Java overloaded method

Question

I have an abstract template method:

class abstract MyTemplate
{
    public void something(Object obj)
    {
        doSomething(obj)

     }

    protected void doSomething(Object obj);

}

class MyImpl extends MyTemplate
{

   protected void doSomething(Object obj)
   {
      System.out.println("i am dealing with generic object");
   }

   protected void doSomething(String str)
   {
      System.out.println("I am dealing with string");
   }
}


public static void main(String[] args)
{
   MyImpl impl = new MyImpl();
   impl.something("abc"); // --> this return "i am dealing with generic object"

}

How can I print “I'm dealing with a string” without using an instance in doSomething (Object obj)?

Thank,

Answer 1

Well, you really can't do it. Java cannot do double dispatch out of the box. The problem is that method call bindings are usually done mostly at compile time.

Here http://en.wikipedia.org/wiki/Double_dispatch

and here

http://www.javaperformancetuning.com/articles/ddispatch2.shtml

Answer 2

Impossible. doSomething (Object obj) in MyImpl is a method that overrides doSomething in MyTemplate.

instanceof-operator doSomething (Object obj) MyImpl. , .

Answer 3

, . , . ( ). :

abstract public class MyTemplate<T> {
    abstract public void doSomething(T t);
}

public class MyTemplateImpl extends MyTemplate<Object> {

    @Override
    public void doSomething(Object o) {
        System.out.println("Dealing with a generic Object");
    }
}

public class MyTemplateImplForStrings extends MyTemplate<String> {
    @Override
    public void doSomething(String s) {
        System.out.println("dealing with a String");
    }
}

, :

MyTemplateImplForStrings template = new MyTemplateImplForStrings();
template.doSomething("hello");  //prints ""dealing with a String"

MyTemplate<String> template = new MyTemplateImplForStrings();
template.doSomething("hello");  //prints ""dealing with a String"

: , String; ClassCastExceptions , .

Answer 4

java , Object, String. .

You can try the visitor template if you control all input classes or use reflection , which is slow / complex and easy to make mistakes.