Check if returned value is not null and if so assign it, in one line, with one method call

Question

Java is littered with statements like:

if(cage.getChicken() != null) {
    dinner = cage.getChicken();
} else {
    dinner = getFreeRangeChicken();
}

Which takes two calls to getChicken() before the returned object can be assigned to dinner.

This could also be written in one line like so:

dinner = cage.getChicken() != null? cage.getChicken() : getFreeRangeChicken();

But alas there are still two calls to getChicken().

Of course we could assign a local variable then use the ternary operator again to assign it if it is not null, but this is two lines and not so pretty:

FutureMeal chicken = cage.getChicken();
dinner = chicken != null? chicken : getFreeRangeChicken();

So is there any way to say:

Variable var = some value if some value is not null OR some other value;

And I guess I'm just talking syntax here, after the code is compiled it probably doesn't make much difference how the code was written in a performance sense.

As this is such common code it'd be great to have a one-liner to write it.

Do any other languages have this feature?

Answer 1

Same principle as Loki's answer but shorter. Just keep in mind that shorter doesn't automatically mean better.

dinner = Optional.ofNullable(cage.getChicken())
  .orElse(getFreerangeChicken());

---

Note: This usage of Optional is explicitly discouraged by the architects of the JDK and the designers of the Optional feature. You are allocating a fresh object and immediately throwing it away every time. But on the other hand it can be quite readable.

Answer 2

Java lacks coalesce operator, so your code with an explicit temporary is your best choice for an assignment with a single call.

You can use the result variable as your temporary, like this:

dinner = ((dinner = cage.getChicken()) != null) ? dinner : getFreeRangeChicken();

This, however, is hard to read.

Answer 3

Since Java 9 you have Objects#requireNonNullElse which does:

public static <T> T requireNonNullElse(T obj, T defaultObj) {
    return (obj != null) ? obj : requireNonNull(defaultObj, "defaultObj");
}

Your code would be

dinner = Objects.requireNonNullElse(cage.getChicken(), getFreeRangeChicken());

Which is 1 line and calls getChicken() only once, so both requirements are satisfied.

Note that the second argument cannot be null as well; this method forces non-nullness of the returned value.

Consider also the alternative Objects#requireNonNullElseGet:

public static <T> T requireNonNullElseGet(T obj, Supplier<? extends T> supplier)

which does not even evaluate the second argument if the first is not null, but does have the overhead of creating a Supplier.

Answer 4

If you don't mind to use commons-lang you can use org.apache.commons.lang3.ObjectUtils#defaultIfNull

Your code would be:

dinner = ObjectUtils.defaultIfNull(cage.getChicken(),getFreeRangeChicken())

Answer 5

Using Java 1.8 you can use Optional

public class Main  {

    public static void main(String[] args) {

        //example call, the methods are just dumb templates, note they are static
        FutureMeal meal = getChicken().orElse(getFreeRangeChicken());

        //another possible way to call this having static methods is
        FutureMeal meal = getChicken().orElseGet(Main::getFreeRangeChicken); //method reference

        //or if you would use a Instance of Main and call getChicken and getFreeRangeChicken
        // as nonstatic methods (assume static would be replaced with public for this)
        Main m = new Main();
        FutureMeal meal = m.getChicken().orElseGet(m::getFreeRangeChicken); //method reference

        //or
        FutureMeal meal = m.getChicken().orElse(m.getFreeRangeChicken()); //method call


    }

    static Optional<FutureMeal> getChicken(){

        //instead of returning null, you would return Optional.empty() 
        //here I just return it to demonstrate
        return Optional.empty();

        //if you would return a valid object the following comment would be the code
        //FutureMeal ret = new FutureMeal(); //your return object
        //return Optional.of(ret);            

    }

    static FutureMeal getFreeRangeChicken(){
        return new FutureMeal();
    }
}

You would implement a logic for getChicken to return either Optional.empty() instead of null, or Optional.of(myReturnObject), where myReturnObject is your chicken.

Then you can call getChicken() and if it would return Optional.empty() the orElse(fallback) would give you whatever the fallback would be, in your case the second method.

Answer 6

Use your own

public static <T> T defaultWhenNull(@Nullable T object, @NonNull T def) {
    return (object == null) ? def : object;
}

Example:

defaultWhenNull(getNullableString(), "");

 

Advantages

• Works if you don't develop in Java8
• Works for android development with support for pre API 24 devices
• Doesn't need an external library

Disadvantages

• Always evaluates the default value (as oposed to cond ? nonNull() : notEvaluated())

  This could be circumvented by passing a Callable instead of a default value, but making it somewhat more complicated and less dynamic (e.g. if performance is an issue).

  By the way, you encounter the same disadvantage when using Optional.orElse() ;-)

Answer 7

dinner = cage.getChicken();
if(dinner == null) dinner = getFreeRangeChicken();

or

if( (dinner = cage.getChicken() ) == null) dinner = getFreeRangeChicken();

Answer 8

You could use

Objects.requireNonNullElseGet(cage.getChicken(), () -> getFreerangeChicken())

even nicer with static import:

import static java.util.Objects.requireNonNullElseGet;

requireNonNullElseGet(cage.getChicken(), () -> getFreerangeChicken())

Answer 9

Alternatively in Java8 you can use Nullable or NotNull Annotations according to your need.

 public class TestingNullable {
        @Nullable
        public Color nullableMethod(){
            //some code here
            return color;
        }

        public void usingNullableMethod(){
            // some code
            Color color = nullableMethod();
            // Introducing assurance of not-null resolves the problem
            if (color != null) {
                color.toString();
            }
        }
    }

---

 public class TestingNullable {
        public void foo(@NotNull Object param){
            //some code here
        }

        ...

        public void callingNotNullMethod() {
            //some code here
            // the parameter value according to the explicit contract
            // cannot be null
            foo(null);
        }
    }

http://mindprod.com/jgloss/atnullable.html