ITEC 120 2010fall ibarland

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lab12a
array practice I

We will practice today creating arrays (as in lect11b—arrays), and writing methods take in and/or return arrays. You won't submit these programs, but writing them will will help you with writing the code for hw09.

Do not use BlueJ; instead use a text editor and the command-line programs java and javac, as we learned last week.

• Create a new directory (say) lab12-proj. We'll put today's files inside there.
• Just to get started, create a class Lab12 with a public static void main( String[] args ) method that (for now) just prints out a greeting.
  (Be sure to use these names exactly).

• Write a method createData which takes in an int n, and returns a brand new array of n doubles where (for each legal index i) the ith location contains i/2. (Should this method be static? Why or why not?)

  Update your main method to call the above a few times, and print a couple of resuts.
  We find that the built-in toString for arrays is useless (*&^% java!). Instead, print out some spot checks — print four different locations in the array (along with the expected results).

• Write a method sumFromTo, which takes in an array of doubles data and two indices start and stop, and returns the sum of data[start]…data[stop-1]. (Should this method be static? Why or why not?)

  Again, update your main to print a few test results.

• Add my test files to the same directory: Lab12Tester.java, TestUtils.java. Edit Lab12Tester's main and uncomment the calls to the test-method; then compile the files and run Lab12Tester's main.

• For debugging purposes, write a function static String arrayToString(double[]) which returns a string suitable for printing. E.g. something like "{3.2, 7.1, 0, 8.23}" or "[0: 3.2, 1: 7.1, 2: 0, 3: 8.23]".
  Note that getting the output exactly correct means handling one case specially, inside the loop.

  Again, update your main to print a few test results.
  (More properly, add those tests to Lab12Tester#main, and keep Lab12 focused just on the methods which do real work.)

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©2010, Ian Barland, Radford University Last modified 2010.Nov.16 (Tue)

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