Kotlin中协变、逆变和不变 Kotlin中协变、逆变和不变示例详解

// 需要有对比的功能，没有的话就会报错a<b
//加入限制 Comparable 具有对比的功能
fun<T:Comparable<T>> maxOf(a:T,b:T):T{
 return if (a<b) b else a
}

val a=2
val b=3
val maxOf = maxOf(2, 3)
 println("shiming "+maxOf)

 shiming 3

data class Complex(val a:Double,val b:Double):Comparable<Complex>{
 override fun compareTo(other: Complex): Int {
 return (value()-other.value()).toInt()
 }
 fun value():Double{
 return a*a+b*b
 }

 override fun toString(): String {
 return "$a*$a+$b*$b="+(a*a+b*b)
 }
}

 val Complex1=Complex(4.0,5.0)
 val Complex2=Complex(5.0,6.0)
 println("shiming Complex1="+Complex1)
 println("shiming Complex2="+Complex2)
 println("shiming"+Complex1.compareTo(Complex2))

04-16 11:22:10.824 26429-26429/com.kotlin.demo I/System.out: shiming Complex1=4.0*a+5.0*b=41.0
04-16 11:22:10.824 26429-26429/com.kotlin.demo I/System.out: shiming Complex2=5.0*a+6.0*b=61.0
04-16 11:22:10.824 26429-26429/com.kotlin.demo I/System.out: shiming-20

 (1..2).map { println("shiming $it=="+it) }

/**
 * Returns a list containing the results of applying the given [transform] function
 * to each element in the original collection. 
 (1..2).map调用的底层的方法
 */
public inline fun <T, R> Iterable<T>.map(transform: (T) -> R): List<R> {
 return mapTo(ArrayList<R>(collectionSizeOrDefault(10)), transform)
}
/** A function that takes 22 arguments. function中最多的参数22.一共有23个方法 */
public interface Function22<in P1, in P2, in P3, in P4, in P5, in P6, in P7, in P8, in P9, in P10, in P11, in P12, in P13, in P14, in P15, in P16, in P17, in P18, in P19, in P20, in P21, in P22, out R> : Function<R> {
 /** Invokes the function with the specified arguments. */
 public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21, p22: P22): R
}

data class ComplexNumber< T : Number>(val a:T,val b:T){
 override fun toString(): String {
 return "$a*$a+$b*$b"
 }
}

//按照重载的定义这两个方法应该编译的过的，但是Java和kotlin编译完了成了object或者是没有
fun needList(list:List<Double>){
}
fun needList(list:List<Int>){
}

 public static final void needList(@NotNull List list) {
  Intrinsics.checkParameterIsNotNull(list, "list");
 }

 public static final void needList(@NotNull List list) {
  Intrinsics.checkParameterIsNotNull(list, "list");
 }

//inline inline可用内联函数(inline function)消除这些额外内存开销,
//说白了就是在调用处插入函数体代码,以此减少新建函数栈和对象的内存开销!
inline fun<reified T> getT(){
 println("shiming"+T::class.java)
}

getT<String>()
getT<Double>()
//通过反编译得到的结果，说白了，其实就是打印了，这样永远都不会丢失
  String var21 = "shiming" + String.class;
  System.out.println(var21);
  var21 = "shiming" + Double.class;
  System.out.println(var21);

04-16 15:28:59.775 31782-31782/com.kotlin.demo I/System.out: shimingclass java.lang.String
04-16 15:28:59.775 31782-31782/com.kotlin.demo I/System.out: shimingclass java.lang.Double

data class Person(val name:String,val age:Int){
 //重写，得到json字符串
 override fun toString(): String {
  return "{name="+"\""+name+"\","+"age="+age+"}"
 }
}

//例子 通过inline把这个前面的代码植入到后面
// reified让泛型参数具体化，定义在inline中 ，kotlin实现为伪泛型，需要这个关键字植入到调用出才可以
inline fun <reified T> Gson.fromJson(json:String):T=fromJson(json,T::class.java)
//模拟网络请求返回的json数据，得到bean类
 val person=Person("shiming",20)
 println("shiming "+person)
 val toString = person.toString()
 val person1= Gson().fromJson<Person>(toString)
 println("shiming person1"+person1)

//上面一段代码的反编译的结果，和java是一样的，执行的流程
  Person person = new Person("shiming", 20);
  String toString = "shiming " + person;
  System.out.println(toString);
  toString = person.toString();
  Gson $receiver$iv = new Gson();
  Person person1 = (Person)$receiver$iv.fromJson(toString, Person.class);
  String var25 = "shiming person1" + person1;
  System.out.println(var25);

//out 协变 Number 是Int的父类，协变点函数得返回类型
val numberList:List<Number> = listOf<Int>(1,58)
 public interface List<out E> : Collection<E> {
 // Query Operations
 override val size: Int

 override fun isEmpty(): Boolean
 //告诉编译器 我知道，你不要管我知道怎么搞
 override fun contains(element: @UnsafeVariance E): Boolean
 override fun iterator(): Iterator<E>

 // Bulk Operations
 override fun containsAll(elements: Collection<@UnsafeVariance E>): Boolean

 // Positional Access Operations
 /**
  * Returns the element at the specified index in the list.、
  返回值的类型是E
  */
 public operator fun get(index: Int): E

 // Search Operations
 /**
  * Returns the index of the first occurrence of the specified element in the list, or -1 if the specified
  * element is not contained in the list.
  */
 public fun indexOf(element: @UnsafeVariance E): Int

 /**
  * Returns the index of the last occurrence of the specified element in the list, or -1 if the specified
  * element is not contained in the list.
  */
 public fun lastIndexOf(element: @UnsafeVariance E): Int

 // List Iterators
 /**
  * Returns a list iterator over the elements in this list (in proper sequence).
  */
 public fun listIterator(): ListIterator<E>

 /**
  * Returns a list iterator over the elements in this list (in proper sequence), starting at the specified [index].
  */
 public fun listIterator(index: Int): ListIterator<E>

 // View
 /**
  * Returns a view of the portion of this list between the specified [fromIndex] (inclusive) and [toIndex] (exclusive).
  * The returned list is backed by this list, so non-structural changes in the returned list are reflected in this list, and vice-versa.
  *
  * Structural changes in the base list make the behavior of the view undefined.
  */
 public fun subList(fromIndex: Int, toIndex: Int): List<E>
}

  //in 逆变 ，泛型的继承关系相反 逆变点就是函数参数的类型 Any是Int的父类
 val intComparable:Comparable<Int> = object :Comparable<Any>{
      override fun compareTo(other: Any): Int {
        return 0
      }
    }

public interface Comparable<in T> {
  public operator fun compareTo(other: T): Int
}

public interface MutableList<E> : List<E>, MutableCollection<E> {
  override fun add(element: E): Boolean
  override fun remove(element: E): Boolean
  override fun addAll(elements: Collection<E>): Boolean
  public fun addAll(index: Int, elements: Collection<E>): Boolean
  override fun removeAll(elements: Collection<E>): Boolean
  override fun retainAll(elements: Collection<E>): Boolean
  override fun clear(): Unit
  public operator fun set(index: Int, element: E): E
  public fun add(index: Int, element: E): Unit
  public fun removeAt(index: Int): E
  override fun listIterator(): MutableListIterator<E>
  override fun listIterator(index: Int): MutableListIterator<E>
  override fun subList(fromIndex: Int, toIndex: Int): MutableList<E>
}

 //out 协变 Number 是Int的子类，协变点函数得返回类型
    val numberList:List<*> = listOf<Int>(1,58)
    val any = numberList[1] //星投影，去找父类
    //in 逆变 ，泛型的继承关系相反 逆变点就是函数参数的类型
    val intComparable:Comparable<*> = object :Comparable<Any>{
      override fun compareTo(other: Any): Int {
        return 0
      }
    }
    //星投影，去找父类 Nothing
    intComparable.compareTo()

fun <T> hello(){

}
open class Hello<T>{

}
//这样 就可以使用星投影
class Hello33<T>
//这样也可以使用星投影
class Hello2:Hello<Hello<*>>()
class Hello332:Hello<Hello33<*>>()

    //这样也可以使用星投影
 val raw:Raw<*> = Raw.getRaw()
public class Raw<T> {
  @Override
  public String toString() {
    return "老子是Raw";
  }
  public static Raw getRaw(){
    return new Raw();
  }
}

    //不变的话，就根本没有继承关系，没有任何的关系 原因是这样不安全
//    val list1:MutableList<Number> = mutableListOf<Int>(1,5,4)
    list1.add(BigDecimal(1244444444))
//    val list2:MutableList<Int> = mutableListOf<Number>(1,5,4)

    //泛型的实参不要使用星号
//    val numberList11d:List<*> = listOf<*>(1,58)
//
//    hello<*>()
//
//    val hello: Any = Hello<*>()
fun <T> hello(){

}
open class Hello<T>{

}

package com.kotlin.demo.star_demo
import org.jetbrains.annotations.NotNull
import java.lang.reflect.ParameterizedType

/**
 * author： Created by shiming on 2018/4/14 15:08
 * mailbox：lamshiming@sina.com
 */
//Mvp 中的V层 超级接口
interface IView<out P:Ipresenter<IView<P>>>{
  val presenter:P
}
//P层的超级接口
interface Ipresenter<out V:IView<Ipresenter<V>>>{
//  @NotNull
//  IView getView();
  val view:V
}

abstract class BaseView<out P:BasePresenter<BaseView<P>>>:IView<P>{
  override val presenter:P

  init {
    presenter= findPresenterClass().newInstance()
    presenter.view=this
  }

  /**
   * 得到相对于的Class的文件
   */
  private fun findPresenterClass():Class<P>{
    //不知道，使用星投影去接收 相当于 Class thisClass = this.getClass();
    var thisClass:Class<*> = this.javaClass
//    while(true) {
//      Type var10000 = thisClass.getGenericSuperclass();
//      if(!(var10000 instanceof ParameterizedType)) {
//        var10000 = null;
//      }
//      ParameterizedType var5 = (ParameterizedType)var10000;
//      if(var5 != null) {
//        Type[] var6 = var5.getActualTypeArguments();
//        if(var6 != null) {
//          var10000 = (Type)ArraysKt.firstOrNull((Object[])var6);
//          if(var10000 != null) {
//            Type var2 = var10000;
//            if(var2 == null) {
//              throw new TypeCastException("null cannot be cast to non-null type java.lang.Class<P>");
//            }
//
//            return (Class)var2;
//          }
//        }
//      }
//    }
    //以下的代码相当于上面的代码
    while (true){
      (thisClass.genericSuperclass as? ParameterizedType)
          ?.actualTypeArguments
          ?.firstOrNull()
          ?.let {
            return it as Class<P>
          }?.run{
              thisClass=thisClass.superclass ?:throw IllegalAccessException()
            }
          }
    }

  }


abstract class BasePresenter<out V:IView<BasePresenter<V>>>:Ipresenter<V>{
  //lateinit 延迟初始化
  //@UnsafeVariance 告诉编译器 我很安全 不要管我
  override lateinit var view:@UnsafeVariance V
}

class MainView:BaseView<MainPresenter>()

class MainPresenter:BasePresenter<MainView>()

class Mvp{
  init {
    MainView().presenter.let(::println)
    //相当于下面的代码
//    BasePresenter var1 = (new MainView()).getPresenter();
//    System.out.println(var1);
    MainView().presenter.let { println("shiming P="+it) }
    //相当于下面的代码
//    var1 = (new MainView()).getPresenter();
//    MainPresenter it = (MainPresenter)var1;
//    String var3 = "shiming P=" + it;
//    System.out.println(var3);
//    (new MainPresenter()).getView();

  }
}