essentials4j - the perfect library for every Java 8 project!

Essentials4j is a minimalistic library consisting of:

• a thin layer of abstraction over Java 8 streams for easy manipulation of collections,
• simple factory utils for elegant construction of collections.

Java 8 streams are powerful, and essentials4j is just a fantastic way to use them!

Example

Map<Integer, String> nums = New.map(1, "one", 2, "two", 3, "three");
Map<Integer, String> even = Do.findIn(nums).all((k, v) -> k % 2 == 0); // {2:"two"}

The code above is a shortcut for:

Map<Integer, String> nums = newLinkedHashMap<>();
nums.put(1, "one");
nums.put(2, "two");
nums.put(3, "three");
Map<Integer, String> even = nums.entrySet().stream()
.filter(entry -> entry.getKey() % 2 == 0)
.collect(Collectors.toMap(Entry::getKey, Entry::getValue)); // {2:"two"}

Features

What makes essentials4j perfect?

• Simple, elegant & straight to the point
• 100% test coverage
• 100% documentation coverage
• Open-source (Apache Public License v2)
• Lightweight (consists of only 9 classes)
• Self-contained (no dependencies)
• Only 15 KB JAR size

Usage

Maven dependency

 <dependency>
<groupId>org.essentials4j</groupId>
<artifactId>essentials4j</artifactId>
<version>1.0.0</version>
</dependency>

API

Instantiation:

List<E> list = New.list(...)
Set<E> set = New.set(...)
Map<K,V> map = New.map(...)

Searching:

List<E> results = Do.findIn(items).all(predicate)
Optional<E> any = Do.findIn(items).any(predicate)
Optional<E> first = Do.findIn(items).first(predicate)
Optional<E> last = Do.findIn(items).last(predicate)
booleanexists = Do.findIn(items).exists(predicate)

Transforming:

List<E> list = Do.map(items).toList(transformation)
List<E> set = Do.map(items).toSet(transformation)
Map<K,V> map = Do.map(items).toMap(keyTransformation, valueTransformation)

Grouping by classifier:

Map<T, List<E>> groups = Do.group(collection).by(classifier)
Map<T, Map<K,V>> groups = Do.group(map).by(classifier)

Examples: searching through collections

Let's search through this list of items in the following examples:

List<String> abc = New.list("a", "bbb", "cc");

Find all:

List<String> words = Do.findIn(abc).all(s -> s.length() > 1); // ["bbb", "cc"]

Find any:

Optional<String> anyLetter = Do.findIn(abc).any(s -> s.length() == 1); // "a"

Find first:

Optional<String> firstWord = Do.findIn(abc).first(s -> s.length() > 1); // "bbb"

Find last:

Optional<String> lastWord = Do.findIn(abc).last(s -> s.length() > 1); // "cc"

Exists:

booleanhasLetter = Do.findIn(abc).exists(s -> s.length() == 1) // true

Examples: mapping and grouping collections

Let's transform this list of items in the following examples:

List<String> abc = New.list("a", "bb", "cc");

Mapping to a List:

List<Integer> lengths = Do.map(abc).toList(String::length); // [1, 2, 2]

Mapping to a Set:

Set<Integer> lengths2 = Do.map(abc).toSet(String::length); // [1, 2]

Mapping to a Map:

Map<String, Integer> lengths3 = Do.map(abc).toMap(s -> s, String::length); // {"a":1, "bb":2, "cc":2}

Group by:

Map<Integer, List<String>> byLength = Do.group(abc).by(String::length); // {1:["a"], 2:["bb", "cc"]}

Examples: searching through maps

Let's search through this map of items in the following examples:

Map<Integer, String> nums = New.map(-1, "neg", 0, "zero", 1, "pos");

Find all:

Map<Integer, String> notNegative = Do.findIn(nums).all((k, v) -> k >= 0); // {0:"zero", 1:"pos"}

Find any:

Optional<Entry<Integer, String>> anyPositive = Do.findIn(nums).any((k, v) -> k > 0); // 1:"pos"

Find first:

Optional<Entry<Integer, String>> firstNonZero = Do.findIn(nums).first((k, v) -> k != 0); // -1:"neg"

Find last:

Optional<Entry<Integer, String>> lastNonZero = Do.findIn(nums).last((k, v) -> k != 0); // 1:"pos"

Exists:

booleanhasPositive = Do.findIn(nums).exists((k, v) -> k > 0); // true

Examples: mapping and grouping maps

Let's transform this map of items in the following examples:

Map<Integer, String> nums = New.map(1, "one", 2, "two", 3, "three");

Mapping to a List:

List<Integer> squared = Do.map(nums).toList((k, v) -> k * k); // [1, 4, 9]

Mapping to a Set:

Set<Integer> wordLengths = Do.map(nums).toSet((k, v) -> v.length()); // [3, 5]

Mapping to a Map:

// {1000:"ONE", 2000:"TWO", 3000:"THREE"}Map<Integer, String> thousands = Do.map(nums).toMap((k, v) -> k * 1000, (k, v) -> v.toUpperCase());

Group by:

// { false: {1:"one", 3:"three"}, true: {2:two} }Map<Boolean, Map<Integer, String>> even = Do.group(nums).by((k, v) -> k % 2 == 0);