Java 8 Stream & C# 3.5

Trần Duy Quang – May 2014

Agenda

1. Some notable new things in Java 8

2. Comparison with LINQ in C# 3.5!

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1

Some new things in Java 8

Notable things

Lambda expressions

Default methods

Method reference

Stream

Optional

New Date & Time API

Functional programming

Reference (blog post): Everything about Java 84

Lambda expression

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(x, y) -> x + y

Passing function around

Dynamically (usually weakly) typed: Javascript

Strongly typed: Ruby, Scala, Closure

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Functional approach

Concise UsefulParalellizable

Why lambda in Java now?

Clearer than anonymous inner class

Basic for stream library

shapes.forEach(s -> s.setColor(Color.RED));

A step toward functional programming !

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Main advantage of lambdas

Concise & expressive

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New way of thinking

Encourage functional programming

Many classes of problems are easier to solve

Code is clearer to read, simpler to maintain

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What we actually get?

An instance of a class that implements the

interface that was expected in that place

Remember this?

Interface that has exactly one abstract method!

Functional Interface | Single Abstract Method

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Shortening lambda syntax

Omit parameter types

Expressions instead of blocks

Single arguments? Omit parenthesis!

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Even better with high-order function

High-order function: method return lambdas

comparing method of Comparator need function

specifying how to extract the key

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Method reference

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Core idea behind

Make lambda more succinct!

Rather than

angles.map(x -> Math.sin(x));

Can be shorthand

angles.map(Math::sin);

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Predicate

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Core idea behind

Boolean test(T t)

A function to test condition

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Benefit: Flexibility

Even better with stream (later slides)

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Similar things

Predicate: boolean test(T t)

Check a condition

Consumer: void consume(T t)

Perform action with the given object

BiConsumer: with two parameters

Function: R change(T t)

Take an object type T and return new object type R

BiFunction: with two parameters

Supplier: T supply(T t)

Return an object with the same type

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More convenient helper classes

IntConsumer

IntFunction<R>

IntPredicate

IntSupplier

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Stream

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Stream

Wrapper around data sources: arrays, collections…

Use lambdas

Support map/reduce

Lazy evaluation

Made parallel atutomatically by compiler

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Making streams

From individual values Stream.of(val1, val2,…)

From array Stream.of(names), Arrays.stream(names)

From List (and other collections) names.stream()

From a StreamBuilder builder.build()

From String String.chars, Arrays.stream(s.split())

From another stream distinct, filter, map, limit, sorted, substream

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Turn stream to other data structures

Array

employees.toArray(Employee[]::new);

List

names.collect(Collectors.toList());

Set

names.collect(Collectors.toSet());

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2

Comparison with LINQ in C#

Restriction Operators

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1. Filtering

Find names where “am” occurs

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2. Indexed Filtering (tricky)

Find names where length <= index + 1

(generate an indexed stream out of the original array)

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Projection Operators

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3. Selecting/Mapping

Add “Hello “ in front of each names

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4. Selecting Many/Flattening

Project all the elements in a single collection

Java: Transform to entry set, then flatten

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Partitioning Operators

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5. Taking an Arbitrary Number of Items

Obtain the first 4 items

Java: convert IntStream into Stream<Integer>

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6. Taking Items Based on Predicate

Take while having the string that start with “S”

Java: don’t have the short-circuited ability, have to

create Boolean map

33Different meaning from the above!

7. Skipping an Arbitrary Number of Items

Skip top items, take the rest

Java:

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8. Skipping Items Based on Predicate

LINQ: SkipWhile

Sadly, no way in Java

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Ordering Operators

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9. Ordering/Sorting Elements

Order the elements of a collection alphabetically

Java:

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10. Ordering/Sorting Elements by

Specific Criterium

Ordering by the length of the string

Java

Shorthand:

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11. Ordering/Sorting Elements by

Multiple Criteria

Sort by length, then by order

Java:

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Grouping Operators

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12.Grouping by a Criterium

Group collection of strings by their length

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Set Operators

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13. Filter Distinct Elements

Obtain all the distinct elements from a collection

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14. Union of Two Sets

Join together two sets of items

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Element Operatos

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15. First Element

Obtain the first element of a collection

Java: Maybe better!

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Range Operators

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16. Generate a Range of Numbers

Generate a range of no that are multiples of 11

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Quantifier Operators

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17. All

Do all elements in a collection satisfy a predicate?

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18. Any

Do any elements in a collection satisfy a predicate?

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Merging Operators

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19.Zip

Combine two collections into a single collection

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The last coffee drop

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Still left behind by C#! Gambatte, Java!

Make IntelliJ IDEA work with Java 8

Make sure you have the latest version (>=13.1.2)

Change project language level to 8.0 (F4)

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Reference

Blog post: Java Streams Preview vs .Net High-

Order Programming with LINQ

Slide: Evolution of Java

Slide: Lambda expressions & Stream in Java 8

Slide: Java 8 Stream Tutorial Part 1

Slide: Java 8 Stream Tutorial part 2

Just for fun (Youtube Video 20”):

Javapocalypse ^^

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