How to avoid Nested null check

Question

I want to retrieve the field from API which present inside classes. Yes I know this is against Law of Demeter but I don't have any option.

Example

getClassA().getClassB().getClassC().getClassD().getAccountId();

So to add null check as its bad code smell so I come with below code:

try{
getClassA().getClassB().getClassC().getClassD().getAccountId();
}catch(NullPointerException ex){
 S.O.P("Null Found");
}

or

ClassA a = getClassA();
if(a!=null){
ClassB b = a.getClassB();
So on.....
}

my question is which is best approach the above mentioned one or explicitly retrieve each class and check null and go to next level This is against Law of Demeter

Look here: oracle.com/technetwork/articles/java/… It is exactly explained your problem — aw-think
– aw-think, Commented Feb 27, 2015 at 12:25
I would say that your architecture/design is not right if you have such problem. As you said yourself, you violate Law of Demeter, which could solve this problem. Could you provide a broader context of what you are trying to do? — Jaroslaw Pawlak
– Jaroslaw Pawlak, Commented Feb 27, 2015 at 12:25
@NwDx Optional won't help here, it would be a set of nested isPresent() calls. — Jaroslaw Pawlak
– Jaroslaw Pawlak, Commented Feb 27, 2015 at 12:25
@JaroslawPawlak: Nope, you can call the latest get and only test there. — aw-think
– aw-think, Commented Feb 27, 2015 at 12:26
Even i agree this is very bad design very tight couple. This API i am consuming so cant tell them to provide isPresent() or isEmpty() method on Parent .I dont have any other option. — user2387280
– user2387280, Commented Feb 27, 2015 at 12:53

SMA · Accepted Answer · 2015-02-27 12:27:15Z

2

Null Object design pattern is the way to which is being absorbed in Java 8 via Optional class which means you have a wrapper within which either you have the data or you have empty data.

Its something like

             MyObject
      RealObject    NullObject

Where instead of passing null, you pass NullObject which provides the same interface as MyObject (which can be concrete/abstract/interface class)

answered Feb 27, 2015 at 12:27

SMA

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6 Comments

user2387280 Over a year ago

Thanks @SMA for you input i have checked that before posting here but that is for Java8 right?But i am looking for Java 7

user2387280 Over a year ago

Here I am consuming API so i cant tell them to pass empty nested object.

SMA Over a year ago

Try utilising the same concept as i stated Null Object design pattern. See the class hierarchy that it follows (i just gave a hint above in my answer)

Jaroslaw Pawlak Over a year ago

@user2387280 Your project should be isolated from code that you cannot change. Create your own isolation layer which will expose only the necessary part of third party API you are using. If you are using TDD, this should have integration test.

user2387280 Over a year ago

Do u see any problem in my option 1?I am handlingexception

|

aw-think · Accepted Answer · 2015-03-01 09:36:18Z

This needs Java 8, you are right. I think this will function in a similar way in Guava.

public class OptionalTest {

  public static void main(String[] args) {
    A a = new A();
    Optional<A> opa = Optional.ofNullable(a);
    int accid = opa.map(A::getClassB).map(A.B::getClassC).map(A.B.C::getClassD).map(A.B.C.D::getAccountID).orElse(-1);

    if (accid > -1) {
      System.out.println("The account id is: " + accid);
    } else {
      System.out.println("One of them was null. Please play with commenting.");
    }
  }

    static class A {
      B b = new B();
      //B b = null;
      B getClassB() {
        return b;
      }

      static class B {
        //C c = new C();
        C c = null;
        C getClassC() {
          return c;
        }

          static class C {
            D d = new D();
            //D d = null;
            D getClassD() {
              return d;
            }

              static class D {
                private final int accountId = 2;
                int getAccountID() {
                  return accountId;
                }
              }
          }
      }
    }
}

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