【翻译】Abstract Classes Have Constructors

最新推荐文章于 2023-11-20 17:21:44 发布

iteye_19040

最新推荐文章于 2023-11-20 17:21:44 发布

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分类专栏： java/corejava 文章标签： Java

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本文探讨了Java中抽象类的构造函数作用及其必要性。解释了即使抽象类不能被实例化，构造函数仍然存在的原因，并通过示例代码展示了这一特性。

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1) In Java , we have default constructors provided for classes by the compiler (in case one is not declared).

2) The abstract classes can't be instantiated by using the new operator because they don't provide full implementation of all the methods.

Then does it make sense to have constructors inside abstract classes. Let us find it using a sample abstract class:


public abstract class Test{
   public abstract void doSomething();
}

The decompiled code for this class will show the truth about constructors in abstract classes in Java


public abstract class Test
{
    public Test()
    {
    }
    public abstract void doSomething();
}

Woha!! that constructor was provided by Java. Why?

The reason is that when a class extends any other class and an instance of the subclass is created then the constructor calls are chained and the super class constructors are invoked. This rule is no exception for abstract class

Moreover, having constructors in a class doesn't necessarily mean that instance of that class will be created using the new operator, but the constructors are intended for writing any initializing code.
总而言之，有构造函数的类不见得就能用new操作符来实例化