初始化方法继承 [英] Init method inheritance

问题描述

如果我有一个带有初始化方法的抽象类A:

If I have abstract class A with an init method:

abstract class A(){
  init {
    println("Hello")
  }     
}

然后是扩展A的B类

class B(): A()

如果我像这样实例化B

If I instantiate B like this

fun main(args: Array<String>){
  B()
}

A中的init方法是否仍然运行并打印Hello?

Does the init method in A still get run and Hello gets printed?

如果没有，我该怎么做才能让A的init方法运行?

And if not, what do I need to do to have the init method of A get run?

推荐答案

是的，初始化派生类实例时，将运行基类的init块.

Yes, an init block of a base class gets run when the derived class instance is initialized.

在Kotlin中，类似于Java，按以下方式构造类的实例:

In Kotlin, similarly to Java, an instance of a class is constructed in the following way:

1. 已分配一个对象.

1. An object is allocated.

该类的构造函数被调用. (a)

The constructor of the class is called. (a)

1. 如果类具有超类，则在执行类构造逻辑之前会调用超类构造函数；
   ^{(即，对超类递归执行(a)点，然后从此处继续执行)}

1. If the class has a superclass, the superclass constructor is called before the class construction logic is executed;
   ^{(i.e., the point (a) is executed recursively for the superclass, then the execution continues from here)}

如果该类具有属性初始化器或init块，则它们将按照它们在类主体中出现的顺序执行；

If the class has property initializers or init blocks, they are executed in the same order as they appear in the class body;

如果构造函数具有主体(即它是辅助构造函数)，然后执行主体.

If the constructor has a body (i.e. it is a secondary constructor) then the body is executed.

在此描述中，您可以看到，在构造B时，在执行B初始化逻辑之前，尤其是在A的所有init块之前，将调用A的构造函数.被执行.

In this description, you can see that, when B is constructed, the constructor of A is called before B initialization logic is executed, and, in particular, all init blocks of A are executed.

^{(此逻辑的可运行演示)}

关于术语的小注释:init块实际上不是单独的方法.相反，所有init块与成员属性初始化程序一起都被编译到构造函数的代码中，因此应将它们视为构造函数的一部分.

A small remark on terminology: init block is not actually a separate method. Instead, all init blocks together with member property initializers are compiled into the code of the constructor, so they should rather be considered a part of the constructor.

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