CreateASet.java

import java.util.Arrays;
import java.awt.Rectangle;

/**
 * A sample of a ploymorphic method.
 * @author scottm
 *
 */
public class CreateASet {
    
    public static void main(String[] args){
        String[] words = {"A", "B", "B", "D", "C", "A"};
        System.out.println( "original: " + Arrays.toString(words));
        System.out.println( "as a set: " + Arrays.toString(makeSet(words)));
        
        Rectangle[] rectList = {new Rectangle(), new Rectangle(), 
                    new Rectangle(0, 1, 2, 3), new Rectangle(0, 1, 2, 3)};
        System.out.println( "original: " + Arrays.toString(rectList));
        System.out.println( "as a set: " + Arrays.toString(makeSet(rectList)));     
        
        
        Object[] mixed = {"A", "C", "A", "B", new Rectangle(),
                new Rectangle(), "A", new Rectangle(0, 1, 2, 3), "D"};
        System.out.println( "original: " + Arrays.toString(mixed));
        System.out.println( "as a set: " + Arrays.toString(makeSet(mixed))); 
    }
    
    /**
     * An example of polymorphism in action. The method relies
     * on Java's inheritance requirement and polymorhphism to call
     * the correct equals method.
     * @param data != null, no elements of data are null
     * @return a Set (no duplicates) of the elements in data.
     */
    public static Object[] makeSet(Object[] data){
        assert data != null : "Failed precondition makeSet. parameter cannot be null";
        assert noNulls(data) : "Failed precondition makeSet. no elements of parameter can be null";
        Object[] result = new Object[data.length];
        int numUnique = 0;
        boolean found;
        int indexInResult;
        for(int i = 0; i < data.length; i++){
            // maybe should break this out into another method
            indexInResult = 0;
            found = false;
            while(!found && indexInResult < numUnique){
                found = data[i].equals(result[indexInResult]);
                indexInResult++;
            }
            if( ! found ){
                result[numUnique] = data[i];
                numUnique++;
            }
        }
        Object[] result2 = new Object[numUnique];
        System.arraycopy(result, 0, result2, 0, numUnique);
        return result2;
    }
    
    // pre: data != null
    // return true if all elements of data are non null,
    // false otherwise
    private static boolean noNulls(Object[] data){
        assert data != null : "Failed precondition makeSet. parameter cannot be null";
        boolean good = true;
        int i = 0;
        while( good && i < data.length ){
            good = data[i] != null;
            i++;
        }
        return good;        
    }
    
}