Recitation 17 for CS160

Recitation R17 - Arrays & Debugging with Eclipse
Fall 2013

CS160: Foundations in Programming

The purpose of this lab is to learn how to:

Instantiate arrays
Store data into arrays
Access data from arrays
Become comfortable with arrays

as well as to:

Introduce the Eclipse Java debugger
Learn when and how to use the debugger

Arrays

Write the following program from scratch in the following phases:

Phase 1

Create a new R17 project in Eclipse and an associated class.
Declare a class variable (static) array of integers called arrayIntegers of size 100.
Declare a class variable (static) array of doubles called arrayDoubles of size 100.
Declare a class variable (static) array of strings called arrayStrings of size 100.
Declare a class variable (static) array of characters called arrayChars of size 100.
Add four integer class variables (static) to hold the size of each array, initialized to zero.

Phase 2

Add the following methods, with exactly the signatures shown:

private static void readFile(String inputFile) {} private static int computeSum(int size, int [] iArray) {} private static double computeAverage(int size, double [] dArray) {} private static int computeLength(int size, String [] sArray) {} private static char mostCommon(int size, char [] cArray) {}

Create small arrays for testing the static methods in main, for example:

    int iTest[] = {12, 87, 92, 45, 26};
    double dTest[] = {2.34, 4.45, 6.83, 8.33, 13.2};
    String sTest[] = {"a", "ab", "abc", "abcd", "abcde"};
    char cTest[] = {'h', 'j', 'h', 'j', 'k', 'j'};

Implement and test the static methods by calling them from main and printing the return value.

Phase 3

Call the readFile method from main, passing the first command line argument.
Modify the run configuration to pass in "mixed.txt" as the first parameter.
Save the file mixed.txt into your R17/ folder
In readFile, create a scanner for the file within a try/catch block.
In the try block, write a loop that continues as long as there are tokens in the input file.
For each token:
- If the token is an integer, read it into the next element of the integer array and increment the array size.
- If the token is a double, read it into the next element of the double array and increment the array size.
- If the token is a string with 1 character, read it into the next element of the character array and increment the array size.
- Otherwise read the token, read it into the next element of the string array and increment the array size.
After the loop, close the file.
Within the catch block, print a file read error and exit.

After the try/catch block, print the size of all arrays, as follows:

    arrayIntegers size: 14
    arrayDoubles size: 25
    arrayStrings size: 39
    arrayChars size: 13

If you have read the file correctly, your answer will match exactly.

Phase 4

After the readFile call in main, call each of the static methods with each size and array.
Store the return value in local variables.

Print the results from from the local variables, as follows:

    Sum of integers in iArray: 131103
    Average of doubles in dArray: 4105.597815575479
    Length of strings in sArray: 239
    Most common character in cArray: g

If your code works, your answer will match exactly.