什么是Java上的隐式构造函数 [英] What is Implicit constructors on Java

问题描述

是否必须在Java中调用基类构造函数？
在C ++中是可选的，所以我问这个。

Is it mandatory to call base class constructor in Java? In C++ it was optional, so I am asking this.

当我扩展 ArrayAdapter 得到这个错误：隐式超级构造函数ArrayAdapter< String>（）未定义必须显式调用另一个构造函数

When I extend ArrayAdapter, I get this error: "Implicit super constructor ArrayAdapter<String>() is undefined. Must explicitly invoke another constructor"

那么，调用基础构造函数的目的是什么？当我创建对象时，基类构造函数将调用&

So, what is the purpose of calling base constructor? When I create object base class constructor will call & then it comes to derived right.

推荐答案

如果你不自己调用，那么无参数构造函数会被隐式调用如果该构造函数不存在则无效。调用超级构造函数的原因是，超类通常具有一些在构造之后期望处于的状态，这可能包括不能在子类中设置的私有变量。如果不调用构造函数，它将使对象处于可能无效的状态，这可能导致各种问题。

The no-args constructor is called implicitly if you don't call one yourself, which is invalid if that constructor doesn't exist. The reason it is required to call a super constructor is that the superclass usually has some state it expects to be in after being constructed, which may include private variables that can't be set in a sub-class. If you don't call the constructor, it would leave the object in a probably invalid state, which can cause all kinds of problems.

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