, / can mean one of two different functions ¹, depending on context. What are they? floating-point division; quotient

(3pts) What is the result of the following expressions, in Java? (No calculator needed.) Include a decimal point in your answer only if the result is a double. Ignore any round-off error.

2+7/3*6+1 15
2.0+7/3*6.0+1 15.0
2.0+7.0/3.0*6.0+1 17.0

(6pts) What is the result of the following expressions, in Java? Include quotation-marks in your answer only if the result is a String.

toUpperCase( "hee" + "haw" ) "HEEHAW"
toUpperCase( "hee" ) + "haw" "HEEhaw"
toUpperCase( substring( "howdy", 1, 3) ) + "ch" "OWch"
length(toUpperCase( substring("howdy", 1, 3) )) + "ch" "2ch"
substring( "howdy", 1, length("folk")+1 ) "owdy"
substring( "howdy", 1, length("folk") ) + 1 "owd1"

(3pts) Browsing through the on-line Java documentation, you find a class TimeZone, you see the following ²:

static boolean

inDaylightTime( String country, int year, int month, int day )
Determine whether the given date is in daylight savings time, for the given country.

Call this function, to find whether Peru is observing daylight savings time today.

inDaylightTime( "Peru", 2010, 10, 1 );

Suppose there were a function isFrabjous which takes in an double and a String (in that order), and returns a boolean.

(2pts) Declare a variable which could hold the result of calling isFrabjous. boolean isFrab;
(2pts) Call isFrabjous, passing it 12.3 and aloha, and store the result in the variable you declared in (a):

isFrab = isFrabjous( 12.3, "aloha" )
(2pts) Write the signature for isFrabjous. boolean isFrabjous( double x, String s )

(1pt) To see if two Strings are the same, use the function equals .
(1pt) To see if two chars are the same, use == .
(1pt) When initializing a variable, use = between the variable-name and the expression.

(1pt) Write an expression determining whether a (already-initialized) variable s has the value "Wumpus". equals(s,"Wumpus")

We will write a function hasPrefix which is given two Strings, and determines whether the first starts with the second. For example ³, catheter has cat as a prefix, and also catheter has ca as a prefix, but catheter does not have cathy as a prefix.

(4pts) Complete the following with three plausible test cases which are different from any of the ones suggested above:

  static void testHasPrefix() {

    System.out.println( "Actual : " +   hasPrefix( "professor", "pro" )   );

    System.out.println( "Desired: " +                         true                         );


    System.out.println( "Actual : " +   hasPrefix( "pro", "professor"   );

    System.out.println( "Desired: " +                       false                       );


    System.out.println( "Actual : " +   hasPrefix( "prof", "prof")   );

    System.out.println( "Desired: " +                         true                         );
  }

Solution: Tests where the first input string is shorter that the second, equal-length to the second, and longer than the second are all good. Also, further tests involving the empty string would be in order.

(3pts) Complete the signature for hasPrefix in the space provided below.
(4pts) Complete the body for hasPrefix in the space provided below.
hint: When calling substring, be sure that the indices you provide aren't bigger than the length of the string you're extracting the substring from!

  // (b) Signature here

  static   boolean     hasPrefix  (    String             s1         ,  



   String             s2          ) {


   // (c) Body here

    if (length(s1) < length(s2)) {
      return false;
    }
    else {
      return equals( substring(s1,0,length(s2)), s2 );
    }







   }

Solution: By the way, you might recall from lecture that: whenver an if-else has a boolean literal as an answer (in this case, false in the first branch), it can be simplified using the boolean operators &&, ||, !.&& In this case we could also return (length(s1) ≥ length(s2)) && equals( substring(s1,0,length(s2)), s2). (In fact, this java code even reads nicely out loud -- practically English.)

You want to advertise your company, and have purchased a list of a million names and addresses. However, when you start to browse the list you see that some names include a title (either Mr. or Dr., nothing else), and some don't. You need to write a function which takes in the entire name as one String, and adds the title ⁴ Mr. if the name didn't already include either Dr. or Mr.. For example, here are some test cases your code must pass:

    static void testAddTitleIfNeeded() {
      System.out.println( "Actual : " + addTitleIfNeeded( "Mr. Oscar Grouch" ) );
      System.out.println( "Desired: " + "Mr. Oscar Grouch" ); // no need to add title

      System.out.println( "Actual : " + addTitleIfNeeded( "Dr. B. Burner" ) );
      System.out.println( "Desired: " + "Dr. B. Burner" ); // no need to add title

      System.out.println( "Actual : " + addTitleIfNeeded( "Big Bird" ) );
      System.out.println( "Desired: " + "Mr. Big Bird" ); // NEED to add title

      System.out.println( "Actual : " + addTitleIfNeeded( "T" ) );
      System.out.println( "Desired: " + "Mr. T" ); // NEED to add title
    }

Below, write the signature (2pts) and body (5pts) for addTitleIfNeeded. Even if you didn't finish the previous problem, you may assume that hasPrefix works correctly.

static String addTitleIfNeeded( String name ) {
    if (hasPrefix(name,"Mr. ") || hasPrefix(name,"Dr. ")) {
      return name;  // make no changes
    }
    else {
      return "Mr. " + name;
    }
  }

Note that there are other ways to write this function as well, but using hasPrefix as a helper makes the code easier to write and to read. If you really wanted to factor out the return and codify Mr. as the standard title, you could re-factor the above to:

  String addTitleIfNeeded( String name ) { 
    final String STD_TITLE = "Mr. ";
    String additionalTitle;
    if (hasPrefix(name,STD_TITLE) || hasPrefix(name,"Dr. ")) {
      additionalTitle = "";
    }
    else {
      additionalTitle = STD_TITLE;
    }
    return additionalTitle + name;
  }

In the version, I'm not entirely happy with including the space as part of STD_TITLE, but it's kinda overkill to include it elsewhere.

¹ Comments aren't functions. ↩

² In truth, whether you observe daylight savings can vary within a country; the actual Java classes tend to use a Locale instead of a country-name. Also, in real life inDaylightTime is actually a non-static method, but I made it static for the purposes of this exam. ↩

³ If you want a technical definition: String s1 has String s2 as a prefix if there is a solution to the equation equals(s1,s2+x) (where we are solving for x, which must be a String). ↩

⁴ It turns out the list of names only includes males. You might be having second thoughts about the sleaziness of the person you bought the list of names from! However, this does make your code a bit easier. ↩

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