Assignment #3 - Arrays

In a single class called HW3 (filename HW3.java), write the methods described below - each works on an array. You will also write a main method (as described below) to perform tests of your other methods. I've provided a starter file HW3.java, which contains a method printArray for printing out the contents of an integer array and a method inputArray for filling an integer array with user input.

• howMany
• isSymmetric
• reverse
• printMatrix

1. Write a method called howMany that takes in an integer array (1st parameter) and an integer value (2nd parameter), and returns the number of occurrences of the value in the array. For example, if the array list is

    {3, 6, 8, 6, 2, 10, 6, 5, 2, 6, 5, 2, 6}
   

   then the call howMany(list, 6) should return 5 (since the value 6 appears in the array 5 times).

    

2. Write a method called isSymmetric which takes in an array of integers and returns a boolean response. The method should return true if the array is the same backwards as forwards, and false otherwise. (i.e. this is like the idea of a palindrome, but with numbers, not letters -- and checking based on array slots, not on digits).

    

3. Write a method called reverse that takes in an integer array (as a parameter) and returns a new array that is a reversal of the original array. For example, if the following array is sent in:

    {2, 4, 9, 10}
   

   The method should return the array:

    {10, 9, 4, 2}
   

   Note that this method should not change the original array at all.

    

4. Write a method called printMatrix that takes in a two-dimensional array as a parameter and prints out the array in the format given in this example:

    {
       {1, 2, 4, 5},
       {6, 7, 8, 9},
       {10, 11, 12, 13},
       {14, 15, 16, 17}
    }
   

   i.e. it should look like a set of sets, arranged roughly as a table (although the columns do not need to line up -- just one "row" per line). It's a comma-separated set of rows, each row a comma-separated set of elements.

    

5. Write a main method for your class to test your other methods. Your main method should do the following.
   • Prompt the user to input a size (integer)
   • Create an array of the given size (assume valid input)
   • Call the inputArray method to let the user fill the array with values
   • Print out the initial array
   • Call the howMany method on the values 6, 10, and 25, and print messages that state how many times these numbers appear in the array
   • Call the isSymmetric method and based on the result, print a message that indicates whether or not the array is the same backwards as forwards
   • Call the reverse method and print the reversed array. Then print the original array to show that it has not been changed by the method.
   • To test the printMatrix method, simply create the two-dimensional array shown in the example above (in the description of this method) and using your method, print the array. (No need for user input on this test).

Sample Output from main()

Enter array size: 10
Enter array element 0: 4
Enter array element 1: 6
Enter array element 2: 8
Enter array element 3: 10
Enter array element 4: 20
Enter array element 5: 25
Enter array element 6: 10
Enter array element 7: 10
Enter array element 8: 4
Enter array element 9: 6
Initial array:
{4, 6, 8, 10, 20, 25, 10, 10, 4, 6}

The number 6 appears 2 times
The number 10 appears 3 times
The number 25 appears 1 times

The array IS NOT symmetric

The reversed array is: 
{6, 4, 10, 10, 25, 20, 10, 8, 6, 4}
Initial array is:
{4, 6, 8, 10, 20, 25, 10, 10, 4, 6}

Test of two dimensional array:
{
    {1, 2, 4, 5},
    {6, 7, 8, 9},
    {10, 11, 12, 13},
    {14, 15, 16, 17}
}

Compiling

Submitting:

 Main-Class: HW3

 jar cvmf manifest.mf hw3.jar *.class HW3.java

 java -jar hw3.jar