使类仅可从特定类实例化 [英] make class only instantiable from specific class

问题描述

假设我有3个班级 class1 ， class2 和 class3 .

Let's say I have 3 classes class1, class2 and class3.

如何让 class1 只能由 class2 ( class1 object = new class1())实例化，而不能由class3实例化或其他任何班级?

How can I have it that class1 can only get instantiated by class2 (class1 object = new class1()) but not by class3 or any other class?

我认为它应该与修饰符一起使用，但是我不确定.

I think it should work with modifiers but I am not sure.

推荐答案

我想将您的类重命名为 Friend ， Shy 和 Stranger . Friend 应该可以创建 Shy ，但是 Stranger 应该不能.

I want to rename your classes to Friend, Shy and Stranger. The Friend should be able to create Shy, but Stranger should not be able to.

此代码将编译:

package com.sandbox;

public class Friend {

    public void createShy() {
        Shy shy = new Shy();
    }

    private static class Shy {

    }

}

但是此代码不会:

package com.sandbox;

public class Stranger {

    public void createShy() {
        Friend.Shy shy = new Friend.Shy();
    }

}

此外，如果我们创建一个名为 FriendsChild 的新类，则该不会进行编译:

In addition, if we create a new class called FriendsChild, this won't compile either:

package com.sandbox;

public class FriendsChild extends Friend {

    public void childCreateShy() {
        Shy shy = new Shy();
    }

}

这种命名约定在您考虑时是有意义的.仅仅因为我是某人的朋友，并不意味着我的孩子认识他们.

And this naming convention makes sense when you think about it. Just because I'm a friend of someone doesn't mean my child knows them.

请注意，所有这些类都在同一个程序包中.据我了解，这是您正在寻找的方案.

Notice that all these classes are in the same package. As far as I can understand, this is the scenario you're looking for.

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