Tuesday, July 7, 2015

Optional class of(), ofNullable(), empty() methods

Optional class of(), ofNullable(), empty() methods

In previous post we saw How to avoid Null Pointer Exception using Optional<T> class and Optional<T> Class Introduction.

This post is extension to previous post where we saw different ways of creating Optional<T> instances. In this post we will take deep dive into the code written in Optional<T> class itself.

First, the constructor.

             private Optional() {
this.value = null;
      }
     
           Constructor is private and it creates empty instance. Generally only one empty instance should exist per VM.

Common Optional<> EMTPY instance

private static final Optional<?> EMPTY = new Optional<>();


Now we will take Optional<T> instance creation methods and explore it.

  • Optional.of(..) method

Optional<String> optional = Optional.of("Monday");

of(..) method definition
      public static <T> Optional<T> of(T value) {
            return new Optional<>(value);
      }

      of(T value) is a static method in Optional<T> class. It returns a new instance of Optional<> with specified non-null value. Remember if the value is null then it will throw NullPointerException.


  • Optional.ofNullable( . . ) method

public static <T> Optional<T> ofNullable(T value) {
return value == null ? empty() : of(value);
}
               
          Unlike of(T value) method this method will not throw NullPointerException. If the value passed is null then it return EMPTY instance. If value is not null then it calls of(..) method and returns instance with specified value.

  • Optional.empty() method

public static<T> Optional<T> empty() {
Optional<T> t = (Optional<T>) EMPTY;
return t;

}
               

           This method just returns the EMPTY instance.

In next posts we will explore different methods of Optional<T> class.


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