在构造函数中实例化对象 [英] Instantiating object in a constructor

问题描述

以下代码的结果似乎相同，所以我应该何时使用？

It seems that the result of the following code is the same, so when should I use each?

public class Person {
   public Person() {
       this.family = new Family();
   }
   Family family;
}

到

public class Person {
   Family family = new Family();
}

（我能想到的一个场景是，当我有多个构造函数时，我们想要仅在其中一个内部创建一个家庭实例...是唯一的情况吗？）

(one scenario I can think of, is when having multiple constructors and we want to create an instance of family only inside one of them... is that the only case?)

推荐答案

对于类变量 [静态变量]你不能使用第一个，因为你希望初始化只发生一次，而不是每次你调用你的构造函数。

For class variables [static variable] you cannot use the first, since you want the initializtion to happen only once, and not with every time you invoke your constructor.

例如变量，第二个只是第一个的合成糖。

有时你可能必须使用第二个 - for参数构造函数，它们本身 - 传递给你的构造函数。

For instance variables, the second is just a syntatic sugar of the first.
Sometimes you might have to use the second - for argument constructor, which are themselves - passed to your constructor.

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