public interface Planet {

    public abstract void display(int x, int y);

}

public class Tree implements Planet {

    private int x;

    private int y;

    private String height;

    public int getX() {

        return x;

    }

    public void setX(int x) {

        this.x = x;

    }

    public int getY() {

        return y;

    }

    public void setY(int y) {

        this.y = y;

    }

    public Tree(String height) {

        this.height = height;

    }

    @Override

    public void display(int x, int y) {

        System.out.println(height + "Tree in x=" + x + " y=" + y);

    }

}

public class PlanetFactory {

    private static final HashMap<String, Planet> planetMap = new HashMap<String, Planet>();

    public static Planet getTree(String height) {

        Tree tree = (Tree) planetMap.get(height);

        if(tree == null) {

            tree = new Tree(height);

            planetMap.put(height, tree);

            System.out.println("Creating tree of height : " + height);//只有在map中找不到对象才创建一个，将这句话打印出来

        }

        return tree;

    }

}

public class Client {

    private static final String height[] = {"Tall", "Medium", "Short"};

    private static String getRandomHeight() {

        return height[(int) (Math.random() * height.length)];

    }

    private static int getRandomX() {

        return (int) (Math.random() * );

    }

    private static int getRandomY() {

        return (int) (Math.random() * );

    }

    public static void main(String[] args) {

        for(int i = ; i < ; i++) {

            Tree tree = (Tree) PlanetFactory.getTree(getRandomHeight());

            tree.display(getRandomX(), getRandomY());

        }

    }

}