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Add Comparator factories and fluent ordering pattern #197

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Merged
brunoborges merged 1 commit into from
Aug 26, 2026
+69 −1
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Add Comparator factories and fluent ordering pattern #197

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2 changes: 1 addition & 1 deletion content/collections/collection-bulk-operations.yaml
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ support:
state: "available"
description: "Available since JDK 8 (March 2014)"
prev: "collections/stack-to-deque"
next: null
next: "collections/comparator-factories"
related:
- "collections/reverse-list-iteration"
- "collections/copying-collections-immutably"
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51 changes: 51 additions & 0 deletions content/collections/comparator-factories.yaml
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@@ -0,0 +1,51 @@
---
id: a1ac8e52-14cf-49be-a22a-be72de7caa4e
slug: "comparator-factories"
title: "Comparator factories and fluent ordering"
category: "collections"
difficulty: "beginner"
jdkVersion: "8"
oldLabel: "Anonymous comparator"
modernLabel: "Java 8+"
oldApproach: "Anonymous Comparator"
modernApproach: "Comparator factories"
oldCode: |-
people.sort(new Comparator<Person>() {
@Override
public int compare(Person a, Person b) {
int byName = a.name().compareTo(b.name());
return byName != 0 ? byName : Integer.compare(a.age(), b.age());
}
});
modernCode: |-
people.sort(Comparator.comparing(Person::name)
.thenComparingInt(Person::age));
summary: "Build readable, composable ordering rules with Comparator factory methods."
explanation: "Comparator factories express ordering declaratively and compose primary and secondary keys without handwritten branching."
whyModernWins:
- icon: "🧩"
title: "Composable"
desc: "Ordering rules chain naturally."
- icon: "👁"
title: "Easier to review"
desc: "Sort keys and priority are explicit."
- icon: "🐛"
title: "Safer comparisons"
desc: "Specialized helpers avoid error-prone arithmetic comparators."
support:
state: "available"
description: "Available since JDK 8 (March 2014)"
prev: "collections/collection-bulk-operations"
next: null
related:
- "collections/collection-bulk-operations"
- "collections/reverse-list-iteration"
- "language/static-methods-in-interfaces"
tags:
- collections
- functional
docs:
- title: "Comparator.comparing()"
href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Comparator.html#comparing(java.util.function.Function)"
- title: "Comparator.thenComparingInt()"
href: "https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/util/Comparator.html#thenComparingInt(java.util.function.ToIntFunction)"
17 changes: 17 additions & 0 deletions proof/collections/ComparatorFactories.java
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@@ -0,0 +1,17 @@
///usr/bin/env jbang "$0" "$@" ; exit $?
//JAVA 25+
import java.util.*;

/// Proof: comparator-factories
/// Source: content/collections/comparator-factories.yaml
void main() {
record Person(String name, int age) {}

var people = new ArrayList<>(List.of(
new Person("Ada", 36),
new Person("Ada", 28),
new Person("Grace", 40)));

people.sort(Comparator.comparing(Person::name)
.thenComparingInt(Person::age));
}