How about computing the average weight of a melon?
For this, we have Collectors.averagingInt(), averagingLong(), and averagingDouble():
double avgWeights = melons.stream()
.collect(Collectors.averagingInt(Melon::getWeight));
- Title Page
- Copyright and Credits
- About Packt
- Contributors
- Preface
- Strings, Numbers, and Math
- Problems
- Solutions
- 1. Counting duplicate characters
- 2. Finding the first non-repeated character
- 3. Reversing letters and words
- 4. Checking whether a string contains only digits
- 5. Counting vowels and consonants
- 6. Counting the occurrences of a certain character
- 7. Converting a string into an int, long, float, or double
- 8. Removing white spaces from a string
- 9. Joining multiple strings with a delimiter
- 10. Generating all permutations
- 11. Checking whether a string is a palindrome
- 12. Removing duplicate characters
- 13. Removing a given character
- 14. Finding the character with the most appearances
- 15. Sorting an array of strings by length
- 16. Checking that a string contains a substring
- 17. Counting substring occurrences in a string
- 18. Checking whether two strings are anagrams
- 19. Declaring multiline strings (text blocks)
- 20. Concatenating the same string n times
- 21. Removing leading and trailing spaces
- 22. Finding the longest common prefix
- 23. Applying indentation
- 24. Transforming strings
- 25. Computing the minimum and maximum of two numbers
- 26. Summing two large int/long values and operation overflow
- 27. String as an unsigned number in the radix
- 28. Converting into a number by an unsigned conversion
- 29. Comparing two unsigned numbers
- 30. Division and modulo of unsigned values
- 31. double/float is a finite floating-point value
- 32. Applying logical AND/OR/XOR to two boolean expressions
- 33. Converting BigInteger into a primitive type
- 34. Converting long into int
- 35. Computing the floor of a division and modulus
- 36. Next floating-point value
- 37. Multiplying two large int/long values and operation overflow
- 38. Fused Multiply Add
- 39. Compact number formatting
- Summary
- Objects, Immutability, and Switch Expressions
- Problems
- Solutions
- 40. Checking null references in functional style and imperative code
- 41. Checking null references and throwing customized NullPointerException
- 42. Checking null references and throwing the specified exception
- 43. Checking null references and returning non-null default references
- 44. Checking the index in the range from 0 to length
- 45. Checking the subrange in the range from 0 to length
- 46. equals() and hashCode()
- 47. Immutable objects in a nutshell
- 48. Immutable string
- 49. Writing an immutable class
- 50. Passing/returning mutable objects to/from an immutable class
- 51. Writing an immutable class via the Builder pattern
- 52. Avoiding bad data in immutable objects
- 53. Cloning objects
- 54. Overriding toString()
- 55. Switch expressions
- 56. Multiple case labels
- 57. Statement blocks
- Summary
- Working with Date and Time
- Problems
- Solutions
- 58. Converting a string to date and time
- 59. Formatting date and time
- 60. Getting the current date/time without time/date
- 61. LocalDateTime from LocalDate and LocalTime
- 62. Machine time via an Instant class
- 63. Defining a period of time using date-based values and a duration of time using time-based values
- 64. Getting date and time units
- 65. Adding and subtracting to/from date-time
- 66. Getting all time zones with UTC and GMT
- 67. Getting local date-time in all available time zones
- 68. Displaying date-time information about a flight
- 69. Converting a Unix timestamp to date-time
- 70. Finding the first/last day of the month
- 71. Defining/extracting zone offsets
- 72. Converting between Date and Temporal
- 73. Iterating a range of dates
- 74. Calculating age
- 75. Start and end of a day
- 76. Difference between two dates
- 77. Implementing a chess clock
- Summary
- Type Inference
- Problems
- Solutions
- 78. Simple var example
- 79. Using var with primitive types
- 80. Using var and implicit type casting to sustain the code's maintainability
- 81. Explicit downcast or better avoid var
- 82. Avoid using var if the called names don't contain enough type information for humans
- 83. Combining LVTI and programming to the interface technique
- 84. Combining LVTI and the diamond operator
- 85. Assigning an array to var
- 86. Using LVTI in compound declarations
- 87. LVTI and variable scope
- 88. LVTI and the ternary operator
- 89. LVTI and for loops
- 90. LVTI and streams
- 91. Using LVTI to break up nested/large chains of expressions
- 92. LVTI and the method return and argument types
- 93. LVTI and anonymous classes
- 94. LVTI can be final and effectively final
- 95. LVTI and lambdas
- 96. LVTI and null initializers, instance variables, and catch blocks variables
- 97. LVTI and generic types, T
- 98. LVTI, wildcards, covariants, and contravariants
- Summary
- Arrays, Collections, and Data Structures
- Problems
- Solutions
- 99. Sorting an array
- 100. Finding an element in an array
- 101. Checking whether two arrays are equal or mismatches
- 102. Comparing two arrays lexicographically
- 103. Creating a Stream from an array
- 104. Minimum, maximum, and average of an array
- 105. Reversing an array
- 106. Filling and setting an array
- 107. Next Greater Element
- 108. Changing array size
- 109. Creating unmodifiable/immutable collections
- 110. Mapping a default value
- 111. Computing whether absent/present in a map
- 112. Removal from a Map
- 113. Replacing entries from a Map
- 114. Comparing two maps
- 115. Sorting a Map
- 116. Copying HashMap
- 117. Merging two maps
- 118. Removing all elements of a collection that match a predicate
- 119. Converting a collection into an array
- 120. Filtering a Collection by a List
- 121. Replacing elements of a List
- 122. Thread-safe collections, stacks, and queues
- 123. Breadth-first search
- 124. Trie
- 125. Tuple
- 126. Union Find
- 127. Fenwick Tree or Binary Indexed Tree
- 128. Bloom filter
- Summary
- Java I/O Paths, Files, Buffers, Scanning, and Formatting
- Problems
- Solutions
- 129. Creating file paths
- 130. Converting file paths
- 131. Joining file paths
- 132. Constructing a path between two locations
- 133. Comparing file paths
- 134. Walking paths
- 135. Watching paths
- 136. Streaming a file's content
- 137. Searching for files/folders in a file tree
- 138. Reading/writing text files efficiently
- 139. Reading/writing binary files efficiently
- 140. Searching in big files
- 141. Reading a JSON/CSV file as an object
- 142. Working with temporary files/folders
- 143. Filtering files
- 144. Discovering mismatches between two files
- 145. Circular byte buffer
- 146. Tokenizing files
- 147. Writing formatted output directly to a file
- 148. Working with Scanner
- Summary
- Java Reflection Classes, Interfaces, Constructors, Methods, and Fields
- Problems
- Solutions
- 149. Inspecting packages
- 150. Inspecting classes
- Get the name of the Pair class via an instance
- Getting the Pair class modifiers
- Getting the Pair class implemented interfaces
- Getting the Pair class constructors
- Getting the Pair class fields
- Getting the Pair class methods
- Getting the Pair class module
- Getting the Pair class superclass
- Getting the name of a certain type
- Getting a string that describes the class
- Getting the type descriptor string for a class
- Getting the component type of an array
- Getting a class for an array type whose component type is described by Pair
- 151. Instantiating via a reflected constructor
- 152. Getting the annotation of a receiver type
- 153. Getting synthetic and bridge constructs
- 154. Checking the variable number of arguments
- 155. Checking default methods
- 156. Nest-based access control via reflection
- 157. Reflection for getters and setters
- 158. Reflecting annotations
- Inspecting package annotations
- Inspecting class annotations
- Inspecting methods annotations
- Inspecting annotations of the thrown exceptions
- Inspecting annotations of the return type
- Inspecting annotations of the method's parameters
- Inspecting annotations of fields
- Inspecting annotations of the superclass
- Inspecting annotations of interfaces
- Get annotations by type
- Get a declared annotation
- 159. Invoking an instance method
- 160. Getting static methods
- 161. Getting generic types of method, fields, and exceptions
- 162. Getting public and private fields
- 163. Working with arrays
- 164. Inspecting modules
- 165. Dynamic proxies
- Summary
- Functional Style Programming - Fundamentals and Design Patterns
- Problems
- Solutions
- 166. Writing functional interfaces
- 167. Lambdas in a nutshell
- 168. Implementing the Execute Around pattern
- 169. Implementing the Factory pattern
- 170. Implementing the Strategy pattern
- 171. Implementing the Template Method pattern
- 172. Implementing the Observer pattern
- 173. Implementing the Loan pattern
- 174. Implementing the Decorator pattern
- 175. Implementing the Cascaded Builder pattern
- 176. Implementing the Command pattern
- Summary
- Functional Style Programming - a Deep Dive
- Problems
- Solutions
- 177. Testing high-order functions
- 178. Testing methods that use lambdas
- 179. Debugging lambdas
- 180. Filtering the non-zero elements of a stream
- 181. Infinite streams, takeWhile(), and dropWhile()
- 182. Mapping the elements of a stream
- 183. Finding elements in a stream
- 184. Matching elements in a stream
- 185. Sum, max, and min in a stream
- 186. Collecting the result of a stream
- 187. Joining the results of a stream
- 188. Summarization collectors
- 189. Grouping
- 190. Partitioning
- 191. Filtering, flattening, and mapping collectors
- 192. Teeing
- 193. Writing a custom collector
- The supplier – Supplier<A> supplier();
- Accumulating elements – BiConsumer<A, T> accumulator();
- Applying the final transformation – Function<A, R> finisher();
- Parallelizing the collector – BinaryOperator<A> combiner();
- Returning the final result – Function<A, R> finisher();
- Characteristics – Set<Characteristics> characteristics();
- Testing time
- Custom collecting via collect()
- 194. Method reference
- 195. Parallel processing of streams
- 196. Null-safe streams
- 197. Composing functions, predicates, and comparators
- 198. Default methods
- Summary
- Concurrency - Thread Pools, Callables, and Synchronizers
- Problems
- Solutions
- 199. Thread life cycle states
- 200. Object- versus class-level locking
- 201. Thread pools in Java
- 202. Thread pool with a single thread
- 203. Thread pool with a fixed number of threads
- 204. Cached and scheduled thread pools
- 205. Work-stealing thread pool
- 206. Callable and Future
- 207. Invoking multiple Callable tasks
- 208. Latches
- 209. Barrier
- 210. Exchanger
- 211. Semaphores
- 212. Phasers
- Summary
- Concurrency - Deep Dive
- Problems
- Solutions
- 213. Interruptible methods
- 214. Fork/join framework
- 215. Fork/join framework and compareAndSetForkJoinTaskTag()
- 216. CompletableFuture
- Running asynchronous task and return void
- Running an asynchronous task and returning a result
- Running an asynchronous task and returning a result via an explicit thread pool
- Attaching a callback that processes the result of an asynchronous task and returns a result
- Attaching a callback that processes the result of an asynchronous task and returns void
- Attaching a callback that runs after an asynchronous task and returns void
- Handling exceptions of an asynchronous task via exceptionally()
- JDK 12 exceptionallyCompose()
- Handling exceptions of an asynchronous task via handle()
- Explicitly complete a CompletableFuture
- 217. Combining multiple CompletableFuture instances
- 218. Optimizing busy waiting
- 219. Task Cancellation
- 220. ThreadLocal
- 221. Atomic variables
- 222. ReentrantLock
- 223. ReentrantReadWriteLock
- 224. StampedLock
- 225. Deadlock (dining philosophers)
- Summary
- Optional
- Problems
- Solutions
- 226. Initializing Optional
- 227. Optional.get() and missing value
- 228. Returning an already-constructed default value
- 229. Returning a non-existent default value
- 230. Throwing NoSuchElementException
- 231. Optional and null references
- 232. Consuming a present Optional class
- 233. Returning a present Optional class or another one
- 234. Chaining lambdas via orElseFoo()
- 235. Do not use Optional just for getting a value
- 236. Do not use Optional for fields
- 237. Do not use Optional in constructor args
- 238. Do not use Optional in setter args
- 239. Do not use Optional in method args
- 240. Do not use Optional to return empty or null collections or arrays
- 241. Avoiding Optional in collections
- 242. Confusing of() with ofNullable()
- 243. Optional<T> versus OptionalInt
- 244. Asserting equality of Optionals
- 245. Transforming values via Map() and flatMap()
- 246. Filter values via Optional.filter()
- 247. Chaining the Optional and Stream APIs
- 248. Optional and identity-sensitive operations
- 249. Returning a boolean if the Optional class is empty
- Summary
- The HTTP Client and WebSocket APIs
- Problems
- Solutions
- 250. HTTP/2
- 251. Triggering an asynchronous GET request
- 252. Setting a proxy
- 253. Setting/getting headers
- 254. Specifying the HTTP method
- 255. Setting a request body
- 256. Setting connection authentication
- 257. Setting a timeout
- 258. Setting the redirect policy
- 259. Sending sync and async requests
- 260. Handling cookies
- 261. Getting response information
- 262. Handling response body types
- 263. Getting, updating, and saving a JSON
- 264. Compression
- 265. Handling form data
- 266. Downloading a resource
- 267. Uploading with multipart
- 268. HTTP/2 server push
- 269. WebSocket
- Summary
- Other Books You May Enjoy
Averaging
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