Comparing one array to another

[Corbin Blake]

I am trying to sort an array and I am getting a < operator cannot be compared to error when i am trying to compare the positions in the array.

ex.
anArray[i] < anArray[minPos];

i = a position in the array
minPos = the minimum position in that array

Am i using the wrong operator or just using it incorrectly?
How would i do it?

If you need to see my code here it is.

 
/**
 * Sorts an array
 */ 
    public void sort()
{
    for(int i = 0; i < seqArray.length -1; i++)
    {
        int minPos = minimumPosition(i);
        swap(minPos, i);
    }
 
}
/**
 * Finds the smallest element in a tail range of the array
 * @param from the first postion in seqArray to compare
 * @return thr postion of the smallest element in the range
 */
    private int minimumPosition(int from)
    {
        int minPos = from;
        for( int i = from +1; i < seqArray.length; i++)
        if (seqArray[i] < seqArray[minPos]) minPos = i;
      return minPos;
    }
 
    private void swap(int i, int j)
    {
        Sequence temp = seqArray[i];
        seqArray[i] = seqArray[j];
        seqArray[j] = temp;
    }
    public void print(Sequence SeqArray)
    {
        for(int i = 0; i < seqArray.length; i++)
            System.out.println(seqArray[i] + " ");
        System.out.println();
    }
// variables - some are not necessary for the above section of code
public Sequence[] seqArray = new Sequence[20];
public Random rand = new Random();
public Sequence[] space = new Sequence[1];
public Sequence sequence;
public String palindrome;
public String[] ArrayB = new String[10];
public String[] gene ={"A","C","G","T"};
public int d = 0;
public int number = 0;
public int length = 0;
public int concentration = 0;
public int testLength = 0;
public int numSeq = 0;
public String p;
 
}
 

[Ernest Friedman-Hill]

You can't compare objects, including Strings or in this case Sequence objects, using < or any other operator besides == and != . You'll need a comparison function. For example, you might give Sequence a method like

public int compare(Sequence s) {
  return someIntMemberIAmMakingUp - s.someIntMemberIAmMakingUp;
}

Now instead of using "<", you can say

if (seqArray[i].compare(seqArray[minPos]) < 0)

I don't know if this is homework and you're obligated to write your own sort method, but note that the java.util.Arrays class has some lovely static sort() methods to sort arrays of many types. To sort an array of some user-defined type, you need to make that type implement the java.util.Comparable interface which has one method, compareTo(), which looks very much like the above compare() method. Note that String already implements Comparable.

There's actually another alternative to implementing Comparable -- you can instead create another class that implements Comparator and use an instance of that to direct the sorting; this is not any easier.

[Corbin Blake]

I think that i implemented what you suggested correctly, I created a method compareTo that looks like this.

public int compareTo(Sequence s)
{
   return this.charAt(k) - s.charAt(k);
}

I got the syntax from the API, for the compareTo method in java.lang.String,
but i keep getting a "cannot resolve symbol error char(int)" what am i doing wrong?

Appreciate the help

[Ernest Friedman-Hill]

Well, does Sequence have a charAt(int) method? I notice that the method uses charAt(), but the error message says char(). The latter would not be a legal method name, as it's a keyword (the name of a built-in type.)
[ December 08, 2004: Message edited by: Ernest Friedman-Hill ]

[Corbin Blake]

Okay, I came up with a better method to use selection sort but (funny, thing is) i am getting the same error. Ha!Ha!Ha! i am going to need a compareTo method, and i have been trying to write it, hopefully someone can walk me through it.

public class SelectionSorter
{
    public Sequence[] seqArray;
    public int indexWhereFound;
    public Sequence order;
    public int current = 0;
    
    
    /**
     * Constructs a selection sorter
     */
    
    public SelectionSorter(Sequence[] a){
        seqArray = a;
    }
    public void sort(){
         indexWhereFound = 0;
            order = seqArray[current];
        for(int current = 0; current < seqArray.length; current++)
        {
        for(int i = 0; i < seqArray.length -1; i++)
        {
             if(seqArray[i].compareTo(order) < 0)
             {
                 indexWhereFound = i;
                 order = seqArray[i];
                }
           String temp;
           temp = a[current]; //saves value before overwriting
           a[current] = a[indexWhereFound]; //swaps
           a[indexWhereFound] = temp;
 
        }
    }
}
    public void print(Sequence[] a)
    {
        for(int i = 0; i < seqArray.length; i++)
            System.out.print(seqArray[i] + " ");
        System.out.println();
    }
}