see below methods:

- public void plantFlowers( int n )

- public void spinFlowers( )
  * with old style loop
  
- public void spinFlowers( )
  * with new style loop

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package cs1.ParkApp;

import cs1.app.*;
import java.util.ArrayList;

public class Park
{
    // the features (data members)
    
    private ArrayList<Balloon> balloonsList;
    private ArrayList<Flower> flowersList;
    
    // the constructor(s)
    
    public Park()
    {
        // create empty collections of balloons and flowers
        balloonsList = new ArrayList<Balloon>();
        flowersList = new ArrayList<Flower>();
    }
    
    // the behaviors (methods)
    
    public void plantFlowers( int n )
    {
        for (int count = 1; count <= n; count = count + 1)
        {
            String color = canvas.getRandomColor( );
            Flower flower = new Flower( color );       // make a flower
            
            flowersList.add( flower );                 // put the flower in the list
        }
    }

    public void add( Balloon balloon )
    {
        balloonsList.add( balloon );
    }
    
    public void animate( int frames )
    {
        for (int count = 1; count <= steps; count = count + 1)
        {
            canvas.clear();
            
            driftBalloons();    // make all ballons drift a bit
            spinFlowers();      // make all flowers spin a bit
            
            canvas.sleep( 0.1 );
        }
    }

    public void driftBalloons( )
    {
        // go through all balloons one index at a time
        for (int index = 0; index < balloonsList.size(); index = index + 1)
        {
            Balloon balloon = balloonsList.get(index);   // get current balloon

            double dx = canvas.getRandomDouble(-3, 3);   // pick 2 random values
            double dy = -1;
            
            balloon.drift( dx, dy );         // ask balloon to drift a bit
            balloon.draw();                  // ask balloon to draw itself
        }
    }

    // version with enhanced for-loop
    public void driftBalloons( )
    {
        // go through all balloons directly, without index
        for ( Balloon balloon : balloonsList )           // get current balloon automatically
        {
            double dx = canvas.getRandomDouble(-3, 3);   // pick 2 random values
            double dy = -1;
            
            balloon.drift( dx, dy );         // ask balloon to drift a bit
            balloon.draw();                  // ask balloon to draw itself
        }
    }

    // version with regular (index-based) for-loop
    public void spinFlowers( )
    {
        // go through all flowers one index at a time
        for ( int i = 0 ; i < flowersList.size() ; i++ )
        {
            Flower flower = flowersList.get( i );        // get current flower

            flower.spin( );         // ask flower to spin
            flower.draw();          // ask flower to draw itself
        }
    }

    // version with enhanced for-loop
    public void spinFlowers( )
    {
        // go through all flowers directly, without index
        for ( Flower flower : flowersList )           // get current flower automatically
        {
            flower.spin( );         // ask flower to spin
            flower.draw();          // ask flower to draw itself
        }
    }
}