基于参数的新类实例 [英] New instance of class based on argument

问题描述

我正在尝试创建一个函数，它接受扩展 Foo 的许多类中的一个，并在其Class中返回该对象的新实例，而不是新实例 Foo 。

I'm trying to make a function that takes one of many classes that extends Foo, and return a new instance of that object in its Class, not a new instance of Foo.

我确定这是一个常见问题。那里有什么好的例子吗？

I'm sure this is a common issue. Is there any good examples out there?

我从未使用过类作为输入参数，只使用类的成员。基于我搜索过的内容，应该可以这样做吗？

I have never used a class as an input parameter, only members of a class. Based on what I have searched for, this should be possible to do?

推荐答案

你传递的是类对象作为参数，或者在 Foo 的子类的实例中？

Are you passing a Class object as the parameter, or in instance of a subclass of Foo?

在任何一种情况下解决方案几乎相同，你使用 newInstance 方法。

The solution is almost the same in either case, you use the newInstance method on the Class object.

/**
 * Return a new subclass of the Foo class.
 */
public Foo fooFactory(Class<? extends Foo> c)
{
    Foo instance = null;
    try {
        instance = c.newInstance();
    }
    catch (InstantiationException e) {
        // ...
    }
    catch (IllegalAccessException e) {
        // ...
    }
    return instance; // which might be null if exception occurred,
                     // or you might want to throw your own exception
}

如果你需要构造函数args，你可以使用Class getConstructor 方法，从那里构造函数 newInstance（...）方法。

If you need constructor args you can use the Class getConstructor method and from there the Constructor newInstance(...) method.

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