Is it possible to get a reference to a Java method to invoke it later?

Question

Is it possible to obtain references to an object's methods? For example, I'd like to have a method that invokes other methods as callbacks. Something like:

public class Whatever
{
  public void myMethod(Method m,Object args[])
  {

  }
}

Is this possible?

EDIT: I meant an object's methods. I take it it's not possible?

Answer 1

Yes, it is possible.

You just have the get the method and invoke it.

Here's some sample code:

$cat InvokeMethod.java  
import java.lang.reflect.Method;
import java.lang.reflect.InvocationTargetException;

public class InvokeMethod {

    public static void invokeMethod( Method m , Object o ,  Object ... args )  
    throws IllegalAccessException, 
           InvocationTargetException {

        m.invoke( o, args );

    }

    public static void main( String [] args ) 
    throws NoSuchMethodException,
           IllegalAccessException,
           InvocationTargetException {

         SomeObject object = new SomeObject();
         Method method = object.getClass().getDeclaredMethod( "someMethod",  String.class );
         invokeMethod( method, object, "World");

    }
}

class SomeObject {
    public void someMethod( String name ){
        System.out.println( "    Hello " + name );
    }
}
$javac InvokeMethod.java 
$java InvokeMethod
Hello World
$

Now the question is, what are you trying to do? perhaps are better ways. But as for your question the answer is YES.

Answer 2

Java 7 will have closures which will let you do this.

Until this is available you have two options

• Hold a reference to an interface with a known method on and call that
• Use reflection to call the method.