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Commit 50ca620

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added Composite design pattern
1 parent 2460d47 commit 50ca620

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package design_patterns
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/**
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*
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* Composite is a structural design pattern that organizes objects into a tree structure
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*
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* and allows clients to access individual objects and groups of objects in the same way.
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*
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*/
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// all components have a common interface
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abstract class MenuComponent(val title: String) {
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// menus and items can give information about themselves
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abstract fun fetchMenuInformation() : String
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}
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class Menu(title: String) : MenuComponent(title) {
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// menu can contain other menus and items
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private val childMenuComponents = mutableListOf<MenuComponent>()
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// addComponent/removeComponent operations are only available for the menu
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fun addComponent(component: MenuComponent) {
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childMenuComponents.add(component)
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}
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fun removeComponent(component: MenuComponent) {
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childMenuComponents.remove(component)
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}
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override fun fetchMenuInformation(): String {
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val builder = StringBuilder()
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builder.append("Menu: $title")
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childMenuComponents.forEach { component ->
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builder.append("\n")
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builder.append(component.fetchMenuInformation())
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}
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return builder.toString()
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}
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}
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// the simple component that contains no others
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class MenuItem(title: String, private val price: Int) : MenuComponent(title) {
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override fun fetchMenuInformation(): String =
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"""
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title: $title
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price: $price
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-------------
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""".trimIndent()
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}
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package design_patterns
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import org.junit.Test
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import org.junit.Assert.assertEquals
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class CompositeTest {
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@Test
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fun test() {
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val menu = Menu("Delicious Restaurant")
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val pizzasMenu = Menu("Pizzas")
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pizzasMenu.addComponent(MenuItem("Cheese pizza", 10))
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pizzasMenu.addComponent(MenuItem("Pepperoni pizza", 11))
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menu.addComponent(pizzasMenu)
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val cakesMenu = Menu("Cakes")
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cakesMenu.addComponent(MenuItem("Chocolate cake", 13))
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cakesMenu.addComponent(MenuItem("Cheese cake", 13))
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menu.addComponent(cakesMenu)
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assertEquals("""
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Menu: Delicious Restaurant
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Menu: Pizzas
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title: Cheese pizza
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price: 10
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-------------
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title: Pepperoni pizza
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price: 11
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-------------
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Menu: Cakes
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title: Chocolate cake
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price: 13
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-------------
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title: Cheese cake
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price: 13
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-------------
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""".trimIndent(), menu.fetchMenuInformation())
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}
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}

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