8.5 The Optional<T> Class & Null Safety

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Introduced in Java 8, java.util.Optional<T> is a single-value container designed to explicitly represent the presence or absence of a value without resorting to error-prone null references.

What is Optional Class?

A value that may or may not be present.

It helps reduce situations where you get NullPointerException because a value is null.

Without Optional

String name = user.getName();

if (name != null) {
    System.out.println(name);
}

With Optional

Optional<String> name = Optional.ofNullable(user.getName());

name.ifPresent(System.out::println);

Think of Optional as a box that may contain a value or may be empty.

Creating Optional Instances

`Optional.of()`

Use when you are sure the value is not null.

// 1. Definite non-null value (throws NPE immediately if value is null)
Optional<String> opt1 = Optional.of("CodeWithSarvy");

If you pass null. It throws NullPointerException.

`Optional.ofNullable()`

Use when the value may be null.

// 2. Value may or may not be null
Optional<String> opt2 = Optional.ofNullable(fetchNullableUsername());

If name is null, you get an empty Optional, not an exception.

of()          → value must NOT be null
ofNullable()  → value MAY be null

`Optional.empty()`

Creates an empty Optional.

// 3. Explicit empty container
Optional<String> opt3 = Optional.empty();

Optional class method

Method	Description
`isPresent()`	Returns `true` if there is a value present, otherwise `false`.
`isEmpty()`	Returns `true` if the `Optional` is empty, otherwise `false`. (Introduced in Java 11)
`ifPresent(Consumer<? super T> action)`	If a value is present, performs the given action with the value, otherwise does nothing.
`ifPresentOrElse(Consumer<? super T> action, Runnable emptyAction)`	If a value is present, performs the given action; otherwise, performs the empty-based action. (Introduced in Java 9)
`get()`	If a value is present, returns the value, otherwise throws `NoSuchElementException`. (Note: Using this without checking is generally discouraged).
`orElse(T other)`	Returns the value if present, otherwise returns the specified `other` default value.
`orElseGet(Supplier<? extends T> supplier)`	Returns the value if present, otherwise invokes the `supplier` and returns the result of that invocation.
`orElseThrow()`	Returns the contained value if present, otherwise throws `NoSuchElementException`. (Introduced in Java 10)
`orElseThrow(Supplier<? extends X> exceptionSupplier)`	Returns the contained value if present, otherwise throws an exception created by the provided supplier.
`filter(Predicate<? super T> predicate)`	If a value is present and matches the predicate, returns an `Optional` describing the value, otherwise returns an empty `Optional`.
`map(Function<? super T, ? extends U> mapper)`	If a value is present, applies the mapping function to it, and returns an `Optional` describing the result if non-null.
`flatMap(Function<? super T, ? extends Optional<? extends U>> mapper)`	If a value is present, applies the mapping function to it (which returns an `Optional`), and returns that `Optional` directly.
`or(Supplier<? extends Optional<? extends T>> supplier)`	If a value is present, returns the `Optional`; otherwise, returns an `Optional` produced by the supplying function. (Introduced in Java 9)
`stream()`	If a value is present, returns a sequential `Stream` containing only that value, otherwise returns an empty `Stream`. (Introduced in Java 9)
`equals(Object obj)`	Indicates whether some other object is "equal to" this `Optional`.
`hashCode()`	Returns the hash code value of the present value, or `0` if no value is present.
`toString()`	Returns a non-empty string representation of this `Optional` suitable for debugging.

What is Optional Class?​

Creating Optional Instances​

Optional.of()​

Optional.ofNullable()​

Optional.empty()​

Optional class method​