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Commit c3d0a79

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added Flyweight design pattern
1 parent 9a1304f commit c3d0a79

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package design_patterns
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/**
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*
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* Flyweight is a structural design pattern that reduces memory costs by reusing a family of objects
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*
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* and storing mutable state outside the object.
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*
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*/
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class BeautifulGarden {
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// we reuse objects with immutable state, in this example trees
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private val existingTrees = mutableListOf<Tree>()
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// mutable state (coordinates) are stored outside the object
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private val placedTrees = mutableListOf<Triple<Int, Int, Tree>>()
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fun placeTree(name: String, description: String, height: Int, x: Int, y: Int) {
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// check if such a tree already exists reuse it otherwise create a new one
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val tree = existingTrees.find { tree -> tree.name == name && tree.description == description && tree.height == height }
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?: Tree(name, description, height).apply(existingTrees::add)
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placedTrees.add(Triple(x, y, tree))
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}
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fun placedTreesAsString(): String {
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val builder = StringBuilder()
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builder.append("Beautiful Garden:\n")
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placedTrees.forEach { (x, y, tree) ->
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builder.append("name: ${tree.name}, height: ${tree.height}, x: $x, y: $y\n")
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}
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builder.append("-|-|-|-|-|-|-|-|-|-|-")
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return builder.toString()
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}
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data class Tree(
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val name: String,
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val description: String,
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val height: Int
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)
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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 FlyweightTest {
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@Test
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fun test() {
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val garden = BeautifulGarden()
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garden.placeTree("oak", "", 21, 10, 10)
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garden.placeTree("birch", "", 15, 10, 20)
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garden.placeTree("birch", "", 16, 10, 30)
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garden.placeTree("birch", "", 17, 10, 40)
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garden.placeTree("oak", "", 21, 20, 10)
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garden.placeTree("oak", "", 21, 20, 20)
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garden.placeTree("oak", "", 21, 20, 30)
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garden.placeTree("birch", "", 15, 20, 40)
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assertEquals("""
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Beautiful Garden:
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name: oak, height: 21, x: 10, y: 10
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name: birch, height: 15, x: 10, y: 20
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name: birch, height: 16, x: 10, y: 30
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name: birch, height: 17, x: 10, y: 40
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name: oak, height: 21, x: 20, y: 10
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name: oak, height: 21, x: 20, y: 20
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name: oak, height: 21, x: 20, y: 30
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name: birch, height: 15, x: 20, y: 40
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-|-|-|-|-|-|-|-|-|-|-
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""".trimIndent(), garden.placedTreesAsString())
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}
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}

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