Sorting a vector using the selection sort method

Question

I have to write a program that sorts a Vector using the selection sort algorithm. Unfortunately the textbook only has about 2 pages on vectors so needless to say I'm pretty clueless on how to manipulate vectors. However I think I'm on the right path, however I'm stuck on one part as shown in the code below.     
private static void  selectionSort(Vector parts)
      int index;
        int smallestIndex;
        int minIndex;
        int temp = 0;
        for (index = 0; index < parts.size() - 1; index++)
          smallestIndex = index;
          for (minIndex = index + 1; minIndex < parts.size(); minIndex++)
           if (parts.elementAt(minIndex) < parts.elementAt(smallestIndex))  // this is where I'm having trouble
              smallestIndex = minIndex;
            parts.setElementAt(temp, smallestIndex);
            parts.setElementAt(smallestIndex, index);
            parts.setElementAt(index, temp); if (parts.elementAt(minIndex) < parts.elementAt(smallestIndex))
is returning "ProcessParts3.java:51: operator < cannot be applied to java.lang.Object,java.lang.Object"
Here is the full program:
import java.util.*;
import java.io.*;
public class ProcessParts3
     static Vector parts;
     public static void main(String[] args)
          loadVector();
     private static void loadVector()
     try
          Scanner fileIn = new Scanner(new File("productionParts.txt"));
          parts = new Vector();
          String partIn;
          while (fileIn.hasNext())
               partIn = fileIn.nextLine();
                    parts.addElement(partIn.trim());
          selectionSort(parts);
               for (int i = 0; i < parts.size(); i ++)
               System.out.println(parts.elementAt(i));
     catch(Exception e)
          e.printStackTrace();
     private static void  selectionSort(Vector parts) //from this part down I'm responsible for the coding, everything
                                                           // everything above this was written by the teacher
             int index;
        int smallestIndex;
        int minIndex;
        int temp = 0;
        for (index = 0; index < parts.size() - 1; index++)
            smallestIndex = index;
            for (minIndex = index + 1; minIndex < parts.size(); minIndex++)
                if (parts.elementAt(minIndex) < parts.elementAt(smallestIndex))
                    smallestIndex = minIndex;
            parts.setElementAt(temp, smallestIndex);
            parts.setElementAt(smallestIndex, index);
            parts.setElementAt(index, temp);
}Edited by: SammyP on Nov 27, 2009 11:43 AM

Answer 1

SammyP wrote:
I have to write a program that sorts a Vector using the selection sort algorithm...Hmmm.... Your teacher is, in my humble opinion, a bit of a tard.
1. Vector is basically deprecated in favor of newer implementations of the List interface which where introduced in [the collections framework|http://java.sun.com/docs/books/tutorial/collections/index.html] with Java 1.5 (which became generally available back in May 2004, and went end-of-support Oct 2009). ArrayList is very nearly a "drop in" replacement for Vector, and it is much better designed, and is marginally more efficient, mainly because it is not syncronised, which imposes a small but fundamentally pointless overhead when the collection is not being accessed across multiple threads (as is the case in your program).
2. Use generics. That "raw" Vector (a list of Objects) should be a genericised List<String> (a list of Strings)... because it's compile-time-type-safe... mind you that definately complicates the definition of your static sort method, but there's an example in the link... Tip: temp should be of type T (not int).
Note that String implements [Comparable<String>|http://java.sun.com/javase/6/docs/api/java/lang/Comparable.html], so two String's can safely be compared using the compareTo method... In Java the mathematical operators (<, >, &#43;, -, /, &#42;, etc) are only applicable to the primitive types (byte char, int, float, etc)... The Java Gods just chose to muddy the waters (especially for noobs) by "overloading" the &#43; operator for String (and String only) to enable succinct, convenient string-concatenation... which I personally now see as "a little bit of a mistake" on there part.
     private static void  selectionSort(Vector parts)  {
int index, smallestIndex, minIndex, temp = 0;
for (index = 0; index < parts.size() - 1; index++) {
smallestIndex = index;
for (minIndex = index + 1; minIndex < parts.size(); minIndex++) {
if (parts.elementAt(minIndex) < parts.elementAt(smallestIndex)) {
smallestIndex = minIndex;
parts.setElementAt(temp, smallestIndex);
parts.setElementAt(smallestIndex, index);
parts.setElementAt(index, temp);
}3. ALLWAYS use {curly braces}, even when not strictly necessary for correctness, because (a) they help make your code more readable to humans, and also (b) if you leave them out, you will eventually stuff it up when you insert a line in the expectation that it will be part of the if statement (for example) but you forgot to also add the now mandatory curly-braces... This is far-too-common source of bugs in noob-code. Almost all professionals, nearly allways allways use curly braces, most of the time ;-)
4. Variable names should be meaningful, except (IMHO) for loop counters... Ergo: I'd rename index plain old i, and minIndex to plain old j
    for ( int i=0; i<list.size()-1; ++i) {
      int wee = i; // wee is the index of the smallest-known-item in list.
      for ( int j=i+1; j<list.size(); ++j ) {Cheers. Keith.
Edited by: corlettk on 28/11/2009 09:49 ~~ This here fraggin forum markup friggin sucks!