Head First Java. 3rd Edition Kathy Sierra, Bert Bates, Trisha Gee

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• Other books in OReillys Head First series
• Table of Contents (the real thing)
• How to Use This Book: Intro
  • Who is this book for?
    • Who should probably back away from this book?
  • We know what youre thinking
  • And we know what your brain is thinking
  • Metacognition: thinking about thinking
  • Heres what WE did:
  • Heres what YOU can do to bend your brain into submission
  • What you need for this book:
  • Last-minute things you need to know:
  • Technical Reviewers for the 3rd Edition
  • Other people to acknowledge for the 3rd Edition
  • Technical Editors for the 2nd Edition
  • Other people to credit, for the 2nd Edition
  • Just when you thought there wouldnt be any more acknowledgments*
• 1. Breaking the Surface: Dive In: A Quick Dip
  • The way Java works
  • What youll do in Java
  • A very brief history of Java
    • Speed and memory usage
  • Code structure in Java
    • What goes in a source file?
    • What goes in a class?
    • What goes in a method?
  • Anatomy of a class
  • Writing a class with a main()
  • What can you say in the main method?
  • Looping and looping and...
    • Simple boolean tests
    • Example of a while loop
  • Conditional branching
  • Coding a serious business application
  • Monday morning at Bobs Java-enabled house
  • Phrase-O-Matic
    • How it works
  • Exercise
    • Code Magnets
    • BE the Compiler
    • JavaCross
    • Mixed Messages
    • Pool Puzzle
  • Exercise Solutions
    • Sharpen your pencil
    • Code Magnets
    • BE the Compiler
    • Pool Puzzle
    • JavaCross
    • Mixed Messages
• 2. A Trip to Objectville: Classes and Objects
  • Chair Wars
    • (or How Objects Can Change Your Life)
    • At Lauras desk
    • At Brads laptop at the cafe
      • Laura thought shed nailed it. She could almost feel the rolled steel of the Aeron beneath her...
      • But wait! Theres been a spec change.
    • Back at Lauras desk
    • At Brads laptop at the beach
      • Laura delivered just moments ahead of Brad
    • Back at Lauras desk
    • At Brads laptop on his lawn chair at the Telluride Bluegrass Festival
    • So, Brad the OO guy got the chair and desk, right?
    • What about the Amoeba rotate()?
    • The suspense is killing me. Who got the chair and desk?
    • When you design a class, think about the objects that will be created from that class type. Think about:
      • Things an object knows about itself are called
      • Things an object can do are called
  • Whats the difference between a class and an object?
    • A class is not an object (but its used to construct them)
  • Making your first object
  • Making and testing Movie objects
  • Quick! Get out of main!
    • The two uses of main:
    • The Guessing Game
  • Running the Guessing Game
  • Exercise
    • BE the Compiler
    • Code Magnets
    • Pool Puzzle
    • Who Am I?
  • Exercise Solutions
    • Code Magnets
    • BE the Compiler
    • Puzzle Solutions
      • Pool Puzzle
    • Who Am I?
• 3. Know Your Variables: Primitives and References
  • Declaring a variable
  • Id like a double mocha, no, make it an int.
    • Primitive Types
  • You really dont want to spill that...
  • Back away from that keyword!
  • This table reserved
  • Controlling your Dog object
  • An object reference is just another variable value
  • Java Exposed
    • Life on the garbage-collectible heap
    • Life and death on the heap
  • An array is like a tray of cups
  • Arrays are objects too
  • Make an array of Dogs
  • Control your Dog (with a reference variable)
  • What happens if the Dog is in a Dog array?
  • A Dog example
  • Exercise
    • BE the Compiler
    • Code Magnets
    • Pool Puzzle
    • A Heap o Trouble
    • The case of the pilfered references
    • Five-Minute Mystery
  • Exercise Solutions
    • Sharpen your pencil
    • Code Magnets
    • BE the Compiler
    • Puzzle Solutions
      • Pool Puzzle
    • Five-Minute Mystery
    • A Heap o Trouble
• 4. How Objects Behave: Methods Use Instance Variables
  • Remember: a class describes what an object knows and what an object does
    • Can every object of that type have different method behavior?
  • The size affects the bark
  • You can send things to a method
  • You can get things back from a method
  • You can send more than one thing to a method
    • Calling a two-parameter method and sending it two arguments
    • You can pass variables into a method, as long as the variable type matches the parameter type
  • Java is pass-by-value. That means pass-by-copy.
  • Reminder: Java cares about type!
  • Cool things you can do with parameters and return types
  • Encapsulation
    • Do it or risk humiliation and ridicule.
    • Hide the data
  • Java Exposed
  • Encapsulating the GoodDog class
  • How do objects in an array behave?
  • Declaring and initializing instance variables
  • The difference between instance and local variables
  • Comparing variables (primitives or references)
  • Exercise
    • BE the Compiler
    • Who Am I?
    • Mixed Messages
    • Pool Puzzle
    • Five-Minute Mystery
  • Exercise Solutions
    • Sharpen your pencil
    • BE the Compiler
    • Who Am I?
    • Puzzle Solutions
      • Pool Puzzle
    • Five-Minute Mystery
    • Mixed Messages
• 5. Extra-Strength Methods: Writing A Program
  • Lets build a Battleship-style game: Sink a Startup
  • First, a high-level design
  • The Simple Startup Game a gentler introduction
  • Developing a Class
    • The three things well write for each class:
  • Writing the method implementations
  • Writing test code for the SimpleStartup class
    • Based on this prep code:
    • Heres what we should test:
  • Test code for the SimpleStartup class
  • The checkYourself() method
  • Just the new stuff
  • Final code for SimpleStartup and SimpleStartupTestDrive
  • Prep code for the SimpleStartupGame class Everything happens in main()
  • The games main() method
  • random() and getUserInput()
  • One last class: GameHelper
  • Lets play
  • Whats this? A bug ?
    • Gasp!
  • More about for loops
    • Regular (non-enhanced) for loops
  • Trips through a loop
    • Difference between for and while
  • The enhanced for loop
  • Casting primitives
  • Exercise
    • BE the JVM
    • Code Magnets
    • JavaCross
    • Mixed Messages
  • Exercise Solutions
    • Be the JVM
    • Code Magnets
    • Puzzle Solutions
    • JavaCross
    • Mixed Messages
• 6. Using the Java Library: Get to Know the Java API
  • In our last chapter, we left you with the cliff-hanger: a bug
    • How its supposed to look
    • How the bug looks
  • So what happened?
  • How do we fix it?
  • Option one is too clunky
  • Option two is a little better, but still pretty clunky
  • Wake up and smell the library
  • Some things you can do with ArrayList
  • Java Exposed
  • Solution
    • Sharpen your pencil
  • Comparing ArrayList to a regular array
  • Lets fix the Startup code
  • New and improved Startup class
  • Lets build the REAL game: Sink a Startup
  • What needs to change?
  • Who does what in the StartupBust game (and when)
  • Prep code for the real StartupBust class
  • The final version of the Startup class
  • Super powerful Boolean expressions
  • Ready-Bake Code
  • Using the Library (the Java API)
  • You have to know the full name* of the class you want to use in your code.
  • How to discover the API
  • Browse a book
  • Use the HTML API docs
  • Using the class documentation
  • Exercise
    • Code Magnets
    • JavaCross
  • Exercise Solutions
    • Code Magnets
    • JavaCross
• 7. Better Living in Objectville: Inheritance and Polymorphism
  • Chair Wars Revisited...
  • What about the Amoeba rotate()?
  • Understanding Inheritance
  • An inheritance example:
  • Lets design the inheritance tree for an Animal simulation program
  • Using inheritance to avoid duplicating code in subclasses
  • Do all animals eat the same way?
    • Which methods should we override?
  • Looking for more inheritance opportunities
  • Which method is called?
  • Designing an Inheritance Tree
  • Using IS-A and HAS-A
  • But wait! Theres more!
  • How do you know if youve got your inheritance right?
  • When designing with inheritance, are you using or abusing?
  • So what does all this inheritance really buy you?
  • Inheritance lets you guarantee that all classes grouped under a certain supertype have all the methods that the supertype has*
  • Keeping the contract: rules for overriding
  • Overloading a method
  • Exercise
    • Mixed Messages
    • BE the Compiler
  • Exercise Solutions
    • BE the Compiler
    • Mixed Messages
    • Pool Puzzle
• 8. Serious Polymorphism: Interfaces and Abstract Classes
  • Did we forget about something when we designed this?
  • The compiler wont let you instantiate an abstract class
  • Abstract vs. Concrete
  • Abstract methods
  • You MUST implement all abstract methods
  • Polymorphism in action
  • Uh-oh, now we need to keep Cats, too
  • What about non-Animals? Why not make a class generic enough to take anything?
  • So whats in this ultra-super-megaclass Object?
  • Using polymorphic references of type Object has a price...
  • When a Dog wont act like a Dog
  • Objects dont bark
  • Get in touch with your inner Object
  • Polymorphism means many forms.
    • Casting an object reference back to its real type.
  • What if you need to change the contract?
  • Lets explore some design options for reusing some of our existing classes in a PetShop program
  • Interface to the rescue!
  • Making and implementing the Pet interface
  • Invoking the superclass version of a method
  • Exercise
    • Pool Puzzle
  • Exercise Solutions
    • Whats the Picture ?
    • Whats the Declaration?
    • Pool Puzzle
• 9. Life and Death of an Object: Constructors and Garbage Collection
  • The Stack and the Heap: where things live
  • Methods are stacked
    • A stack scenario
  • What about local variables that are objects?
  • If local variables live on the stack, where do instance variables live?
  • The miracle of object creation
  • Construct a Duck
  • Initializing the state of a new Duck
  • Using the constructor to initialize important Duck state*
  • Make it easy to make a Duck
    • Be sure you have a no-arg constructor
  • Doesnt the compiler always make a no-arg constructor for you? No!
  • Nanoreview: four things to remember about constructors
  • Wait a minute...we never DID talk about superclasses and inheritance and how that all fits in with constructors
  • The role of superclass constructors in an objects life
  • Making a Hippo means making the Animal and Object parts too...
  • How do you invoke a superclass constructor?
  • Can the child exist before the parents?
  • Superclass constructors with arguments
  • Invoking one overloaded constructor from another
  • Now we know how an object is born, but how long does an object live?
  • What about reference variables?
  • Exercise
    • BE the Garbage Collector
    • Popular Objects
    • Five-Minute Mystery
  • Exercise Solutions
    • Be the Garbage Collector
    • Popular Objects
    • Five-Minute Mystery
• 10. Numbers Matter: Numbers and Statics
  • MATH methods: as close as youll ever get to a global method
  • The difference between regular (non-static) and static methods
  • What it means to have a class with static methods
  • Static methods cant use non-static (instance) variables!
  • Static methods cant use non-static methods, either!
  • Static variable: value is the same for ALL instances of the class
    • Initializing a static variable
  • static final variables are constants
  • final isnt just for static variables...
  • Math methods
  • Wrapping a primitive
  • Java will Autobox primitives for you
  • Autoboxing works almost everywhere
  • But wait! Theres more! Wrappers have static utility methods too!
  • And now in reverse...turning a primitive number into a String
  • Number formatting
  • Formatting deconstructed...
  • The percent (%) says, insert argument here (and format it using these instructions)
  • The format String uses its own little language syntax
  • The format specifier
  • The only required specifier is for TYPE
  • What happens if I have more than one argument?
  • Just one more thing...static imports
  • Fireside Chats
  • Exercise
    • BE the compiler
    • True or False
  • Exercise Solution
    • Sharpen your pencil
    • BE the compiler
    • True or False
• 11. Data Structures: Collections and Generics
  • Tracking song popularity on your jukebox
  • Your first job, sort the songs in alphabetical order
  • Great question! You spotted the diamond operator
  • Exploring the java.util API, List and Collections
  • In the Real-World there are lots of ways to sort
  • Natural Ordering, what Java means by alphabetical
  • But now you need Song objects, not just simple Strings
  • Changing the Jukebox code to use Songs instead of Strings
  • It wont compile!
  • The sort() method declaration
  • Generics means more type-safety
  • Learning generics
  • Using generic CLASSES
  • Using type parameters with ArrayList
  • Using generic METHODS
  • Heres where it gets weird...
  • Revisiting the sort() method
  • In generics, extends means extends or implements
  • Finally we know whats wrong...
    • The Song class needs to implement Comparable
  • The new, improved, comparable Song class
  • We can sort the list, but...
  • Using a custom Comparator
  • Updating the Jukebox to use a Comparator
  • Fill-in-the-blanks
  • But wait! Were sorting in two different ways!
  • Sorting using only Comparators
  • Just the code that matters
  • What do we REALLY need in order to sort?
  • Enter lambdas! Leveraging what the compiler can infer
  • Where did all that code go?
  • Some interfaces have only ONE method to implement
  • Updating the Jukebox code with lambdas
  • Reverse Engineer
  • Uh-oh. The sorting all works, but now we have duplicates...
  • We need a Set instead of a List
  • The Collection API (part of it)
  • Using a HashSet instead of ArrayList
  • What makes two objects equal?
  • How a HashSet checks for duplicates: hashCode() and equals()
  • The Song class with overridden hashCode() and equals()
  • If we want the set to stay sorted, weve got TreeSet
  • What you MUST know about TreeSet...
  • TreeSet elements MUST be comparable
  • Weve seen Lists and Sets, now well use a Map
  • Creating and filling collections
  • Convenience Factory Methods for Collections
  • Finally, back to generics
    • Using polymorphic arguments and generics
  • But will it work with List<Dog>?
  • What could happen if it were allowed...?
  • We can do this with wildcards
  • Using the methods generic type parameter
  • Exercise
    • BE the Compiler, advanced
  • Exercise Solution
    • Fill-in-the-blanks
    • Reverse Engineer lambdas exercise
    • Sorting with lambdas
    • TreeSet exercise
    • BE the Compiler solution
• 12. Lambdas and Streams: What, Not How: Lambdas and Streams
  • Tell the computer WHAT you want
  • Fireside Chats
  • When for loops go wrong
    • Mixed Messages
  • Small errors in common code can be hard to spot
  • Building blocks of common operations
  • Introducing the Streams API
  • Getting started with Streams
  • Streams are like recipes: nothings going to happen until someone actually cooks them
  • Getting a result from a Stream
  • Stream operations are building blocks
  • Building blocks can be stacked and combined
  • Customizing the building blocks
  • Create complex pipelines block by block
  • Yes, because Streams are lazy
  • Terminal operations do all the work
  • Collecting to a List
  • Guidelines for working with streams
    • Correct! Stream operations dont change the original collection.
  • Exercise
    • Code Magnets
  • Hello Lambda, my (not so) old friend
    • Passing behavior around
      • Lambda expressions are objects, and you run them by calling their Single Abstract Method
  • The shape of lambda expressions
  • Anatomy of a lambda expression
  • Variety is the spice of life
    • A lambda might have more than one line
    • Single-line lambdas dont need ceremony
    • A lambda might not return anything
    • A lambda might have zero, one, or many parameters
  • How can I tell if a method takes a lambda?
  • Exercise
    • BE the Compiler, advanced
  • Spotting Functional Interfaces
  • Functional interfaces in the wild
  • Lous back!
  • Exercise
  • Ready-Bake Code
  • Lous Challenge #1: Find all the rock songs
  • Filter a stream to keep certain elements
  • Lets Rock!
  • Getting clever with filters
  • Lous Challenge #2: List all the genres
  • Mapping from one type to another
  • Removing duplicates
  • Only one of every genre
  • Just keep building!
  • Sometimes you dont even need a lambda expression
  • Collecting results in different ways
  • But wait, theres more!
    • Checking if something exists
    • Find a specific thing
    • Count the items
    • Well, some operations may return something, or may not return anything at all
  • Optional is a wrapper
    • Yes, but now we have a way to ask if we have a result
  • Dont forget to talk to the Optional wrapper
    • The Unexpected Coffee
    • Five-Minute Mystery
    • Pool Puzzle
    • Mixed Messages
    • Who Does What?
  • Exercise Solutions
    • Code Magnets
    • BE the Compiler
    • Sharpen your pencil
    • Five-Minute Mystery
    • Pool Puzzle
• 13. Risky Behavior: Exception Handling
  • Lets make a Music Machine
    • The finished BeatBox looks something like this:
  • Well start with the basics
    • The JavaSound API
  • First we need a Sequencer
    • Somethings wrong!
  • What happens when a method you want to call (probably in a class you didnt write) is risky?
  • Methods in Java use exceptions to tell the calling code, Something Bad Happened. I failed.
  • The compiler needs to know that YOU know youre calling a risky method
  • An exception is an object... of type Exception
  • If its your code that catches the exception, then whose code throws it?
  • Flow control in try/catch blocks
  • Finally: for the things you want to do no matter what
  • Flow Control
  • Did we mention that a method can throw more than one exception?
    • Catching multiple exceptions
  • Exceptions are polymorphic
  • Multiple catch blocks must be ordered from smallest to biggest
  • You cant put bigger baskets above smaller baskets
  • When you dont want to handle an exception...
  • Ducking (by declaring) only delays the inevitable
  • Getting back to our music code...
    • Exception Rules
  • Code Kitchen
  • Making actual sound
  • Version 1: Your very first sound player app
  • Making a MidiEvent (song data)
  • MIDI message: the heart of a MidiEvent
    • Anatomy of a message
  • Change a message
  • Version 2: Using command-line args to experiment with sounds
    • Where were headed with the rest of the CodeKitchens
  • Exercise
    • True or False
    • Code Magnets
    • JavaCross
    • Sharpen your pencil
  • Exercise Solution
    • True or False
    • Code Magnets
    • JavaCross
• 14. A Very Graphic Story: Getting Gui
  • It all starts with a window
    • Put widgets in the window
  • Your first GUI: a button on a frame
  • But nothing happens when I click it...
  • Getting a user event
  • Listeners, Sources, and Events
  • Getting back to graphics...
  • Make your own drawing widget
  • Fun things to do in paintComponent()
  • Behind every good Graphics reference is a Graphics2D object
  • Because lifes too short to paint the circle a solid color when theres a gradient blend waiting for you
  • We can get an event. We can paint graphics. But can we paint graphics when we get an event?
  • GUI layouts: putting more than one widget on a frame
  • Lets try it with TWO buttons
  • So now we need FOUR widgets
  • And we need to get TWO events
    • How do you get action events for two different buttons when each button needs to do something different?
  • Inner class to the rescue!
  • An inner class instance must be tied to an outer class instance*
  • How to make an instance of an inner class
    • Java Exposed
  • Lambdas to the rescue! (again)
  • ActionListener is a Functional Interface
  • Lambdas, clearer and more concise
  • Using an inner class for animation
  • Code Kitchen
  • Listening for a non-GUI event
  • An easier way to make messages/events
  • Version One: using the new static makeEvent() method
  • Version Two: registering and getting ControllerEvents
  • Version Three: drawing graphics in time with the music
  • Exercise
    • Who Am I?
    • BE the Compiler
    • Pool Puzzle
  • Exercise Solutions
    • Who am I?
    • BE the Compiler
    • Pool Puzzle
• 15. Work on Your Swing: Using Swing
  • Swing components
    • Components can be nested
  • Layout Managers
  • How does the layout manager decide?
    • Different layout managers have different policies
  • The Big Three layout managers: border, flow, and box
  • Playing with Swing components
  • Code Kitchen
  • Making the BeatBox
  • Exercise
    • Which code goes with which layout?
    • Code Fragments
    • GUI-Cross
  • Exercise Solutions
    • Which code goes with which layout?
    • GUI-Cross
• 16. Saving Objects (and Text): Serialization and File I/O
  • Capture the beat
  • Saving state
  • Writing a serialized object to a file
  • Data moves in streams from one place to another
  • What really happens to an object when its serialized?
  • But what exactly IS an objects state? What needs to be saved?
  • If you want your class to be serializable, implement Serializable
  • Deserialization: restoring an object
  • What happens during deserialization?
  • Saving and restoring the game characters
    • The GameCharacter class
  • Version ID: A big serialization gotcha
  • Using the serialVersionUID
  • Object Serialization
  • Writing a String to a Text File
  • Text file example: e-Flashcards
  • Quiz Card Builder (code outline)
  • The java.io.File class
  • Reading from a text file
  • Quiz Card Player (code outline)
  • Parsing with String split()
  • NIO.2 and the java.nio.file package
  • Path, Paths, and Files (messing with directories)
  • Finally, a closer look at finally
  • Remember, finally ALWAYS runs!!
  • Finally, a closer look at finally, cont.
  • There IS a better way!
  • The try-with-resources (TWR), statement
  • Autocloseable, the very small catch
  • Autocloseable, its everywhere you do I/O
  • Code Kitchen
  • Saving a BeatBox pattern
  • Restoring a BeatBox pattern
  • Can they be saved?
  • Exercise
    • True or False
    • Code Magnets
  • Exercise Solutions
    • True or False
    • Code Magnets
• 17. Make a Connection: Networking and Threads
  • Real-time BeatBox chat
  • Connecting, sending, and receiving
  • 1. Connect
  • 2. Receive
    • Reading from the network with BufferedReader
  • 3. Send
    • Writing to the network with PrintWriter
  • Theres more than one way to make a connection
    • Using a Socket
  • The DailyAdviceClient
  • DailyAdviceClient code
  • Writing a simple server application
  • DailyAdviceServer code
  • Writing a Chat Client
  • The really, really simple Chat Server
  • Java has multiple threads but only one Thread class
  • What does it mean to have more than one call stack?
  • To create a new call stack you need a job to run
  • To make a job for your thread, implement the Runnable interface
  • How NOT to run the Runnable
  • How we used to launch a new thread
  • A better alternative: dont manage the Threads at all
  • Running one job
    • The three states of a new thread
  • The thread scheduler
    • How did we end up with different results?
  • Putting a thread to sleep
  • Using sleep to make our program more predictable
  • There are downsides to forcing the thread to sleep
  • Counting down until ready
  • Making and starting two threads (or more!)
  • Pooling Threads
  • Running multiple threads
  • What will happen?
  • Closing time at the thread pool
  • Um, yes. There IS a dark side. Multithreading can lead to concurrency issues.
  • Exercise
    • Who Am I?
  • New and improved SimpleChatClient
  • Exercise
    • Code Magnets
  • Exercise Solutions
    • Who Am I?
    • Code Magnets
    • Code Kitchen
• 18. Dealing with Concurrency Issues: Race Conditions and Immutable Data
  • What could possibly go wrong?
  • The Ryan and Monica problem, in code
  • The Ryan and Monica example
  • We need to check the balance and spend the money as one atomic thing
  • Using an objects lock
  • Using synchronized methods
  • Its important to lock the correct object
  • The dreaded Lost Update problem
  • Lets run this code...
  • Make the increment() method atomic. Synchronize it!
  • Deadlock, a deadly side of synchronization
  • You dont always have to use synchronized
    • Atomic variables
  • Compare-and-swap with atomic variables
  • Ryan and Monica, going atomic
  • Writing a class for immutable data
  • Using immutable objects
  • Changing immutable data
  • More problems with shared data
  • Reading from a changing data structure causes an Exception
  • Use a thread-safe data structure
  • CopyOnWriteArrayList
  • Exercise
    • BE the JVM
      • Near-miss at the airlock
    • Five-Minute Mystery
  • Exercise Solution
    • BE the JVM
    • Five-Minute Mystery
• A. Final Code Kitchen
  • Final BeatBox client program
  • Final BeatBox server program
• B. The top ten-ish topics that didnt make it into the rest of the book...
  • #11 JShell (Java REPL)
    • Why do you care?
      • Starting the REPL
      • Run Java code without a class
      • More than just lines of code
      • Code suggestions
      • Commands
  • #10 Packages
    • Packages prevent class name conflicts
    • Preventing package name conflicts
      • To put your class in a package:
      • A note on directories
    • Compiling and running with packages
      • Compiling with the -d (directory) flag
      • Running your code
  • #9 Immutability in Strings and Wrappers
    • Why do you care that Strings are immutable?
      • How does this save memory?
      • Immutability makes reuse possible
      • What happens to unused Strings?
    • Why do you care that Wrappers are immutable?
  • #8 Access levels and access modifiers (who sees what)
  • #7 Varargs
    • Why do you care?
      • How can I tell if a method takes varargs?
      • Creating a method that takes varargs
      • Rules
  • #6 Annotations
    • Why do you care?
      • Where will you see annotations?
      • Annotations can have elements
      • What do they do?
  • #5 Lambdas and Maps
    • Why do you care?
      • Create a new value if there isnt one for the key
      • Update the value only if it already exists
      • Other methods
  • #4 Parallel Streams
    • Going parallel
    • OK now what?
    • Multithreading is taken care of
    • Do not use parallel everywhere!
  • #3 Enumerations (also called enumerated types or enums)
    • Whos in the band?
    • The old way to fake an enum:
      • An official enum
      • Your enum extends java.lang.Enum
      • Using if and switch with enums
  • #2 Local Variable Type Inference (var)
    • Type inference, NOT dynamic types
    • Someone has to read your code
    • Tip: Better with useful variable names
    • Tip: Variable will be the concrete type
    • Tip: Dont use var with the diamond operator
  • #1 Records
    • Why do you care?
      • A Java data class, before Java 16
      • What if there was a special syntax for data classes?
      • Using a record
      • Goodbye get
      • You can override constructors
      • You can override or add methods
      • Records are immutable
• Index

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