How do I call a method that has a method as its argument?

Question

Here is a piece of code I have: (what I am trying to do with it is: define a method "renamingrule" in my main class, instantiate a instance of my other class "renamescript" and call its rename method passing as a parameter the "renamingrule" method i've defined in the main class. Everything is well in the RenamScript class, no errors, but i dont know how to call the rename method of the script class from my main class/method. thanks)

public class RenameScript2 {

    ...

    public void rename(Method methodToCall) throws IOException, IllegalAccessException, InvocationTargetException {


    try
    {
        ...

            String command = "cmd /c rename "+_path+"\\"+"\""+next_file+"\" "
                    +"\""+methodToCall.invoke(next_file, next_index)+"\"";
            p = Runtime.getRuntime().exec(command);

    }catch(IOException e1) {} catch(IllegalAccessException IA1) {}  catch(InvocationTargetException IT1) {} ;


    }//end of rename


} //end of class
//=======================================

public class RenameScriptMain2 {

    public static String RenamingRule(String input, int file_row)
    {
        String output = "renamed file "+(file_row+1)+".mp3";
        return output;
    }

    public static void main(String[] args) throws IOException
    {
        RenameScript2 renamer = new RenameScript2();
        renamer.setPath("c:\\users\\roise\\documents\\netbeansprojects\\temp\\files");
        try{
            renamer.rename(RenamingRule);
        }catch(IOException e2) {};

        System.out.println("Done from main()\n\n");

    }
} //end of class

Answer 1

You get hold of the Method object through Class.getMethod method. Something like this:

RenameScript2.class.getMethod("rename", parameters);

---

However, I suggest you consider writing an interface for a class that can perform the renaming, instead of passing a Method .

Such interface could look like

interface RenameAction {
    void performRename();
}

To wrap the script in a RenameAction object you would do something like

RenameAction action = new RenameAction() {
    void performRename() {
        // ...
        String command = "cmd /c rename "+_path+"\\"+"\""+next_file+"\" "...
        p = Runtime.getRuntime().exec(command);
        // ...
    }
};

You would then simply do like this:

public void rename(RenameAction action) {
    action.performRename();
}

Answer 2

Firstly, aioobe is definitely correct, passing a Method object is a little ugly. I'll assume that you're stuck with it!

To get a method, you'll need to usereflection . The below code grabs the method called toString on the class Integer . It then invokes the toString method.

Method method = Integer.class.getMethod("toString");
Object o = method.invoke(new Integer(7));
System.out.println(o);

Static methods don't need to pass the first parameter to method.invoke

Method method = File.class.getMethod("listRoots");
System.out.println(method.invoke(null));

This shows the reason why you shouldn't use it. That string "toString" and "listRoots" are not refactorable. If someone renames a method, then instead of a compile-time error, you'll get a runtime exception thrown (hence the exceptions you'll need to catch, NoSuchMethodException and IllegalAccessException ). It's also much slower to use reflection than to use normal code.

Answer 3

Here is how you should do:

1. Make class RenameScript2 abstract by adding an abstract method public static String RenamingRule(String input, int file_row)
2. Then have your main class RenameScriptMain2 extend above class RenameScript2 and provide implementation of the method RenamingRule() .
3. Now inside main method create instance of the class RenameScriptMain2 and call method RenamingRule()