泛型

泛型概念和java中的泛型是一致的，没有特别的地方

定义

这里包含有定义和使用，和java中的泛型是一样的想法

fun BaseMain() {
    Table<String>("NieBin")

}

class Table<TYPE> constructor(t: TYPE) {
    init {
        println("This is $t")
    }
}

可转变

这和

fun BaseMain() {
    var dog = Dog("Black")
    var cat = Cat("小黄")
    var animal: Animal = dog
    println("The name is ${animal.name}")
    animal = cat
    println("This name is ${animal.name}")
}


class Table<TYPE> constructor(t: TYPE) {
    init {
        println("This is $t")
    }
}

open class Animal(name: String) {
    var name = "";

    init {
        this.name = name
    }


}

class Dog(name: String) : Animal(name) {
}

class Cat(name: String) : Animal(name) {

}

协变

在java中 String 是Object的子类，但是List<String>是不能转换为List<Object>的，但是在kotlin中却可以这样，如果一个类是另外一个类的子类，那么就可以像普通子类父类之间进行转换赋值了，如下

fun BaseMain() {
    var dogs: List<Dog> = listOf(Dog("A"), Dog("B"))
    var animals: List<Animal> = dogs
    for (animal in animals) {
        println("This animal's name is ${animal.name}")
    }

}

open class Animal(name: String) {
    var name = "";

    init {
        this.name = name
    }


}

class Dog(name: String) : Animal(name) {
}

class Cat(name: String) : Animal(name) {

}

就像普通类一样，是不是很爽

逆向转变

在泛型中，就是可以将父类型转换为子类型的操作

fun BaseMain() {


    val animal: Compare<Animal> = object : Compare<Animal> {
        override fun compare(t: Animal) {
            println("This is animal compare and name is ${t.name}")
        }
    }
    val dogCompare: Compare<Dog> = animal
    dogCompare.compare(Dog("This is black."))
}

open class Animal(name: String) {
    var name = "";

    init {
        this.name = name
    }
}

class Dog(name: String) : Animal(name) {
}

interface Compare<in T> {
    fun compare(t: T)
}

参考文章 讲得特别清晰明白