Java中是否可以实现动态重载解析？

Question

So I have a class of overloaded methods like this:

class Foo {
    public void test(Object value) {
        ...
    }

    public void test(String value) {
        ...
    }
}

I need to pass a property value of a bean to one of these methods depending on its type, but I don't know the actual property type until the runtime. eg

public void run(Object bean, String propertyName) {
    Foo foo = new Foo();
    foo.test(PropertyUtils.getProperty(bean, propertyName));
}

BTW, PropertyUtils.getProperty() is a helper method that returns a value of the specified property on a bean. PropertyUtils.getProperty() returns an Object, so that test(Object value) will be always called and the actual property type will be ignored.

I can figure out the propery type in the runtime, even if its value is null. Is there such a thing as dynamic casting in Java? If not, is there a way to have an overloaded method with the correct parameter type called?

Answer 1

Overriding is what has dynamic binding in Java. Overloading has static binding, and which function is called is determined at compile time, not at runtime. See this SO question.

Therefore you can't use overloading for run time selection of methods. Suggest you use one of the other OOP design patterns in java, or at least instanceof :

public void dispatch(Object o)
{
   if (o instanceof String)
       handleString((String)o);
   else if (o instanceof File)
       handleFile((File)o);
   else
       handleObject(o);
}

Answer 2

这是访客模式的工作。

Answer 3

Overloaded method resolution happens at compile time in Java. You'll have to do the resolution yourself (a switch, if-then-else ladder or table-lookup), or find a different pattern that can be implemented in Java.

Answer 4

I'm not sure you want an answer to this question. You're interested in setting up a situation where

test((String)x)

does not do the same thing as

test((Object)x)

For x which are String s. This is a Bad Idea™ and will just lead to lots of confusion. Use a different method name if you really want different behavior.

Just make test(Object x) dispatch to test(String x) if x is a String , then you don't need to worry about which test method gets called.