Kotlinby关键字作用及使用介绍

//创建接口
interface Base {
    fun print()
}
//实现此接口的被委托的类
class BaseImp(val x:Int) : Base {
    override fun print() {
 
        println(x)
    }
}
//通过关键字by建立委托类
class Derived (b:Base):Base by b
class Main {
    compaNIOn object{
        @JVMStatic
        fun main(args: Array<String>) {
            var baseImp=BaseImp(100)
            Derived(baseImp).print()  //输出100
        }
    }
}

public final class Derived implements Base {
   // $FF: synthetic field
   private final Base $$delegate_0;
   public Derived(@NotNull Base b) {
      Intrinsics.checkNotNullParameter(b, "b");
      super();
      this.$$delegate_0 = b;
   }
   public void print() {
      this.$$delegate_0.print();
   }
}

//定义包含属性委托的类
class Example {
    var p:String by Delegate()
}
//委托的类
open class Delegate {
    operator fun getValue(thisRef:Any?,property:KProperty<*>):String{
        return "$thisRef,这里委托了${property.name} 属性"
    }
    operator fun setValue(thisRef: Any?,property: KProperty<*>,value:String){
        println("$thisRef 的 ${property.name} 属性赋值为 $value")
    }
}
class Main {
    companion object{
        @JvmStatic
        fun main(args: Array<String>) {
            var e=Example()
            println(e.p) //访问该属性 调用getValue函数
            e.p="rururn" //调用setValue()函数
            println(e.p)
        }
    }
}

class LazyTest {
    companion object{
        val lazyValue:String by lazy {
            println("computed!") //第一次调用输出，第二次调用不执行
            "Hello"
        }
        @JvmStatic
        fun main(args: Array<String>) {
            println(lazyValue)
            println(lazyValue)
        }
    }
}

class Site(val map:Map<String,Any?>) {
    val name:String by map
    val url:String by map
}
class TestMain {
    companion object{
        @JvmStatic
        fun main(args: Array<String>) {
            val site=Site(mapOf(
                "name" to "maozh",
                "url"  to "www.baidu.com"
            ))
            //读取映射值
            println(site.name)
            println(site.url)
        }
    }
}

class Foo{
     var notNullBar:String by Delegates.notNull<String>()
}
foo.notNullBar="bar"
println(foo.notNullBar)