Comparator<T> class abstract

An abstract class that imposes a total ordering on a collection of objects of type T.

A Comparator can be used to:

  • Sort lists (List.sort(comparator)).
  • Control ordering in sorted collections (e.g., custom trees or ordered maps).
  • Provide alternate sort logic for types that don’t implement Comparable.

This Dart class is inspired by Java's java.util.Comparator.

πŸ“Œ Example Usage

final Comparator<String> byLength = Comparator.comparing((s) => s.length);

final names = ['Alice', 'Bob', 'Christina'];
names.sort(byLength.compare);

print(names); // [Bob, Alice, Christina]

You can also chain comparators:

final byLengthThenAlphabet = Comparator.comparing((s) => s.length)
    .thenComparing(Comparator.naturalOrder());

final list = ['Tom', 'Ann', 'Tim', 'Jim', 'Alex'];
list.sort(byLengthThenAlphabet.compare);

print(list); // [Ann, Jim, Tom, Tim, Alex]
Implementers
Annotations

Constructors

Comparator()
An abstract class that imposes a total ordering on a collection of objects of type T.
const

Properties

hashCode β†’ int
The hash code for this object.
no setterinherited
runtimeType β†’ Type
A representation of the runtime type of the object.
no setterinherited

Methods

compare(T a, T b) β†’ int
Compares two values of type T for order.
noSuchMethod(Invocation invocation) β†’ dynamic
Invoked when a nonexistent method or property is accessed.
inherited
reversed() β†’ Comparator<T>
Returns a comparator that imposes the reverse ordering of this comparator.
thenComparing(Comparator<T> other) β†’ Comparator<T>
Chains another comparator to be used if this comparator returns 0 (equality).
thenComparingComparable<U extends Comparable<U>>(U keyExtractor(T)) β†’ Comparator<T>
Chains a comparator by extracting a Comparable key from each element.
thenComparingWith<U>(U keyExtractor(T), Comparator<U> keyComparator) β†’ Comparator<T>
Chains a comparator by extracting a key with keyExtractor and comparing it using the given keyComparator.
toString() β†’ String
A string representation of this object.
inherited

Operators

operator ==(Object other) β†’ bool
The equality operator.
inherited

Static Methods

comparing<T, U extends Comparable<U>>(U keyExtractor(T)) β†’ Comparator<T>
Creates a comparator based on a Comparable key extracted from each element.
comparingWith<T, U>(U keyExtractor(T), Comparator<U> keyComparator) β†’ Comparator<T>
Creates a comparator based on a key extractor and a custom comparator for the key.
naturalOrder<T>() β†’ Comparator<T>
Creates a comparator that compares Comparable objects in natural ascending order.
reverseOrder<T>() β†’ Comparator<T>
Creates a comparator that compares Comparable objects in reverse (descending) order.