How better refactor chain of methods that can retu

Question

I have code like:

obj1 = SomeObject.method1();
if (obj1 != null) {
  obj2 = obj1.method2();
  if (obj2 != null) {
     obj3 = obj2.method3();
     if (obj3 != null) {
              ............


     return objN.methodM();

   }
  }
 }
....

I have near 10 steps. It seems very fragile and error prone. Is there a better way to check on null chained methods?

Thanks.

Answer 1

Try to format this way:

obj1 = SomeObject.method1();
if (obj1 != null) {
   obj2 = obj1.method2();
}
if (obj2 != null) {
    obj3 = obj2.method3();
}
if (obj3 != null) {
          ............
}

if (objN != null) {
   return objN.methodM();
}
return null;

Don't forget to initialize all your objs to null.

Answer 2

obj1 = SomeObject.method1();
if (obj1 == null) throw new IllegalArgumentException("...");

obj2 = obj1.method2();
if (obj2 == null) throw new IllegalArgumentException("...");

obj3 = obj2.method3();
if (obj3 == null) throw new IllegalArgumentException("...");

if (objN != null) {
   return objN.methodM();
}

Some more discussion here

Answer 3

More context is necessary to answer this question well.

For example, in some cases I'd advocate breaking out the inner if statements into their own methods, following the "each method should do a single thing, completely and correctly." In this case, calling the method and checking for null is that single thing: if it's null, it returns (or throws, depending on your actual needs). If it isn't, it calls the next method.

Ultimately I suspect this is a design issue, though, the solution to which is unknowable without insight into the problem being solved.

As it stands, this single chunk of code requires deep knowledge of (what I suspect are) multiple responsibilities, meaning in almost all cases, new classes, new patterns, new interfaces, or some combination would be required to make this both clean, and understandable.

Answer 4

We can use Java8 Functional Interface approach.

@FunctionalInterface
public interface ObjectValue<V> {
    V get();
}

static <V> V getObjectValue(ObjectValue<V> objectValue)  {
    try {
        return objectValue.get();
    } catch (NullPointerException npe) {
        return null;
    }
}

Object obj = getObjectValue(() -> objectA.getObjectB().getObjectC().getObjectD());
if(Objects.nonNull(obj)) {
//do the operation
}