[JAVA] Eclipse Collections cheat sheet

Overview

As for the explanation of Eclipse Collections itself, I think there are many other good articles, so here I will upload it as a reference that you can refer to immediately when you think "I want to do XX". For the time being, I've listed the ones I use most often, but I may add them if they come out.

• • Almost only List type is written. *

environment

Ver.8.0.0

• I'm sorry, it's a version that I usually use at work, so it's a little old. *

pom.xml

		<dependency>
			<groupId>org.eclipse.collections</groupId>
			<artifactId>eclipse-collections-api</artifactId>
			<version>8.0.0</version>
		</dependency>
		<dependency>
			<groupId>org.eclipse.collections</groupId>
			<artifactId>eclipse-collections</artifactId>
			<version>8.0.0</version>
		</dependency>

Initialization

Empty list

empty

Lists.mutable.empty();

From this point onward, immutable (ImmutableList) can be used in addition to mutable (MutableList), unless otherwise specified. ImmutableList does not have methods such as add and cannot be changed.

• • Please note that there are some methods such as sort that can only be used with MutableList *

empty

Lists.immutable.empty();

Initialize all together

of

Lists.mutable.of(first, second, third);

Initialize based on Iterable

You can convert java.util.List etc. to ImmutableList etc.

ofall

Lists.immutable.ofAll(hogeList);

Frequent pattern collection

Extract only elements that satisfy the conditions

select

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList
					.select(s -> s.contains("g"))
					.makeString()
				, is("hoge, fuga")
			);

I want to check if there is an element that meets the conditions

ʻAnySatisfy` returns true if there is at least one element that meets the condition.

anySatisfy

		ListIterable<String> hogeList = Lists.mutable.of("hoge", null, "fuga");
		assertThat(
				hogeList.anySatisfy(s -> s == null)
				, is(true)
			);

I want to make sure that all the elements do not meet the conditions

noneSatisfy returns true if there are no elements that meet the condition.

noneSatisfy

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList.noneSatisfy(s -> s.equals("hogera"))
				, is(true)
			);

I want to get if there is even one element that meets the conditions

detect retrieves only the first one of the elements that meet the condition.

detect

		ListIterable<String> hogeList = Lists.mutable.of(null, "hoge", "fuga");
		assertThat(
				hogeList.detect(s -> s != null).toString()
				, is("hoge")
			);

Convert the element to a new List

collect

		ListIterable<String> hogeList = Lists.mutable.of("hogehoge", "fuga", "piyopi");
		assertThat(
				hogeList
					.collect(s -> s.length())
					.makeString()
				, is("8, 4, 6")
			);

Deduplication

Eliminate duplication and leave only unique elements.

distinct

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo", "fuga", "piyo");
		assertThat(
				hogeList
					.distinct()
					.makeString()
				, is("hoge, fuga, piyo")
			);

It is also possible to specify the criteria to judge that it is unique. At this time, only the first one of the duplicate elements remains in the list of results.

distinct

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo", "fugafuga", "piyopiyo");
		assertThat(
				hogeList
					.distinct(HashingStrategies.fromFunction(s -> s.length()))
					.makeString()
				, is("hoge, fugafuga")
			);

Sorting

sortThis

		MutableList<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList
					.sortThis()
					.makeString()
				, is("fuga, hoge, piyo")
			);

It is also possible to specify the sorting criteria and to sort in descending order.

sortThisBy

		MutableList<String> hogeList = Lists.mutable.of("hogehoge", "fuga", "piyopi");
		assertThat(
				hogeList
					.sortThisBy(s -> s.length())
					.reverseThis()
					.makeString()
				, is("hogehoge, piyopi, fuga")
			);

repetition

If you want to repeat the process and then continue writing, there is also tap.

each

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		hogeList
			.each(s ->
				System.out.println(s)
			);
		//Execution result
		//hoge
		//fuga
		//piyo

With forEachWithIndex, you can loop with index.

forEachWithIndex

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		hogeList
			.forEachWithIndex((string, index) ->
				System.out.println(String.valueOf(index).concat(string))
			);
		//Execution result
		//0hoge
		//1fuga
		//2piyo

Aggregate

With groupBy, you can group by the specified value. It comes back in the type ListMultimap and can be retrieved in various ways, but I like to use it as Pair (discussed below) with the keyMultiValuePairsView () method.

groupBy

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "hogera", "fuga", "fugafuga", "piyo", "piyopiyo");
		hogeList
			.groupBy(s -> s.length())
			.keyMultiValuePairsView()
			.each(p ->{
				System.out.println(p.getOne() + " -> " + p.getTwo());
			});
		//Execution result
		//4 -> [hoge, fuga, piyo]
		//6 -> [hogera]
		//8 -> [fugafuga, piyopiyo]

total

sumOfInt

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList
					.sumOfInt(s -> s.length())
				, is(12L)
			);

I want to get only one element

First one

If there are no elements, null is returned.

getFirst

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList
					.select(s -> s.contains("g"))
					.getFirst()
				, is("hoge")
			);

Last one

Again, null is returned if there are no elements.

getLast

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList
					.select(s -> s.contains("g"))
					.getLast()
				, is("fuga")
			);

Element that should be only one

If you should be able to narrow down the elements to only one with select etc., use getOnly. IllegalStateException is thrown if there is more than one element.

getOnly

		ListIterable<String> hogeList = Lists.mutable.of("hoge", "fuga", "piyo");
		assertThat(
				hogeList
					.select(s -> s.contains("i"))
					.getOnly()
				, is("piyo")
			);

Conversion from standard collection

The frameworks used in the project often use standard collections such as java.util.List. In such a case, if you want to use Eclipse Collections, you will have to convert it to the Eclipse Collections type once with ʻofAll` etc. as shown below, but it will be a little disturbing if the number increases.

Tend to be like this

List<String> hogeList = Arrays.asList("konna", "fuuni", "shiteita");
ImmutableList<String> fugaList = Lists.immutable.ofAll(hogeList);
fugaList.select(s -> s.length > 4);

In such a case, you can use the method of eclipse collestions in one shot by using ListAdapter. If it's ʻArray instead of List, there's also ʻArrayAdapter.

This was good

List<String> hogeList = Arrays.asList("kore", "de", "yokatta");
ListAdapter.adapt(hogeList)
           .select(s -> s.length > 4);

There are also ListIterate and ʻArrayIterate` that don't even require adapt.

ListIterate

List<String> hogeList = Arrays.asList("adapt", "mo", "shinai");
ListIterate.select(hogeList, s -> s.length > 4);

Other datasets

I want to keep two values as a set

It is used when you want to have data as a pair of key and value. Two types of instances can be created from Tuples. Pair<T1, T2> Click here for different types.

Pair

Pair<String, Object> keyValuePair = Tuples.pair("key", value);
String key = keyValuePair.getOne();
Object value = keyValuePair.getTwo();

Twin If you want to work with values of the same type, you can use this.

Twin

Twin<String> keyValueTwin = Tuples.twin("key", "valiue");
String key = keyValueTwin.getOne();
String value = keyValueTwin.getTwo();

Exception handling

If a check exception occurs in lambda, the code that was written concisely will be ruined. In such a case, statically import the following and use the throwing method.

import static org.eclipse.collections.impl.block.factory.Procedures.*;
import static org.eclipse.collections.impl.block.factory.Functions.*;
import static org.eclipse.collections.impl.block.factory.Predicates.*;

If an exception occurs during throwing, it will wrap it in a RuntimeException and throw it again. Now I can write it concisely.

throwing

		hogeList
			.each(throwing(Fuga::piyo)
			;