README.md

Optional

Optional is a generic class defined in the java.util package that got introduced in Java8.

It facilitates the handling of potentially absent values in a more concise and expressive manner.
It provides a container-like structure to wrap objects, indicating the possibility of a value being present or absent.

Its primary purpose is to provide a safer alternative to handling null values, thereby reducing the risk of NullPointerExceptions. By explicitly acknowledging the possibility of an absent value, Optional encourages developers to write more robust and error-resistant code.

Creating Optional Instances:

To create an Optional instance, following methods are porvided :

1. Optional.of(T value):

   • Creates an Optional object containing a non-null value.
   • Throws: NullPointerException if the value provided is null.
   • Example:

     String name = "John Doe";
     Optional<String> optionalName = Optional.of(name);
     System.out.println("Optional Name: " + optionalName);

     Output:

     Optional Name: Optional[John Doe]

2. Optional.ofNullable(T value):

   • Creates an Optional object containing the specified value.
   • The value can be null, in that case the Optional will be empty.
   • Example:

     String city = null;
     Optional<String> optionalCity = Optional.ofNullable(city);
     System.out.println("Optional City: " + optionalCity);

     Output:

     Optional City: Optional.empty

3. Optional.empty():

   • Creates an empty Optional object with no value/null value.
   • Example:

     Optional<String> optionalEmail = Optional.empty();
     System.out.println("Empty Optional Email: " + optionalEmail);

     Output:

     Empty Optional Email: Optional.empty

Methods and Usage:

using the Optional instance, following methods can be utilized to manipulate and retrieve values.

1. boolean isPresent():

   • Returns true if the Optional contains a non-null value, false otherwise.
   • Example:

     Optional<String> optionalName = Optional.of("John Doe");
     if (optionalName.isPresent()) {
        System.out.println("Name: " + optionalName.get());
     } else {
        System.out.println("No name found.");
     }

     Output:

     Name: John Doe

2. T get():

   • Returns the value wrapped by the Optional if present.
   • Throws: NoSuchElementException if the Optional is empty.
   • Example:

     Optional<String> optionalName = Optional.of("John Doe");
     String name = optionalName.get();
     System.out.println("Name: " + name);

     Output:

     Name: John Doe

3. T orElse(T defaultValue):

   • Returns the value wrapped by the Optional if present.
   • Returns: defaultValue if the Optional is empty.
   • Example:

     Optional<String> optionalCity = Optional.empty();
     String city = optionalCity.orElse("Unknown City");
     System.out.println("City: " + city);

     Output:

     City: Unknown City

4. T orElseGet(Supplier<? extends T> supplier):

   • Returns the value wrapped by the Optional if present.
   • Invokes the supplier function to provide an alternative value if the Optional is empty.
   • Example:

     Optional<String> optionalEmail = Optional.empty();
     String email = optionalEmail.orElseGet(() -> generateDefaultEmail());
     System.out.println("Email: " + email);
     ...
     public String generateDefaultEmail(){ return "abc@def.com"; }

     Output:

     Email: abc@def.com

5. T orElseThrow(Supplier<? extends X> exceptionSupplier):

   • Returns the value wrapped by the Optional if present.
   • Throws an exception produced by the exceptionSupplier if the Optional is empty.
   • Example:

     Optional<String> optionalName = Optional.empty();
     String name = optionalName.orElseThrow(() -> new IllegalArgumentException("Name is absent"));

     Output:

     Exception in thread "main" java.lang.IllegalArgumentException: Name is absent
     .....
     .....

6. void ifPresent(Consumer<? super T> consumer):

• Executes the specified consumer function with the value wrapped by the Optional if present.
• Example:

  Optional<String> optionalPhone = Optional.of("123456789");
  optionalPhone.ifPresent(phone -> System.out.println("Phone: " + phone));

  Output:

  Phone: 123456789

Conclusion:

Optional in Java is a valuable tool for handling potentially absent values without relying on null references and null checks.

without optional (custom null check):

public String getStudentName() {
  Student student = fetchStudent(); // can be null or non-null value
  if(student != null){
    return student.getName();
  }else {
    return null;
  }
}

with optional:

public Optional<String> getStudentName() {
  Optional<Student> student = Optional.ofNullable(fetchStudent()); // can be null or non-null value
  if(student.isPresent()){
    return Optional.of(student.getName());
  }
  return Optional.empty();
}

Note:
when the value wrapped by an Optional is null, it is equivalent to using Optional.empty(). Both represent an empty Optional object with no value.

For example:

String value = null;

Optional<String> optional1 = Optional.ofNullable(value);
Optional<String> optional2 = Optional.empty();

System.out.println(optional1.equals(optional2));  // Output: true

Both Optional.empty() and Optional.ofNullable(null) are commonly used to handle cases where a value might be absent or null. They allow for more explicit and concise handling of null values, reducing the chances of NullPointerExceptions and making the code more readable and robust.