ITEC 120 2007fall ibarland, jdymacek

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lect02b
Strings

We have seen two types of data so far, in Java: int, and double. Today we consider a third: Strings.

Strings -- that is, strings of characters in a row -- are Java's name for what most people call text. For example,

• "Yo",
• "I am a String, with a capital S!"
and
• "My length is 16.".

Strings are great for representing various data:

• names of people, like "Engelbert Humperdinck"
• names of inventory items (for example, my grocery receipt reveals that the store's computer uses names like "Cadbry Egg/Drk" to represent the name of Cadbury's Dark Chocolate Egg).
• serial ‘numbers’ like "487WJ2M", confirmation numbers, UPC codes, and ISBN numbers -- all are commonly internally represented as Strings.
• Similarly, zip codes and phone numbers, although they look numeric, are best represented as Strings (since we never multiply them by seven, or subtract them, or otherwise do arithmetic with them).

The empty string

We saw a String with five characters between the quotation marks, and another with two character. Can you write down a String with only one character? Okay, good. How about even shorter than one character? Sure! Type a quotation-mark, then type zero characters, and then the closing quotation-mark:

""

concatenating strings

With numbers, Java has built-in arithmetic functions like + and * (in addition to the special math-package functions Math.sqrt, Math.cos, etc.), so you can start doing fun stuff with numbers immediately. What can we actually do with strings?

It turns out there are many interesting built-in functions on strings, but one which is particularly handy is concatenating strings. In part, it's handy because Java provides a shortcut name for this: +. That is,

"hello" + "there"

"Hello" + " " + "there" + "," + " sailor."

tip: It's easy to forget the + between strings. Spot the missing plus in:

"Hello " + "there" + ", " "Sailor" + " " + "Moon"

Also, it's easy to get 0 or 2 spaces, instead of 1, when doing a lot of string concatenation.

Just as 0 and 1 are numbers that are particular easy to compute with, the empty string, "", is particularly easy to concatentate. Always use "" as a test case, unless that's a clearly nonsensical test case.

Exercise: Complete the following function, using + for Strings:

/** Return the sound of an echo, of a given phrase.
 * @param _____ The phrase to shout at a cliff-side.
 * @return The sound returned
 *    p.echo2( "hello" ) = "hello, hello."
 *    p.echo2( "Who's there?" ) = "Who's there?, Who's there?."
 *    p.echo2( "z" ) = ______
 *    p.echo2( "" )  = ______
 */
_____ echo2( _____ _____ ) {
  return ____________________________;
  }

Exercise:

/** Return something Beavis might say, in response to just 
 *  about any trigger word.
 * @param _____ The trigger word, for Beavis's response.
 * @return Beavis's catchphrase.
 *    p.beavis( "but" ) = "Heh heh, you said 'but'."
 *    p.beavis( "phenylalanine" ) = "Heh heh, you said 'phenylalanine'."
 *    p.beavis( "" ) = "Heh heh, you said ''."
 */
_____ beavis( _____ _____ ) {
  return ____________________________;
  }

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©2007, Ian Barland, Radford University Last modified 2007.Aug.30 (Thu)

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