ITEC 120 2007spring ibarland, jpittges

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lab02a
lab02a
Strings

We'll experiment with Strings, which were introduced in lecture yesterday.

Today's project will be done in pairs.

If you didn't finish last week's lab, raise your hand at the start of this lab, and a PI will look at it.

A function with two inputs: example

Today we'll write a function which takes in two inputs. It's not a big deal, but we technically haven't mentioned it in Lecture. (Although you did use it on hw00!) Here's an example of a function taking two inputs:

/**  Return the cost of ordering several pizzas of a given size.
 * @param numPizzas THe number of pizzas ordered.
 * @param size The size (diameter) of the pizzas orderd, in inches.
 * @return The total price of the order, dollars.
 * Examples:
 *  ps.costOfMany( 1, 16 ) =~  6.03
 *  ps.costOfMany( 3, 16 ) =~ 18.09
 *  ps.costOfMany( 0, 16 ) =   0
 *  ps.costOfMany( 7,  0 ) =   0
 */
double costOfMany( int numPizzas, double size ) {
  return numPizzas * this.pizzaArea(size) * 0.03;
  // 0.03 is the price per square inch of pizza, in dollars.
  // Note that the price may change, in the future.
  }

typereturn namefunction( typeparam1 nameparam1, typeparam2 nameparam2 ) {
  return expression;
  }

Write String literals in quotes

In lecture, we saw functions dealing with Strings. When you call them in BlueJ, be sure to include quotation marks around the letters you want to string together:

jo.echo2( "hello" )

jo.echo2( hello )   /* error -- cannot find variable hello */

Today's task

Preliminary:

• Start up BlueJ.
• Create a new project; a plausible name would be “lab-week2a” or so.
• Make a new class Emcee; as before, take the file which BlueJ provides (with a few boilerplate definitions) and gut it out, replacing it with a single class definition, perhaps

  class Emcee { }

Experimenting on Strings

Go to BlueJ's code pad in the lower-right corner of the main screen¹. Type in some sample strings, such as:

• "hello"
• "!&$^%, and &*(# too!"
• ""

As just discussed in the lecture yesterday, +, if applied to Strings, will concatenate them. Try these in the Code Pane:

• "hi" + "there"
• "Ja" + "va a la" + "ng" + "u" + "age."
• Write a method which, given any name, will return an introduction for that name. That is:

  /** Give a string suitable for introducing a certain name. * @param name The name of the person being introduced. * @return a mundane introduction. * Examples (if mcJo were an instance of class Emcee): * mcJo.introduce( "Snowball III" ) = "Hello, world; my name is Snowball III." * mcJo.introduce( "007" ) = "Hello, world; my name is 007." * mcJo.introduce( "" ) = "Hello, world; my name is ." */

  The standard steps of approaching a problem:
  1. Test cases. Three are already provided for you; paste those into your code, and write at least one of your own
  2. Write the signature of the function: remember the mantra for declaring a function, “returnType-functionName-openParen-paramName&type”
  3. Javadoc comments. Explain the meaning of each parameter, and what is returned.
  4. Finally, fill in the body of the function (return-expression-semicolon).
  5. Test your function by calling the actual test cases written above.
• Test introduce by creating an instance of class Emcee (by right-clicking on the tan class-definition-box). Name it, say, “mcJo” (or whatever you like). Then, call your functions in two different ways:
  • Call using BlueJ's menus: right-click on the red instance mcJo. BlueJ then lets you type in a String between the parentheses. Be sure to include quotation marks, so that Java knows you are talking about a String.
  • Call using actual code, from BlueJ's Code Pad. Use the mantra “object dot methodName openParen argument”.

• Agent 007 is known for his suave introduction²: "Bond... James Bond." Write the function introduceSpy, which creates such a greeting, given a first and last name:

  /* Test cases: * mcJo.introduceSpy( "Ian", "Barland" ) = "Barland... *Ian* Barland." * mcJo.introduceSpy( "Dweezil", "Zappa" ) = "Zappa... *Dweezil* Zappa." * mcJo.introduceSpy( "Engelbert", "Humperdinck" ) = "Humperdinck... *Engelbert* Humperdinck." */

  Before you start writing code, write a two more test cases. What are some degenerate inputs to try? (When you have two inputs, you have more choices -- you can have one or the other or both inputs be degenerate.) Pay careful attention to spaces.

  We will check this function off. For full credit, you'll need

  1. at least two other test cases involving degenerate inputs (the empty string);
  2. javadoc: two “@param” lines, and one @return line.
  If you don't finish this program today, have it ready to check off at the start of lab on Friday.

• When you finish (won't be checked off, but is still expected): Lectroid spies all have the first name John. Write a program introduceLectroidSpy which takes in only one input, a last name, and introduces the spy. One test case would be:
  introduceLectroidSpy( "Parker" ) = "Parker... *John* Parker."
  Be sure to make a couple of test cases before starting. Remember the First Law of Programming -- avoid repeated code!
• (Optional, outside of lab:) Some people wonder, how Bond's standard introduction can be modified for people with three names — say, Lewis Scooter Libby.

  • You might say “Libby -- *Lewis Scooter* Libby”. Or, you might say “Scooter Libby -- *Lewis* Scooter Libby”. Choose the approach you prefer, and write a function introduceSpy3, which takes three inputs (first name, middle name, last name), and gives your preferred variant of the answer.

    Remember, don't repeat code!; your solution should not have (for example) an asterisk character anywhere, since that was already up in introduceSpy. This is a tougher problem, but by working through a couple of test cases by hand you should be able to solve it.

  • (Challenge problem!) Some people don't like either of the two variants just mentioned -- because when giving just the (say) “Lewis Scooter” part of their name they could again make that yet more dramatic by saying “Scooter -- *Lewis* Scooter”, as a sub-part of their entire introduction.

    Evaluate each of the two expressions, but first try to work out for yourself what the answers will be:

    mcJo.introduceSpy( "Lewis", mcJo.introduceSpy( "Scooter", "Libby" ) ) mcJo.introduceSpy( mcJo.introduceSpy( "Lewis", "Scooter" ), "Libby" ) )

    Once you understand what those examples are doing, write a function introduceSpyBaroque3 which gives this ornate (convoluted!) introduction for a spy with three names.

  • (A Challenge problem even for ITEC220:) Given a list of names (like ["John", "Jacob", "Jingleheimer", "Schmidt", "Jr."]), write a function introduceSpyBaroque which
    • starts with "Jr.... ",
    is followed by
    • the baroque introduction of the (slightly shorter list of names) ["Jacob", "Jingleheimer", "Schmidt", "Jr."] surrounded by asterisks,
    followed by
    • " Jr.."
    followed by
    • a period.
    We can't do this problem until we (a) learn about Lists, and (b) learn about recursion (since the second step involves solving our entire problem on a slightly shorter list, as a single step of solving the problem on the entire list).

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©2007, Ian Barland, Radford University Last modified 2007.Aug.27 (Mon)

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