Question

The following unexpectedly compiled and ran without a problem:

import info.gridworld.actor.Actor;
import java.util.ArrayList;

public class ChameleonKid extends ChameleonCritter
{
    public ArrayList<Actor> getActors()
    {
        ArrayList<Actor> actors = getGrid().getNeighbors(getLocation());
          ArrayList<Actor> frontBack = new ArrayList<Actor>();
          for(Actor i : actors)
              if(getLocation().getDirectionToward(i.getLocation())==getDirection())
                    frontBack.add(i);
        return frontBack;
    }
}

The method getLocation() in the Actor class returns an instance of Location. And then I call the getDirectionToward() method of the Location class. getLocation().getDirectionToward(i.getLocation()). How does this work? I never imported the Location class. How am I able to work with it and call its methods? If that is how it works, when would I need to import a class? Only if I am instantiating it?

I am using Java 7.

Answer 1

Say you have two methods, one returning foo.Location and the other returning bar.Location (two completely different classes happening to have the same name, but in different packages – completely valid):

foo.Location getFooLocation();
bar.Location getBarLocation();

When you can both of these methods in the same class and chain some methods, you don’t need an import:

if(getFooLocation().onlyInFoo()) {
  //...
}
if(getBarLocation().onlyInBar()) {
  //...
}

It works because the compiler is completely sure which version (from which package) of Location are you using and it knows where onlyInFoo() and onlyInBar are available.

But suppose you need a local variable:

Location location;
// much later
location = getFooLocation();

Now the compiler doesn’t really know Location do you mean, so you must help him either by proceeding class name with package:

foo.Location location;

or by importing that class:

import foo.Location;

You should now ask: what if I want to have local variable of both foo.Location and bar.Location? Well, you can’t import them both, obviously:

//WRONG
import foo.Location;
import bar.Location;

What you can do is again: either don’t import at all and use fully qualified names:

foo.Location location1;
bar.Location location;

…or import just one location:

import foo.Location;

//...
Location location1;     //foo.Location
bar.Location location2;