Java 8 Optional: Handling Nulls Properly

Java 8 introduced the Optionalclass to make handling of nulls less error-prone. For example, the following program to pick the lucky name has a null check as:

public static final List<String> NAMES = Arrays.asList("Rita", "Gita", "Nita", "Ritesh", "Nitesh", "Ganesh", "Yogen", "Prateema");

public String pickLuckyNameOldWay(final List<String> names, final String startingLetter) {
  String luckyName = null;
  for (String name : names) {
    if (name.startsWith(startingLetter)) {
      luckyName = name;
      break;
    }
  }
  return luckyName != null ? luckyName : "No lucky name found";
}

This null check can be replaced with the Optional  class method isPresent()  as shown below:

public String pickLuckyNameWIsPresent(final List<String> names, final String startingLetter) {
   final Optional<String> luckyName = names.stream().filter(name -> name.startsWith(startingLetter)).findFirst();

   return luckyName.isPresent() ? luckyName.get() : "No lucky name found";
}

However, notice the writing is no easier than:

return luckyName != null ? luckyName : "No lucky name found";

The Optional  class, however, supports other techniques that are superior to checking nulls. The above code can be re-written as below with  orElse()  method as below:

public String pickLuckyNameWOrElse(final List<String> names, final String startingLetter) {    
  final Optional<String> luckyName = names.stream().filter(name -> name.startsWith(startingLetter)).findFirst();    

  return luckyName.orElse("No lucky name found");
}

The method orElse()  is invoked with the condition "If X is null, populate X. Return X.", so that the default value can be set if the optional value is not present.

There is another method called the ifPresent(Function). You can use this method to invoke an action and skip the null case completely. For example, the program below prints a message in the case, if the condition is met as:

public static void pickLuckyNameOldWay(final List<String> names, final String startingLetter) {    
  String luckyName = null;    
  for (String name : names) {        
    if (name.startsWith(startingLetter)) {            
      luckyName = name;            
      break;        
    }    
  }    
  if (luckyName != null) {        
    postMessage(luckyName);    
  }
}
public static void postMessage(final String winnerName) {    
  System.out.println(String.format("Congratulations, %s!", winnerName));
}

This can be re-written with ifPresent() , as shown below. in a more intuitive manner, as:

public static void pickLuckyNameNewWay(final List<String> names, final String startingLetter) {
   final Optional<String> luckyName = names.stream().filter(name -> name.startsWith(startingLetter)).findFirst();
   luckyName.ifPresent(OptionalIfPresent::postMessage);
}

If we want to throw an exception in case if no name is found, then it would be something like this:

public String pickLuckyNameOldWay(final List<String> names, final String startingLetter) {    
  String luckyName = null;
  // ... same code here
  if (luckyName == null) {        
    throw new NotFoundException("There is no name starting with letter.");    
  }    
  return luckyName;
}

It can be meaningfully replaced with orElseThrow as:

public String pickLuckyNameWOrElse(final List<String> names, final String startingLetter) {    
  final Optional<String> luckyName = names.stream().filter(name -> name.startsWith(startingLetter)).findFirst();    
  return luckyName.orElseThrow(() -> new NotFoundException("There is no name starting with letter."));
}

There are other many more methods in the Optional  class to handle null  in more proper way. You can go through the Optional in Java 8 cheat sheet.

As always, if you want to look into the source code for the example presented above, they are available on GitHub.