Visitor پترن در جاوا (دیزاین پترن در جاوا)

public interface ItemElement {

     public int accept(ShoppingCartVisitor visitor);

}

public class Book implements ItemElement {



     private int price;

     private String isbnNumber;



     public Book(int cost, String isbn) {

          this.price = cost;

          this.isbnNumber = isbn;

     }



     public int getPrice() {

          return price;

     }



     public String getIsbnNumber() {

          return isbnNumber;

     }



     @Override

     public int accept(ShoppingCartVisitor visitor) {

          return visitor.visit(this);

     }



}

public class Fruit implements ItemElement {



     private int pricePerKg;

     private int weight;

     private String name;



     public Fruit(int priceKg, int wt, String nm) {

          this.pricePerKg = priceKg;

          this.weight = wt;

          this.name = nm;

     }



     public int getPricePerKg() {

          return pricePerKg;

     }



     public int getWeight() {

          return weight;

     }



     public String getName() {

          return this.name;

     }



     @Override

     public int accept(ShoppingCartVisitor visitor) {

          return visitor.visit(this);

     }



}

public interface ShoppingCartVisitor {

     int visit(Book book);



     int visit(Fruit fruit);

}

public class ShoppingCartVisitorImpl implements ShoppingCartVisitor {



     @Override

     public int visit(Book book) {

          int cost = 0;

          // apply 5$ discount if book price is greater than 50

          if (book.getPrice() > 50) {

              cost = book.getPrice() - 5;

          } else

              cost = book.getPrice();

          System.out.println("Book ISBN::" + book.getIsbnNumber() + " cost ="

                   + cost);

          return cost;

     }



     @Override

     public int visit(Fruit fruit) {

          int cost = fruit.getPricePerKg() * fruit.getWeight();

          System.out.println(fruit.getName() + " cost = " + cost);

          return cost;

     }



}

public class ShoppingCartClient {



     public static void main(String[] args) {

          ItemElement[] items = new ItemElement[] { new Book(20, "1234"),

                   new Book(100, "5678"), new Fruit(10, 2, "Banana"),

                   new Fruit(5, 5, "Apple") };



          int total = calculatePrice(items);

          System.out.println("Total Cost = " + total);

     }



     private static int calculatePrice(ItemElement[] items) {

          ShoppingCartVisitor visitor = new ShoppingCartVisitorImpl();

          int sum = 0;

          for (ItemElement item : items) {

              sum = sum + item.accept(visitor);

          }

          return sum;

     }



}