java 为什么允许静态嵌套类对象的实例化？
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Why instantiation of static nested class object is allowed?
提问by Parag Meshram
I have started learning Java language for Android Application developement.
我已经开始学习用于 Android 应用程序开发的 Java 语言。
As per my understanding based on static class, we cannot instantiate object of static class.
根据我基于静态类的理解，我们无法实例化静态类的对象。
But why instantiation of static nested class object is allowed in following situaltion?
但是为什么在以下情况下允许静态嵌套类对象的实例化？
class EnclosingClass
{
//...
class static StaticInnerClass
{
//...
}
}
Why we can create object of inner class if it is marked as static?
如果标记为静态，为什么我们可以创建内部类的对象？
EnclosingClass.StaticInnerClass s = new EnclosingClass.StaticInnerClass()
回答by Jon Skeet
As per my understanding based on static class, we cannot instantiate object of static class.
根据我基于静态类的理解，我们无法实例化静态类的对象。
Your understanding of the meaning of "static class" is incorrect. Basically a "static class" in Javais a nested class which doesn't have an implicit reference to an instance of the containing class. See section 8.5.1 of the JLSfor more information, in particular:
您对“静态类”含义的理解是错误的。Java 中的“静态类”基本上是一个嵌套类，它没有对包含类的实例的隐式引用。有关更多信息，请参阅JLS 的第 8.5.1 节，特别是：
The static keyword may modify the declaration of a member type C within the body of a non-inner class or interface T. Its effect is to declare that C is not an inner class. Just as a static method of T has no current instance of T in its body, C also has no current instance of T, nor does it have any lexically enclosing instances.
static 关键字可以在非内部类或接口 T 的主体内修改成员类型 C 的声明。它的作用是声明 C 不是内部类。正如 T 的静态方法在其主体中没有 T 的当前实例一样，C 也没有 T 的当前实例，也没有任何词法封闭实例。
Perhaps you were thinking of static classes in C#, which are completely different?
也许您正在考虑 C# 中的静态类，它们完全不同？
回答by Alessandro
Why we can create object of inner class if it is marked as static?
如果标记为静态，为什么我们可以创建内部类的对象？
You may need to use a nested classin a staticcontext, for example:
您可能需要nested class在static上下文中使用 a ，例如：
public class Test {
public static void main(String args[]) {
InnerClass innerClass = new InnerClass();
}
class InnerClass {
}
}
In this case, when you try to instantiate the innerClassyou get the error:
在这种情况下，当您尝试实例化时，innerClass您会收到错误消息：
No enclosing instance of type Test is accessible. Must qualify the allocation with an enclosing instance of type Test (e.g. x.new A() where x is an instance of Test).
没有可访问类型 Test 的封闭实例。必须使用 Test 类型的封闭实例来限定分配（例如 xnew A()，其中 x 是 Test 的一个实例）。
To avoid this, you could instantiate an object of type Testand create an instance of innerClassfrom it:
为了避免这种情况，您可以实例化一个类型的对象Test并innerClass从中创建一个实例：
Test test = new Test();
InnerClass innerClass = test.new InnerClass();
or better, declare also the innerClassas static and instantiate it in a static context:
或者更好的是，将 也声明innerClass为静态并在静态上下文中实例化它：
public class Test {
public static void main(String args[]) {
InnerClass innerClass = new InnerClass();
}
static class InnerClass {
}
}
回答by Alex Muni
check it, maybe it can help you Nested Classes
检查它，也许它可以帮助您 嵌套类
