java - Check chains of "get" calls for null

Question

Let's say I'd like to perform the following command:

house.getFloor(0).getWall(WEST).getDoor().getDoorknob();

To avoid a NullPointerException, I'd have to do the following if:

if (house != null && house.getFloor(0) && house.getFloor(0).getWall(WEST) != null
  && house.getFloor(0).getWall(WEST).getDoor() != null) ...

Is there a way or an already existing Utils class that does this more elegantly, let's say something like the following?

checkForNull(house.getFloor(0).getWall(WEST).getDoor().getDoorknob());

Answer 1

In case you can't avoid breaking Law of Demeter (LoD) as stated in the chosen answer, and with Java 8 introducing Optional, it would be probably the best practice to handle nulls in chains of gets such as yours.

The Optional type will enable you to pipe multiple map operations (which contain get calls) in a row. Null checks are automatically handled under the hood.

For example, when the objects aren't initialized, no print() will be made and no Exceptions will be thrown. It all we be handled gently under the hood. When objects are initialized, a print will be made.

System.out.println("----- Not Initialized! -----");

Optional.ofNullable(new Outer())
        .map(out -> out.getNested())
        .map(nest -> nest.getInner())
        .map(in -> in.getFoo())
        .ifPresent(foo -> System.out.println("foo: " + foo)); //no print

System.out.println("----- Let's Initialize! -----");

Optional.ofNullable(new OuterInit())
        .map(out -> out.getNestedInit())
        .map(nest -> nest.getInnerInit())
        .map(in -> in.getFoo())
        .ifPresent(foo -> System.out.println("foo: " + foo)); //will print!

class Outer {
    Nested nested;
    Nested getNested() {
        return nested;
    }
}
class Nested {
    Inner inner;
    Inner getInner() {
        return inner;
    }
}
class Inner {
    String foo = "yeah!";
    String getFoo() {
        return foo;
    }
}

class OuterInit {
    NestedInit nested = new NestedInit();
    NestedInit getNestedInit() {
        return nested;
    }
}
class NestedInit {
    InnerInit inner = new InnerInit();
    InnerInit getInnerInit() {
        return inner;
    }
}
class InnerInit {
    String foo = "yeah!";
    String getFoo() {
        return foo;
    }
}

So, with your getters chain it will look like this:

Optional.ofNullable(house)
        .map(house -> house.getFloor(0))
        .map(floorZero -> floorZero.getWall(WEST))
        .map(wallWest -> wallWest.getDoor())
        .map(door -> wallWest.getDoor())

The return of it will be something like Optional<Door> which will allow you much safer work without worrying of null exceptions.