Sorting

Hello,

I'm trying to test the insertionSort, quickSort, and mergeSort but I'm getting compilation errors on parts of my program.  Below are the two methods (I think...) that are giving the errors:
-----------------------------------------------------------

private static void choosePivot(Comparable[] theArray, int first, int last) {

      int pivotIndex;
      int mid = (first + last)/2;
            if (theArray[first] <= theArray[mid]) {
                  if (theArray[mid] <= theArray[last]) {
                       pivotIndex = mid;
                  }
                  else {
                       pivotIndex = (theArray[first] <= theArray[last] ? last:first);
                  }
            }
            else if(theArray[last] <= theArray[mid]) {
                 pivotIndex = mid;
            }
            else {
                 pivotIndex = (theArray[first] <= theArray[last] ? first:last);
                 swap(theArray[first], theArray[pivotIndex]);
            }

}  // end choosePivot

//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//*//

 public void swap(int left, int right) {

         Comparable temp = theArray[left];
         theArray[left] = theArray[right];
         theArray[right] = temp;

 } // end swap()

-----------------------------------------------------

Can someone also explain what 'Comparable' is and what it does... because I get the following compilation errors:

operator <= cannot be applied to java.lang.Comparable,java.lang.Comparable  
                        - and -
swap(int,int) cannot be applied to (java.lang.Comparable,java.lang.Comparable)

----------------------------------------------------

Also, the compiler's complaing that it can't find 'theArray' in my swap method:

cannot resolve symbol: Comparable temp = theArray[left];
                                                                     ^

----------------------------------------------------

If you need the rest of my program, please let me know.  Thanks :)
luna621Asked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Mick BarryJava DeveloperCommented:
Comparable is an interface that defines how to compare objects.
It includes one method:
int compareTo(Object o)
See the javadoc for more details.

in your case to use it, instead of:
 if (theArray[first] <= theArray[mid]) {
you would do:
 if (theArray[first].compareTo(theArray[mid])<=0) {
Mick BarryJava DeveloperCommented:
> cannot resolve symbol: Comparable temp = theArray[left];

You need to pass theArray to your swap() method.

public void swap(int[] theArray, int left, int right) {
luna621Author Commented:
Yay!  It worked for the swap method, but how do I ".compareTo" for these?  Someone told me to write the ? : form, but I don't understand what that is... can you please explain?  
------------------------------------------------------------------------------------
            else {
            pivotIndex = (theArray[first] <= theArray[last] ? last:first);
            }
      }
      else if(theArray[last].compareTo(theArray[mid])<=0) {
            pivotIndex = mid;
      }
      else {
            pivotIndex = (theArray[first] <= theArray[last] ? first:last);
            swap(theArray[first], theArray[pivotIndex]);
      }

-----------------------------------------------------------------------------------

I also get this error:

swap(java.lang.Comparable[],int,int) cannot be applied to (java.lang.Comparable,java.lang.Comparable)

swap(theArray[first], theArray[pivotIndex]);

What does that mean?  Thank you!
CompTIA Cloud+

The CompTIA Cloud+ Basic training course will teach you about cloud concepts and models, data storage, networking, and network infrastructure.

Mick BarryJava DeveloperCommented:
> pivotIndex = (theArray[first] <= theArray[last] ? last:first);

pivotIndex = (theArray[first].compareTo(theArray[last])<=0 ? last : first);

> swap(java.lang.Comparable[],int,int) cannot be applied to (java.lang.Comparable,java.lang.Comparable)

you need to pass the array as you have now added it as a param
you also should be passing the index not the array value

swap(theArray, first pivotIndex);
luna621Author Commented:
Yay!  It worked!  Okay, but now I'm testing the program.  Is there a way I can have random integers and Strings sorted through my program?  Is there a way to time how long it takes?

Here's my main method so far...
---------------------------------------

      public static void main(String args[]){

            long start = System.currentTimeMillis();
            Date startTime = new Date(start);

            System.out.println(startTime.toString());

//-------------------------------------------
// start testing... need to input random
// numbers and integers here.
//-------------------------------------------



            long stop = System.currentTimeMillis();
            Date stopTime = new Date(stop);

            System.out.println(stopTime.toString());


//-------------------------------------------
// find out how much time spent...
//-------------------------------------------

            Date totalTime = (stopTime - startTime);

      } // end main()

-------------------------------------------------

I seem to have a problem with this line:  Date totalTime = (stopTime - startTime);

It's giving me this error:  operator - cannot be applied to java.util.Date,java.util.Date

-------------------------------------------------

I believe this is the compacted version of something...

pivotIndex = (theArray[first] <= theArray[last] ? last:first);

Is there another way to write the above (without the question mark, etc.)?

-------------------------------------------------

Sorry for asking so many questions.  This is like a 3-in-1 question!  To be fair, I increased the points :)

-luna621 =^_^=

Mick BarryJava DeveloperCommented:
> Date totalTime = (stopTime - startTime);

startTime and stopTime are longs, it should be:

long totalTime = (stopTime - startTime);

> pivotIndex = (theArray[first] <= theArray[last] ? last:first);
> Is there another way to write the above (without the question mark, etc.)?

Its called a ternary operator: <condition> ? <value> : <value>
It is equivalent to:

if (theArray[first] <= theArray[last])
{
   pivotIndex = last;
}
else
{
   pivotIndex = first;
}

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
luna621Author Commented:
Is there a way for me to have RANDOM integers read into the different sort methods?  Can I do the same for Strings?  Do I need to import anything (i.e. import java.util.*;)?
Mick BarryJava DeveloperCommented:
java.util.Random can be used for generating Random numbers.
luna621Author Commented:
I want to do something like this in my main to compare the execution times of each sorting method:

- Timings of insertionSort, quickSort, & mergeSort -

 Number of (random) elements: #####

insertionSort execution time in millisecs: #####
     quickSort execution time in millisecs: #####
   mergeSort execution time in millisecs: #####

----------------------------------

How would I make it sort the random ints & Strings?  My insertionSort method is:

public static void insertionSort(Comparable[] theArray, int n) {
...
}

Do I write it like this: insertionSort(???, Math.random());

I don't know what to put for the ??? part.  Because the method calls for a Comparable[] theArray... am I suppose to make an array with random ints?  How do I make that Comparable?
Mick BarryJava DeveloperCommented:
You create your array to sort and then fill it with random numbers using Random.

arr = new Comparable[10];
for (int i=0; i<arr.length; i++)
{
   arr[i] = new Integer(myrandom.nextInt());
}
insertionSort(arr, arr.length);
luna621Author Commented:
I think I got it!  Thank you very much!

-luna621 =^_^=
Mick BarryJava DeveloperCommented:
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Java

From novice to tech pro — start learning today.