@ohos.util.LightWeightMap (Nonlinear Container LightWeightMap)

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. Its default initial capacity is 8, and it has the capacity doubled in each expansion.

The keys in such a set 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.

This topic uses the following to identify the use of generics:

• K: Key
• V: Value

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.

Modules to Import

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

LightWeightMap

Attributes

System capability: SystemCapability.Utils.Lang

constructor

constructor()

A constructor used to create a LightWeightMap instance.

System capability: SystemCapability.Utils.Lang

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();

isEmpty

isEmpty(): boolean

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

const lightWeightMap: LightWeightMap<string, number> = 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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let map: LightWeightMap<string, number> = new LightWeightMap();
map.set("sparrow", 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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
let result = lightWeightMap.hasKey("squirrel");

hasValue

hasValue(value: V): boolean

Checks whether this container contains the specified value.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
let result = lightWeightMap.hasValue(123);

increaseCapacityTo

increaseCapacityTo(minimumCapacity: number): void

Increases the capacity of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = 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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.get("sparrow");

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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.getIndexOfKey("sparrow");

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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let map: LightWeightMap<string, number> = new LightWeightMap();
map.setAll(lightWeightMap); // Add all elements in lightWeightMap to the map.

set

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

Adds or updates an element in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
let result = lightWeightMap.set("squirrel", 123);

remove

remove(key: K): V

Removes an element with the specified key from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
lightWeightMap.remove("sparrow");

removeAt

removeAt(index: number): boolean

Removes an element at the specified position from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.getValueAt(1);

clear

clear(): void

Clears this container and sets its length to 0.

System capability: SystemCapability.Utils.Lang

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let iter = lightWeightMap.keys();
let temp: IteratorResult<string, number> = iter.next();
while(!temp.done) {
  console.log("value:" + temp.value);
  temp = iter.next();
}

values

values(): IterableIterator<V>

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let iter = lightWeightMap.values();
let temp: IteratorResult<number> = iter.next();
while(!temp.done) {
  console.log("value:" + temp.value);
  temp = iter.next();
}

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

callbackFn

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("sparrow", 123);
lightWeightMap.set("gull", 357);
lightWeightMap.forEach((value?: number, key?: string) => {
  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

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let iter = lightWeightMap.entries();
let temp: IteratorResult<Object[]> = iter.next();
while(!temp.done) {
  console.log("key:" + temp.value[0]);
  console.log("value:" + temp.value[1]);
  temp = iter.next();
}

toString

toString(): String

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.toString();

[Symbol.iterator]

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

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

NOTE

This API cannot be used in .ets files.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);

// Method 1:
let nums = Array.from(lightWeightMap.values());
for (let item1 of nums) {
  console.log("value:" + item1);
}

let key = Array.from(lightWeightMap.keys());
for (let item2 of key) {
  console.log("key:" + item2);
}

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