Flyweight

İnsan sınıfımız olsun. Bu sınıfın içinde yurttaş oldukları ülkelerin bayraklarının resmini de tutalım. Her resim 1mb boyutuna sahip olsun. 1024 tane nesne oluşturduğumuzda bellekte 1gb’lık alan kaplar. Dünya üzerinde yaklaşık 200 ülke olduğuna göre biz programımızda gereksiz yere aynı şeyin kopyasını oluşturuyoruz ve bunu yapmak için de ağır bir bedel ödüyoruz.

Yapılması gereken şey resimlerle diğer bilgileri farklı yapılara toplamak ve gerektiğinde bunları birleştirip göndermek.

// The flyweight class contains a portion of the state of a
// tree. These fields store values that are unique for each
// particular tree. For instance, you won't find here the tree
// coordinates. But the texture and colors shared between many
// trees are here. Since this data is usually BIG, you'd waste a
// lot of memory by keeping it in each tree object. Instead, we
// can extract texture, color and other repeating data into a
// separate object which lots of individual tree objects can
// reference.
class TreeType is
    field name
    field color
    field texture
    constructor TreeType(name, color, texture) { ... }
    method draw(canvas, x, y) is
        // 1. Create a bitmap of a given type, color & texture.
        // 2. Draw the bitmap on the canvas at X and Y coords.

// Flyweight factory decides whether to re-use existing
// flyweight or to create a new object.
class TreeFactory is
    static field treeTypes: collection of tree types
    static method getTreeType(name, color, texture) is
        type = treeTypes.find(name, color, texture)
        if (type == null)
            type = new TreeType(name, color, texture)
            treeTypes.add(type)
        return type

// The contextual object contains the extrinsic part of the tree
// state. An application can create billions of these since they
// are pretty small: just two integer coordinates and one
// reference field.
class Tree is
    field x,y
    field type: TreeType
    constructor Tree(x, y, type) { ... }
    method draw(canvas) is
        type.draw(canvas, this.x, this.y)

// The Tree and the Forest classes are the flyweight's clients.
// You can merge them if you don't plan to develop the Tree
// class any further.
class Forest is
    field trees: collection of Trees

    method plantTree(x, y, name, color, texture) is
        type = TreeFactory.getTreeType(name, color, texture)
        tree = new Tree(x, y, type)
        trees.add(tree)

    method draw(canvas) is
        foreach (tree in trees) do
            tree.draw(canvas)