在Java中，导入的类可以与导入的类具有相同的简单名称吗？有什么限制吗？

发布于 2024-11-15 01:16:35 字数 514 浏览 3 评论 0原文

如果我在包 abc 中有一个类名 ClassX，并且我想导入类 abxClassX

Java 中是否有一些限制阻止我这样做？就用法而言，我始终可以使用导入类的完全限定名称，对吗？

Eclipse 似乎无法解决此导入问题，我需要知道 Java 本身是否存在导致问题的限制。

以下代码是否合法：

a\b\c\ClassX.java :

package a.b.c;
public class ClassX {
//
}

a\b\x\ClassX.java :

package a.b.x;

import a.b.c.ClassX;

public class ClassX {
    public static void main(String[] args) {
        a.b.c.ClassX newObj = new a.b.c.ClassX();
    }
}

如果不合法，那么为什么？

原文

If I have a class names ClassX in package a.b.c, and I want to import the class a.b.x.ClassX

Is there some restriction in Java preventing me from doing so? As far as usage goes, I can always use the fully qualified name of the imported class, right?

Eclipse seems to be unable to resolve this import, I need to know if there is a restriction in Java itself that is causing the problem.

Is the following code legal:

a\b\c\ClassX.java :

package a.b.c;
public class ClassX {
//
}

a\b\x\ClassX.java :

package a.b.x;

import a.b.c.ClassX;

public class ClassX {
    public static void main(String[] args) {
        a.b.c.ClassX newObj = new a.b.c.ClassX();
    }
}

If no, then why?

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獨角戲 2024-11-22 01:16:35

更准确地说，

这并不是说我们不允许导入与导入它的类具有相同简单名称的类，
而是不允许我们导入类的名称与已导入的任何类相同。

尝试这样做将导致错误消息：[NameOfImportingClass] 已在此编译单元中定义。

此限制的目的是防止名称歧义/冲突。

例如，如果没有导入，以下所有内容都是合法的：

package a;
class B{}

package b;
class B{
   a.B objectPackageaB; //legal - full-package-name so no ambiguity
   b.B objectPackagebB; //legal - full-package-name so no ambiguity
   B objectB; //legal, as now it can only represent B from package "b" -> b.B 
}

现在让我们添加 import aB

package b;    
import a.B; // <---

class B {
     b.B objectbB;  //still legal, full-package-name so no ambiguity
     a.B objectaB;  //still legal, full-package-name so no ambiguity
     B objectB;   //ambiguous, so ILLEGAL. Which type B should represent? a.B OR b.B?
}

如果 Java 无法阻止这种情况，则需要决定 B objectB 应表示什么类型。

我们有两个选择：

它代表 bB，因此键入导入。但这意味着要使用 a 包中的 B，我们仍然需要将其编写为 aB，这意味着 import aB ; 是冗余/死代码，只会让程序员感到困惑。
它代表aB，因此输入导入。但这会让人感觉不自然，因为在类 B{ } 中，B 会代表一些其他类型！ 。

上述解决方案都不好。

如果没有好的解决方案，最好的选择就是防止问题出现。

To be more precise

it is NOT that we are not allowed to import classes with same simple name as class importing it,
but we are not allowed to name importing class same as any class which is already imported.

Attempting to do so will result in error message: [NameOfImportingClass] is already defined in this compilation unit.

Purpose of this restriction is to prevent name ambiguity/clashes.

For example without imports all below is legal:

package a;
class B{}

package b;
class B{
   a.B objectPackageaB; //legal - full-package-name so no ambiguity
   b.B objectPackagebB; //legal - full-package-name so no ambiguity
   B objectB; //legal, as now it can only represent B from package "b" -> b.B 
}

Now lets add import a.B

package b;    
import a.B; // <---

class B {
     b.B objectbB;  //still legal, full-package-name so no ambiguity
     a.B objectaB;  //still legal, full-package-name so no ambiguity
     B objectB;   //ambiguous, so ILLEGAL. Which type B should represent? a.B OR b.B?
}

IF Java would not prevent such situation, it would need to make decision what type B objectB should represent.

We have two options:

it would represent b.B so type which is importing. But that means to use B from a package we still would need to write it as a.B, which means import a.B; is redundant/dead code which would only be confusing programmers.
it would represent a.B so type which is imported. But that would feel unnatural since inside class B{ }, B would represent some other type!.