Question

I’ve been looking into Java reflections. This is an example from Wikipedia http://en.wikipedia.org/wiki/Reflection_(computer_programming):

// Without reflection
new Foo().hello();

// With reflection
Class<?> cls = Class.forName("Foo");
cls.getMethod("hello").invoke(cls.newInstance());

I find this a bit counter-intuitive because the method is called before creating an instance.

Reflections of course could be useful to call game leves, especially if there are hundreds of them.

EDIT – SOME SOLUTIONS:

Here is a simple example of reflection which works on Android:

    try {                
        Class<?> clazz = Class.forName("com.test.Foo");                
        clazz.newInstance();            
    } catch (Exception e) {                
        throw new IllegalStateException(e);            
    }

and the class file

public class Foo {

    Foo(){  
        hello();    
    }

    private void hello() {  
        Log.e("FOO", "Hello!");
    }
}

Suppose one wants to call an Activity by reflection:

Activity activity;
try {                
  Class<?> clazz = Class.forName("com.test.MyLevelActivity");                
  activity = (Activity) clazz.newInstance();            
} catch (Exception e) {                
  throw new IllegalStateException(e);            
}
startActivity(new Intent(this,activity.getClass()));

Suppose a level which contains data and methods should be ‘loaded’ by reflection:

    Level currentLevel;
    try {                
        Class<?> clazz = Class.forName("com.test.Level_1_1");                
        currentLevel = (Level) clazz.newInstance();            
    } catch (Exception e) {                
        throw new IllegalStateException(e);            
    }

    String levelName = currentLevel.getLevelName();
    String result = Integer.toString(currentLevel.processData(3, 7));

    Toast.makeText(this, levelName + " result= " + result, Toast.LENGTH_LONG).show();

Here are the classes:

public abstract class Level {

   public abstract String getLevelName();

   public abstract int processData(int a, int b);

}


public class Level_1_1 extends Level{
   private String levelName = "level 1.1";

   public String getLevelName(){
      return levelName;
   }

   public int processData(int a, int b) {
      return a * b;
  }
} 

Answer 1

here

foo.hello();

can’t work, foo is just an object that does not have a method hello().

Things that are unfamiliar may seem counter-intuitive, but eventually new idioms become natural. Just go with the standard approach.

To understand it, consider that the method definition is not part of the object, you write the method once for the class, it “lives” independently of any given object. Hence it’s quite reasonable for the class to say “hey method, apply yourself in the context of this object, he’s one of us”