Java：如何在不指定完整类型的情况下指定函数参数的类型

Question

Suppose i have a interface like this,

interface MyIntf{
  void generate();
}

and a method like below

void run(Myintf x) {
  x.generate();
}

I could call run() with an object of a class which implements MyIntf.

but is it possible in Java to declare run without an explicit name for the interface.

ie can i specify run() like this?

void run("Some object which has a method called 'void generate()'" x){
  x.generate();
}

and run() can be called with an object of any class which has a method called

void generate();

Answer 1

You must then use reflection to do what you want. Something like:

void run(Object o) {
    Method m = o.getClass().getMethod("generate", new Class[0]);
    if (m!=null)
        m.invoke(o, new Object[0]);
}

You must also add the necessary try/catch (which I don't know by heart), and I think you can pass null instead of the empty arrays.

Answer 2

No, you cannot do that. This is exactly what interfaces are for :) Unless you don't use reflection..

Answer 3

Java uses "nominative" rather than "structural" typing.

Just because a method has the same name and parameters, doesn't mean it does the same thing (put the camera/gun to you head and shoot). If you need to make a legacy type conform to a particular interface, use an adapter. Avoid reflection.

Answer 4

You mean as if you would do something like this?:

void run(Object x) {
  ((Myintf)x).generate();
}

Answer 5

You could do:

void run(Object x){
    try{
        //use reflection to try and run a generate() method on x
    } catch (Exception e){}
}

but there's no way to enforce that at compile time.

Answer 6

It is not possible to specify "some object which has a method called void generate() " in Java in the way that you have in mind.

In principle you could do this with reflection: you just pass in an Object and at runtime you check if there is a void generate() method that you can call. This means however that you are throwing away the type safety that the compiler provides; I don't recommend using this solution.

public void run(Object obj) throws NoSuchMethodException, IllegalAccessException, InvocationTargetException {
    Method m = obj.getClass().getMethod("generate");
    m.invoke(obj);
}

Answer 7

在Java中执行此操作的唯一方法是使用反射或使用instanceof运算符（不建议这样做），然后将要传递的对象强制转换为正确的类/接口。