有没有办法限制对对象成员的访问仅限于通过组合拥有它的对象？

Question

我真的觉得一定有办法解决这个问题。

想象一下，我有大量对象作为所有者类的组件。我想为其成员提供对该所有者类的客户的轻松访问，因此我将所有这些对象公开。这些对象中的每一个也都有其所有成员公开。但是组件的一个成员不应被其所有者的客户访问，只能由其所有者自己访问：

public class ComponentObject
{
    public int int_field;
    public float float_field;
    public Object object_field;

    public Object public_method1()
    {
        //something;
    }

    public Object public_method2()
    {
        //something;
    }

    public Object restricted_to_owner_only()
    {
        //something;
    }
}

//all clients of Owner should be able to access all the members of its components, except
//restricted_to_owner_only, which only Owner should be able to access
public class Owner
{
    public ComponentObject component1;
    public ComponentObject component2;
    public ComponentObject component3;
    //... lots of others
    public ComponentObject component300;
}

有没有办法做到这一点？请注意，任何包中的任何类都可以拥有ComponentObject，因此在restricted_to_owner_only 处使用包级别的可见性似乎不是一种选择。 ComponentObject 就像一个实用程序类，可以在其他应用程序中重用。

也许有一个注释可以在编译时在一些不错的库中强制执行该注释？

编辑：我忘了说 ComponentObject 是现实生活中的参数化类型，并且 Owner 中的每个字段都被不同地参数化。我试图抽象出细节，以便我们可以专注于设计问题本身，但我抽象的太多了。我将在下面发布与实际问题更相似的内容：

public class ComponentObject<T>
{
    public int int_field;
    public float float_field;
    public T object_field;

    //any method could return T or take T as an argument.
    public T public_method1()
    {
        //something;
    }

    public Object public_method2()
    {
        //something;
    }

    public Object restricted_to_owner_only()
    {
        //something;
    }
}

//all clients of Owner should be able to access all the members of its components, except
//restricted_to_owner_only, which only Owner should be able to access
public class Owner
{
    public ComponentObject<String> component1;
    public ComponentObject<File> component2;
    public ComponentObject<Consumer<Boolean>> component3;
    //... lots of others
    public ComponentObject<Integer> component300;
}

编辑 2（可能是一个解决方案）： 伙计们，受罗密欧与朱丽叶的爱的启发，我写了这个解决方案，你能找出其中的任何错误吗？还是会按我的预期工作？

//add this class
public class OwnershipToken
{
    private static int id_gen = 0;
    public final int id = id_gen++;

    @Override
    public boolean equals(Object obj)
    {
        return (obj instanceof OwnershipToken) && ((OwnershipToken)obj).id == id;
    }

    @Override
    public int hashCode()
    {
        return id;
    }
}

//Then change this in ComponentObject<T>:
public class ComponentObject<T>
{
    //add this field:
    private final OwnershipToken ownershipToken;

    //add this constructor
    public ComponentObject(OwnershipToken onwershipToken)
    {
        this.ownershipToken = ownershipToken;
    }

    //change restricted_to_owner_only signature:
    public Object restricted_to_owner_only(OwnershipToken ownershipToken)
    {
        //add this condition
        if(this.ownershipToken.equals(ownershipToken)
            //something;
    }
}

//finally, Owner gains a field:
public class Owner
{
    private final OwnershipToken ownershipToken = new OwnershipToken();
    //... etc, remainder of the class
}

这会按预期工作吗？

Answer 1

我明白你想要什么，我认为这是不可能的。 但是，仍然有一种方法可以做到！

在所有者类中创建一个 id：

private int id = new Random().nextInt(10000);

在组件对象中：

private id;

public ComponentObject(int id){
    this.id = id;
}

public Object restricted(int id){
    if(this.id != id)
        return null;
    else
        return object;
}

在所有者中：

private ComponentObject<String> string;

public Owner() {
    string = new ComponentObject<>(id);
    string.restricted(id);
    //if the id is right it will return the restricted object, if not i will                
    //return null   

}