SplayTreeMap<K, V> class Null safety

A Map of objects that can be ordered relative to each other.

The map is based on a self-balancing binary tree. It allows most single-entry operations in amortized logarithmic time.

Keys of the map are compared using the compare function passed in the constructor, both for ordering and for equality. If the map contains only the key a, then map.containsKey(b) will return true if and only if compare(a, b) == 0, and the value of a == b is not even checked. If the compare function is omitted, the objects are assumed to be Comparable, and are compared using their Comparable.compareTo method. Non-comparable objects (including null) will not work as keys in that case.

To allow calling operator [], remove or containsKey with objects that are not supported by the compare function, an extra isValidKey predicate function can be supplied. This function is tested before using the compare function on an argument value that may not be a K value. If omitted, the isValidKey function defaults to testing if the value is a K.

Notice: Do not modify a map (add or remove keys) while an operation is being performed on that map, for example in functions called during a forEach or putIfAbsent call, or while iterating the map (keys, values or entries).

Example:

final planetsByMass = SplayTreeMap<double, String>((a, b) => a.compareTo(b));

To add data to a map, use operator[]=, addAll or addEntries.

planetsByMass[0.06] = 'Mercury';
planetsByMass
    .addAll({0.81: 'Venus', 1.0: 'Earth', 0.11: 'Mars', 317.83: 'Jupiter'});

To check if the map is empty, use isEmpty or isNotEmpty. To find the number of map entries, use length.

print(planetsByMass.isEmpty); // false
print(planetsByMass.length); // 5

The forEach method calls a function for each key/value entry of the map.

planetsByMass.forEach((key, value) {
  print('$key \t $value');
  // 0.06    Mercury
  // 0.11    Mars
  // 0.81    Venus
  // 1.0     Earth
  // 317.83  Jupiter
});

To check whether the map has an entry with a specific key, use containsKey.

final keyOneExists = planetsByMass.containsKey(1.0); // true
final keyFiveExists = planetsByMass.containsKey(5); // false

To check whether the map has an entry with a specific value, use containsValue.

final earthExists = planetsByMass.containsValue('Earth'); // true
final plutoExists = planetsByMass.containsValue('Pluto'); // false

To remove an entry with a specific key, use remove.

final removedValue = planetsByMass.remove(1.0);
print(removedValue); // Earth

To remove multiple entries at the same time, based on their keys and values, use removeWhere.

planetsByMass.removeWhere((key, value) => key <= 1);
print(planetsByMass); // {317.83: Jupiter}

To conditionally add or modify a value for a specific key, depending on whether there already is an entry with that key, use putIfAbsent or update.

planetsByMass.update(1, (v) => '', ifAbsent: () => 'Earth');
planetsByMass.putIfAbsent(317.83, () => 'Another Jupiter');
print(planetsByMass); // {1.0: Earth, 317.83: Jupiter}

To update the values of all keys, based on the existing key and value, use updateAll.

planetsByMass.updateAll((key, value) => 'X');
print(planetsByMass); // {1.0: X, 317.83: X}

To remove all entries and empty the map, use clear.

planetsByMass.clear();
print(planetsByMass.isEmpty); // false
print(planetsByMass); // {}

See also:

• Map, the general interface of key/value pair collections.
• HashMap is unordered (the order of iteration is not guaranteed).
• LinkedHashMap iterates in key insertion order.