A word about the java.util.Optional

Less nonsense:the Java.util.Optional class can significantly reduce null judgments and NullPointerException exceptions.

1. Optional.of

Optional.of (null); //

2. optional.ofnullable

Optional.ofnullable (null); // no exception reported

3. Optional.get

Optional.ofnullable (null). get (); // report NULL pointer exception

4. Optional.orelse

String test = optional.ofnullable (null//  test = "Hello,world" )

5. Optional.orelseget

Optional.ofnullable ("123"). Orelseget ((), "Never Carry out my"); // lazy calculation.

5. Optional.ispresent

This is no use, you have to use and XX! = NULL What is the difference?

6. Optional.map

Give you a list of students, how do you get back to the student's name list?

Optional.ofnullable (Stus). Map (Student::getname). OrElse (Collection.emptylist ());

7. Optional.flatmap

Give you a list of students, you are responsible for each student's preferences collected, and then organized into another list, how to do?

Optional.ofnullable (Stus). FlatMap (Stu-optional.ofnullable (Stu.getfavoutites ())). OrElse ( Collection.emptylist ());

A word about the java.util.Optional