This is the tutorial on java.util.Optional<T>

You're supposed to be familiar with OOP, have basic knowledge of JDK, and be able to write Java code.

• Tutorial on Lamdbas
• Tutorial on Stream API

When writing a method that is not able to return a value in some cases, there are three options:

• return null
• throw an exception
• return Optinonal<T>

Returning null is obliously the most error prone approach. If you want to be safe, you should somehow force clients of your method to handle the possible lack of value. For that purpose you can use checked exceptoins. Although this approach is safe it has two disatvantages: thowing exceptoin is an expansive operatoin, and it brings addtional boilerplate. The better approach is to use Optional<T>, which is safe and concise.

Optional<T> is a like a collection that can hold at most one value. It provides usefull methods to replace imperative old-style null-checks. It also contains convenient methods for working with Stream API. In general, Optional API follows the similar functional-style approach as streams.

• prefer Optional-returning method in case the lack of value is possible
• return Optional from methods (e.g. getter), do not wrap instance fields
• prefer methods like Optional#ifPresent() over imperative if statements
• never return null from an Optional-returning method
• always use special supplier-based method Optional#orElseGet() in case it is expensive to compute default value
• do not wrap with optional arrays, collections, streams, and maps
• use special classes for primitive types (e.g. OptionalInt)
• avoid using Optional for performance-critical cases