Iterator Pattern

2023-10-18 in Design Patterns

Iterator Pattern에 대해 설명하는 페이지입니다.

Environment

• Programming Language: Java

Index

• Index
• Introduction
• How to Use (Example)
• Comments

Introduction

• a.k.a
  • Cursor
• Purpose
  • Allows for access to the elements of an aggregate object without allowing access to its underlying representation.

  • Provides a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

    An aggregate object is an object that contains other objects for the purpose of grouping those objects as a unit. It’s also called a container or a collection. Examples are linked list and hash table.

• Use When
  • Access to elements is needed without access to the entire representation.
  • Multiple or concurrent traversals of the elements are needed.
  • A uniform interface for traversal is needed.
  • Subtle differences exist between the implementation details of various iterators.

How to Use (Example)

public class MenuItem {
    String name;
    String description;
    boolean vegetarian;
    double price;

    public MenuItem(String name, String description, boolean vegetarian, double price) {
        this.name = name;
        this.description = description;
        this.vegetarian = vegatarian;
        this.price = price;
    }
}

public interface Menu {
    public Iterator createIterator();
}

public class DinerMenu implements Menu {
    MenuItem[] menuItems;

    @Override
    public Iterator createIterator() {
        return new DinerMenuIterator(menuItems);
    }
}

import java.util.Iterator;

public class DinerMenuIterator implements Iterator {
    MenuItem[] items;
    int position;

    public DinerMenuIterator(MenuItem[] items) {
        this.items = items;
        position = 0;
    }

    @Override
    public Object next() {
        MenuItem menuItem = items[position];
        position++;
        return menuItem;
    }

    @Override
    public boolea hasNext() {
        if (position >= items.length)
            return false;
        else
            return true;
    }

    @Override
    public void remove() {
        // code for removing an item and shifting the rest
    }
}

Comments

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