Nonlinear Container LightWeightMap

NOTE

The initial APIs of this module are supported since API version 8. Newly added APIs will be marked with a superscript to indicate their earliest API version.

LightWeightMap stores key-value (KV) pairs. Each key must be unique and have only one value.

LightWeightMap is based on generics and uses a lightweight structure. Keys in the map are searched using hash values, which are stored in an array.

Compared with HashMap, which can also store KV pairs, LightWeightMap occupies less memory.

Recommended use case: Use LightWeightMap when you need to store and access KV pairs.

Modules to Import

import LightWeightMap from '@ohos.util.LightWeightMap';

LightWeightMap

Attributes

System capability: SystemCapability.Utils.Lang

Name	Type	Readable	Writable	Description
length	number	Yes	No	Number of elements in a lightweight map (called container later).

constructor

constructor()

A constructor used to create a LightWeightMap instance.

System capability: SystemCapability.Utils.Lang

Example

let lightWeightMap = new LightWeightMap();

isEmpty

isEmpty(): boolean

Checks whether this container is empty (contains no element).

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
boolean	Returns true if the container is empty; returns false otherwise.

Example

const lightWeightMap = new LightWeightMap();
let result = lightWeightMap.isEmpty();

hasAll

hasAll(map: LightWeightMap<K, V>): boolean

Checks whether this container contains all elements of the specified LightWeightMap instance.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
map	LightWeightMap<K, V>	Yes	LightWeightMap instance to be used for comparison.

Return value

Type	Description
boolean	Returns true if all the elements in the specified LightWeightMap instance are contained; returns false otherwise.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let map = new LightWeightMap();
map.set("sdfs", 356);
let result = lightWeightMap.hasAll(map);

hasKey

hasKey(key: K): boolean;

Checks whether this container contains the specified key.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Target key.

Return value

Type	Description
boolean	Returns true if the specified key is contained; returns false otherwise.

Example

let lightWeightMap = new LightWeightMap();
let result = lightWeightMap.hasKey;
lightWeightMap.hasKey("Ahfbrgrbgnutfodgorrogorgrogofdfdf");
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
let result1 = lightWeightMap.hasKey("Ahfbrgrbgnutfodgorrogorgrogofdfdf");

hasValue

hasValue(value: V): boolean

Checks whether this container contains the specified value.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
value	V	Yes	Target value.

Return value

Type	Description
boolean	Returns true if the specified value is contained; returns false otherwise.

Example

let lightWeightMap = new LightWeightMap();
let result = lightWeightMap.hasValue(123);
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
let result1 = lightWeightMap.hasValue(123);

increaseCapacityTo

increaseCapacityTo(minimumCapacity: number): void

Increases the capacity of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
minimumCapacity	number	Yes	Minimum number of elements to accommodate in this container.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.increaseCapacityTo(10);

get

get(key: K): V

Obtains the value of the specified key in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Target key.

Return value

Type	Description
V	Value of the key.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.get("sdfs");

getIndexOfKey

getIndexOfKey(key: K): number

Obtains the index of the first occurrence of an element with the specified key in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Key of the element.

Return value

Type	Description
number	Returns the position index if obtained; returns -1 otherwise.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getIndexOfKey("sdfs");

getIndexOfValue

getIndexOfValue(value: V): number

Obtains the index of the first occurrence of an element with the specified value in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
value	V	Yes	Key of the element.

Return value

Type	Description
number	Returns the position index if obtained; returns -1 otherwise.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getIndexOfValue(123);

getKeyAt

getKeyAt(index: number): K

Obtains the key of an element at the specified position in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element.

Return value

Type	Description
K	Returns the key if obtained; returns undefined otherwise.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getKeyAt(1);

setAll

setAll(map: LightWeightMap<K, V>): void

Adds all elements in a LightWeightMap instance to this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
map	LightWeightMap<K, V>	Yes	LightWeightMap instance whose elements are to be added to the current container.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let map = new LightWeightMap();
lightWeightMap.setAll(map);

set

set(key: K, value: V): Object

Adds an element to this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Key of the target element.
value	V	Yes	Value of the target element.

Return value

Type	Description
Object	Container that contains the new element.

Example

let lightWeightMap = new LightWeightMap();
let result = lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);

remove

remove(key: K): V

Removes an element with the specified key from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Target key.

Return value

Type	Description
V	Value of the element removed.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
lightWeightMap.remove("sdfs");

removeAt

removeAt(index: number): boolean

Removes an element at the specified position from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element.

Return value

Type	Description
boolean	Returns true if the element is removed successfully; returns false otherwise.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.removeAt(1);

setValueAt

setValueAt(index: number, newValue: V): boolean

Sets a value for an element at the specified position in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the target element.
newValue	V	Yes	Value of the target element to set.

Return value

Type	Description
boolean	Returns true if the value is set successfully; returns false otherwise.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
lightWeightMap.setValueAt(1, 3546);

getValueAt

getValueAt(index: number): V

Obtains the value of an element at the specified position in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element.

Return value

Type	Description
V	Value obtained.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getValueAt(1);

clear

clear(): void

Clears this container and sets its length to 0.

System capability: SystemCapability.Utils.Lang

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
lightWeightMap.clear();

keys

keys(): IterableIterator<K>

Obtains an iterator that contains all the keys in this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<K>	Iterator obtained.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.keys();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("value:" + temp);
  temp = iter.next().value;
}

values

values(): IterableIterator<V>

Obtains an iterator that contains all the values in this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<V>	Iterator obtained.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.values();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("value:" + temp);
  temp = iter.next().value;
}

forEach

forEach(callbackfn: (value?: V, key?: K, map?: LightWeightMap<K, V>) => void, thisArg?: Object): void

Uses a callback to traverse the elements in this container and obtain their position indexes.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
callbackfn	function	Yes	Callback invoked to traverse the elements in the container.
thisArg	Object	No	Value to use when the callback is invoked.

callbackfn

Name	Type	Mandatory	Description
value	V	No	Value of the element that is currently traversed.
key	K	No	Key of the element that is currently traversed.
map	LightWeightMap<K, V>	No	Instance that invokes the forEach method.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("sdfs", 123);
lightWeightMap.set("dfsghsf", 357);
lightWeightMap.forEach((value, key) => {
    console.log("value:" + value, "key:" + key);
});

entries

entries(): IterableIterator<[K, V]>

Obtains an iterator that contains all the elements in this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<[K, V]>	Iterator obtained.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.entries();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("key:" + temp[0]);
  console.log("value:" + temp[1]);
  temp = iter.next().value;
}

toString

toString(): String

Concatenates the elements in this container into a string and returns the string.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
String	String obtained.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("A", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.toString();

[Symbol.iterator]

[Symbol.iterator](): IterableIterator<[K, V]>

Obtains an iterator, each item of which is a JavaScript object.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<[K, V]>	Iterator obtained.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);

// Method 1:
for (let item of lightWeightMap) { 
  console.log("key:" + item[0]);
  console.log("value:" + item[1]);
}

// Method 2:
let iter = lightWeightMap[Symbol.iterator]();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("key:" + temp[0]);
  console.log("value:" + temp[1]);
  temp = iter.next().value;
}