Class OptionalExamples

java.lang.Object

net.jrodolfo.java_evolution.java08.OptionalExamples

public class OptionalExamples
extends Object

Demonstrates Optional, introduced in Java 8 as a container for values that may be absent.

Before Java 8, many methods returned null when a value could not be found. That made absence invisible in the method signature, so callers had to remember defensive checks and failures often appeared later as NullPointerExceptions.

Optional solves part of that problem by making absence explicit in a return type. A method returning Optional<String> communicates that a value may be missing and encourages the caller to handle that case with operations such as map, filter, orElseGet, and orElseThrow. It is most useful as a return type, not as a replacement for every nullable field or parameter.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	OptionalExamples.User	Small Java 8-style data class used by the Optional examples.

Constructor Summary

Constructors

Constructor	Description
OptionalExamples()

Method Summary

Modifier and Type	Method	Description
String	displayEmail(OptionalExamples.User user)	Uses Optional.orElse(Object) to provide a default value.
String	displayEmailGeneratedLazily(OptionalExamples.User user)	Uses Optional.orElseGet(java.util.function.Supplier) to create a fallback only when the Optional is empty.
Optional<String>	findCompanyDomain(OptionalExamples.User user)	Uses Optional.flatMap(java.util.function.Function) when the transformation already returns an Optional.
Optional<String>	findEmail(OptionalExamples.User user)	Wraps a possibly null user email in an Optional.
Optional<String>	normalizeEmail(OptionalExamples.User user)	Transforms and validates a value while it is inside an Optional.
String	requireEmail(OptionalExamples.User user)	Uses Optional.orElseThrow(java.util.function.Supplier) when the missing value should be treated as an error.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

OptionalExamples

public OptionalExamples()

Method Details

findEmail

public Optional<String> findEmail(OptionalExamples.User user)

Wraps a possibly null user email in an Optional.

Parameters:

user - the user to inspect, which may be null

Returns:

an Optional containing the email when both user and email exist

displayEmail

public String displayEmail(OptionalExamples.User user)

Uses Optional.orElse(Object) to provide a default value.

Parameters:

user - the user to inspect

Returns:

the user's email, or a default message when the email is missing

displayEmailGeneratedLazily

public String displayEmailGeneratedLazily(OptionalExamples.User user)

Uses Optional.orElseGet(java.util.function.Supplier) to create a fallback only when the Optional is empty.

Parameters:

user - the user to inspect

Returns:

the user's email, or a lazily generated fallback message

requireEmail

public String requireEmail(OptionalExamples.User user)

Uses Optional.orElseThrow(java.util.function.Supplier) when the missing value should be treated as an error.

Parameters:

user - the user to inspect

Returns:

the required email

normalizeEmail

public Optional<String> normalizeEmail(OptionalExamples.User user)

Transforms and validates a value while it is inside an Optional.

Parameters:

user - the user to inspect

Returns:

a normalized email when a valid email is present

findCompanyDomain

public Optional<String> findCompanyDomain(OptionalExamples.User user)

Uses Optional.flatMap(java.util.function.Function) when the transformation already returns an Optional.

Parameters:

user - the user to inspect

Returns:

the company email domain, excluding personal Gmail addresses