Understanding Optional Class in Java Collections

The Optional class in Java is a powerful tool used to handle scenarios where a value may or may not be present. It provides methods like isPresent(), isEmpty(), and get() to work with potentially absent values. Optional.of() and Optional.empty() are key methods to create instances of Optional objects with or without a value. This class is particularly useful for enhancing code clarity and avoiding NullPointerExceptions in Java applications.

• Java Collections
• Optional Class
• Programming
• Error Handling
• Java Development

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1. LEC 15: Collections CSE 122 Winter 2023 BEFORE WE START Talk to your neighbors: coffee or tea? LEC 15 CSE 122 CSE 122 Collections Music: Miya s 23wi CSE 122 Playlist Instructor Miya Natsuhara TAs Ayush Connor Poojitha Andrew A Andrew C Jasmine Darel Gabe Karen Colton Atharva Julia Megana Joey Eesha Lilian Thomas Leon Melissa Audrey Ernie Di Logan Shivani Michelle Steven Kevin Ken Vivek Autumn Ambika Elizabeth Joe Jin Ben Evelyn Kent Questions during Class? Raise hand or send here sli.do #cse122

2. LEC 15: Collections CSE 122 Winter 2023 Lecture Outline Announcements Optional Recap of Collections Dumb Data Structures Collections

3. LEC 15: Collections CSE 122 Winter 2023 Announcements P3 will be released later today! - OOP, Interfaces Quiz 2 details posted - Take home - No enforced time limit - Collaboration permitted with caution Final Exam info posted

4. LEC 15: Collections CSE 122 Winter 2023 Lecture Outline Announcements Optional Recap of Collections Dumb Data Structures Collections

5. LEC 15: Collections CSE 122 Winter 2023 (PCM) Optional Optional is a Java class that is used to handle situations where a value is sometimes there. You give Optional a type to hold (or potentially not hold) when you are referring to its type. e.g., Optional<String>, Optional<Integer>, Optional<Point>

6. LEC 15: Collections CSE 122 Winter 2023 (PCM) Optional Methods Method Description Creates an empty Optional object Optional.empty() Creates an Optionalobject holding the object it s given Optional.of( ) Returns true if there isno value stored, and false otherwise isEmpty() Returns true if there is a value stored, and false otherwise isPresent() Returns the stored object from the Optional (if one is stored; otherwise throws a NoSuchElementException) get() The Optional class has more than just these methods, but these are what you ll need to focus on for this class!

7. LEC 15: Collections CSE 122 Winter 2023 (PCM) Optional Methods isEmpty(), isPresent(), and get() are called like normal instance methods (on an actual instance of Optional). Optional.of( ) and Optional.empty() are called differently (Like the Math class methods)

8. LEC 15: Collections CSE 122 Winter 2023 (PCM) Why Optional? Using Optional can help programmers avoid NullPointerExceptions by making it explicit when a variable may or may not contain a value. Remember null refers to the absence of an object! There are other Optional methods (that you should explore in your own time if you re interested) that can be really useful to cleanly work with data that may or may not be present.

9. LEC 15: Collections CSE 122 Winter 2023 Student / Course Example one more time Let s add two more methods to Course.java: public void setCourseEvalLink(String url) public Optional<String> getCourseEvalLink() The link to the evaluations for a course doesn t usually exist until the last few weeks of the quarter. What if a client calls getCourseEvalLink before one is set up? Optional to the rescue!

10. LEC 15: Collections CSE 122 Winter 2023 Lecture Outline Announcements Optional Recap of Collections Dumb Data Structures Collections

11. LEC 15: Collections CSE 122 Winter 2023 Goal for Today Review some of the data structures we ve talked about this quarter Understand how Java organizes them with interfaces

12. LEC 15: Collections CSE 122 Winter 2023 Collections: What classes have we seen so far?

13. LEC 15: Collections CSE 122 Winter 2023 Collections: What interfaces have we seen so far?

14. LEC 15: Collections CSE 122 Winter 2023 Lecture Outline Announcements Optional Recap of Collections Dumb Data Structures Collections

15. LEC 15: Collections CSE 122 Winter 2023 Dumb Data Structures We re going to create our own versions of these classes so we can dig into how they all relate to each other! BUT they re going to be real dumb. If you want to get a sense of how they re actually implemented, go take CSE 123!

16. LEC 15: Collections CSE 122 Winter 2023 DumbArrayIntList DumbArrayIntList() set(int index, int value) add(int value) remove(int index) add(int index, int value) size() contains(int value) indexOf(int value) isEmpty() toString() get(int index)

17. LEC 15: Collections CSE 122 Winter 2023 Lecture Outline Announcements Optional Recap of Collections Dumb Data Structures Collections

18. LEC 15: Collections CSE 122 Winter 2023 DumbIntCollection Relationships