说明：kotlin构造方法和java稍有不同，许多初学者并不知道怎么实现kotlin构造方法

主函数：

fun main(){
     val bird = Bird5(100.5,78,"yellow")


    bird.printSex();
    println("main: ${bird.age},${bird.weight},${bird.color}")


}

构造方法类：kotlin可以直接在类接变量，然后在init里面赋值，自定义方法就直接写就可以了，然后在主函数里面调用，

class Bird5 (weight : Double = 0.00,age : Int = 1,color : String = "blue"){

    val weight : Double
    val age : Int
    val color : String
    var sex : String = ""

    //构造方法
    init {
        this.weight = weight;
        this.age = age*2

        println("${this.weight}")
        println("${this.age}")
    }

    init{
        this.color = color;
        println("${this.color}")
    }

    //自定义方法
    fun printSex(){
        this.sex = if (this.color == "yellow") "male" else "female"
        println("${this.sex}")
    }

}

运行结果：

100.5
156
yellow
male
main: 156,100.5,yellow

Process finished with exit code 0

end