map(Employee::getId) // get ID from employee if there is one map(EmployeeService::getEmployee) // getEmployee() might return null I'd opt toward: Optional.of(employeeService) // definitely have the service E.g., where you wrote: Optional employeeOptional = Optional.ofNullable(employeeService.getEmployee()) Įmployee employeeOptional= employeeOptional.get() That will look like this: String managerName = you're using Optional as a 'compatibility' layer between an older API that may still return null, it may be helpful to create the (non-empty) Optional at the latest stage that you're sure that you have something.

Say Bob belongs to a department, and we want to get the name of the department manager. To prevent an object from taking on a null value, programmers typically resort to doing additional checks like this: String a = null Īnd of course, that's all fine, until we want to do something more complex. When the above code is run, an NPE will be thrown on line 2 because a null object has no methods. To see how it happens, let's take a look at the piece of Java code below: String a = null In fact, About one third of app crashes can be attributed to NPE. When developing Android applications in Java, NullPointerException (NPE) was a big problem. At execution time, the reference to object can be void, leading to run-time exceptions (In the case of Java, a NullPointerException) and often abnormal termination of the program. A typical function call is of the form object.func() object denotes a reference to a certain object, and func denotes a function call. In object-oriented languages, access to objects is achieved through references. Null Safety (or void safety) is the guarantee that no object reference will have a null value. This document explains Kotlin's null safety feature.

But I couldn't resist the temptation to put in a null reference, simply because it was so easy to implement.” It was the invention of the null reference…My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler.

Kotlin optional to nullable