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

User · Accepted Answer

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

User · Answer

Use your own  public static  lt T gt  T defaultWhenNull  Nullable T object   NonNull T def        return  object    null    def   object      Example   defaultWhenNull getNullableString            nbsp   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    -

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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 lt FutureMeal gt  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

User · Answer

If you re not on java 1 8 yet and 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

User · Answer

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

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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

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Since Java 9 you have Objects requireNonNullElse which does   public static  lt T gt  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  lt T gt  T requireNonNullElseGet T obj  Supplier lt   extends T gt  supplier    which does not even evaluate the second argument if the first is not null  but does have the overhead of creating a Supplier

User · Answer

dinner   cage getChicken    if dinner    null  dinner   getFreeRangeChicken      or  if   dinner   cage getChicken        null  dinner   getFreeRangeChicken

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

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