Why does my removeDuplicates method only remove the duplicate integer the first time it encounters it?

Question

My method for removing the duplicate numbers works but not if a number appears more than twice. e.g. a list with numbers 1,2,2,3,4,5,6,7,7,7,8,9 when using the method gives the list 1,2,3,4,5,6,7,7,8,9

import java.util.*;
public class final SortAndRemove{
  private SortAndRemove(){
    }
public static void selectionSort(List<Integer> a){
    if(a == null)
        return;
    if (a.size() == 0 || a.size() == 1)
        return;

    int smallest;
    int smallestIndex;
    for (int curIndex = 0; curIndex < a.size(); curIndex++) {

        smallest = a.get(curIndex);
        smallestIndex = curIndex;

        for (int i = curIndex + 1; i < a.size(); i++) {
            if (smallest > a.get(i)) {

                smallest = a.get(i);
                smallestIndex = i;
            }
        }


        if (smallestIndex == curIndex);

        else {
            int temp = a.get(curIndex);
            a.set(curIndex, a.get(smallestIndex));
            a.set(smallestIndex, temp);
        }

    }
}


public static void removeDuplicates(List<Integer> a){
    if(a == null)
        return;
    if (a.size() == 0 || a.size() == 1)
        return;
    for(int curIndex = 0; curIndex <a.size(); curIndex++){
        int num = a.get(curIndex);
            for(int i = curIndex + 1; i < a.size(); i++){
                if(num == a.get(i))
                    a.remove(i);
            }

    }

}

  }

Answer 1

Wikipedia states that a utility class:

is a class that defines a set of methods that perform common, often re-used functions. Most utility classes define these common methods under static (see Static variable) scope.

It's good to give your utility class a private constructor (so that it can never be initialised) i.e.

public class SortAndRemove{
 private SortAndRemove() {
  throw new AssertionError();
 }
 ... // Remainder omitted
}

(This is discussed in Effective Java by Joshua Bloch, by the way)

Answer 2

It's also good to make your utility class final (so no classes can extend from your utility because all methods are static)

public final class SortAndRemove{
 private SortAndRemove() {
  throw new AssertionError();
 }
 ... // Remainder omitted
}