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interface RecyclerViewAdapter {
    fun getItemCount(): Int
    fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int)
}

class ListAdapter(private val items: List<String>) : RecyclerViewAdapter {

    override fun getItemCount(): Int {
        return items.size
    }

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interface Target {
    fun request()
}

class Adaptee {
    fun specificRequest() {
        // implementation
    }
}

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class DatabaseHelper private constructor(context: Context) {
    companion object {
        private var instance: DatabaseHelper? = null
        fun getInstance(context: Context): DatabaseHelper {
            if (instance == null) {
                instance = DatabaseHelper(context)
            }
            return instance!!
        }
    }

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class Singleton private constructor() {
    companion object {
        private var instance: Singleton? = null
        fun getInstance(): Singleton {
            if (instance == null) {
                instance = Singleton()
            }
            return instance!!
        }
    }

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class Client {
    fun operation(prototype: Prototype) {
        val prototypeClone = prototype.clone()
        // use the clone
    }
}

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class ConcretePrototype : Prototype {
    var attribute: String = ""

    override fun clone(): Prototype {
        val clone = ConcretePrototype()
        clone.attribute = this.attribute
        return clone
    }
}

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interface Prototype {
    fun clone(): Prototype
}

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class User {
    var name: String = ""
    var email: String = ""
    var age: Int = 0
    var address: String = ""

    override fun toString(): String {
        return "User(name='$name', email='$email', age=$age, address='$address')"
    }
}

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class Product {
    var partA: String = ""
    var partB: String = ""
    var partC: String = ""
}

interface Builder {
    fun buildPartA(part: String)
    fun buildPartB(part: String)
    fun buildPartC(part: String)

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interface AlertDialog {
    fun show()
}

class MaterialAlertDialog : AlertDialog {
    override fun show() {
        println("Showing Material Design Alert Dialog")
    }
}