@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 '@kit.ArkTS';

LightWeightMap

Attributes

Atomic service API: This API can be used in atomic services since API version 12.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Error codes

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

ID	Error Message
10200012	The LightWeightMap's constructor cannot be directly invoked.

Example

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

isEmpty

isEmpty(): boolean

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

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

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

Error codes

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

ID	Error Message
10200011	The isEmpty method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types.
10200011	The hasAll method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
10200011	The hasKey method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
10200011	The hasValue method cannot be bound.

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.

If the passed-in capacity is greater than or equal to the number of elements in this container, the container capacity is changed to the new capacity. If the passed-in capacity is less than the number of elements in this container, the capacity is not changed.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

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

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types.
10200011	The increaseCapacityTo method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Target key.

Return value

Type	Description
V	Value of the key.

Error codes

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

ID	Error Message
10200011	The get method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
10200011	The getIndexOfKey method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
10200011	The getIndexOfValue method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element. The value must be less than or equal to int32_max, that is, 2147483647.

Return value

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

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types; 3. Parameter verification failed.
10200001	The value of index is out of range.
10200011	The getKeyAt method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types.
10200011	The setAll method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
10200011	The set method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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.

Error codes

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

ID	Error Message
10200011	The remove method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element. The value must be less than or equal to int32_max, that is, 2147483647.

Return value

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

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types.
10200011	The removeAt method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element. The value must be less than or equal to int32_max, that is, 2147483647.
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.

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types; 3. Parameter verification failed.
10200001	The value of index is out of range.
10200011	The setValueAt method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
index	number	Yes	Position index of the element. The value must be less than or equal to int32_max, that is, 2147483647.

Return value

Type	Description
V	Value obtained.

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types; 3. Parameter verification failed.
10200001	The value of index is out of range.
10200011	The getValueAt method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Error codes

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

ID	Error Message
10200011	The clear method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<K>	Iterator obtained.

Error codes

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

ID	Error Message
10200011	The keys method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<V>	Iterator obtained.

Error codes

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

ID	Error Message
10200011	The values method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

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 of this to use when callbackFn is invoked. The default value is this instance.

callbackFn

Name	Type	Mandatory	Description
value	V	No	Value of the element that is currently traversed. The default value is the value of the first key-value pair.
key	K	No	Key of the element that is currently traversed. The default value is the key of the first key-value pair.
map	LightWeightMap<K, V>	No	Instance that calls the forEach API. The default value is this instance.

Error codes

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

ID	Error Message
401	Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types.
10200011	The forEach method cannot be bound.

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);
});

// You are not advised to use the set, setValueAt, remove, or removeAt APIs in forEach because they may cause unpredictable risks such as infinite loops. You can use the for loop when inserting or deleting data.
let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
for(let i = 0; i < 10; i++) {
  lightWeightMap.set("sparrow" + i, 123);
}
for(let i = 0; i < 10; i++) {
  lightWeightMap.remove("sparrow" + i);
}

entries

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

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

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

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

Error codes

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

ID	Error Message
10200011	The entries method cannot be bound.

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();
}

// You are not advised to use the set, setValueAt, remove, or removeAt APIs in entries because they may cause unpredictable risks such as infinite loops. You can use the for loop when inserting or deleting data.
let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
for(let i = 0; i < 10; i++) {
  lightWeightMap.set("sparrow" + i, 123);
}
for(let i = 0; i < 10; i++) {
  lightWeightMap.remove("sparrow" + i);
}

toString

toString(): String

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

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
String	String obtained.

Error codes

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

ID	Error Message
10200011	The toString method cannot be bound.

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.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

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

Error codes

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

ID	Error Message
10200011	The Symbol.iterator method cannot be bound.

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();
}

// You are not advised to use the set, setValueAt, remove, or removeAt APIs in Symbol.iterator because they may cause unpredictable risks such as infinite loops. You can use the for loop when inserting or deleting data.
let lightWeightMap: LightWeightMap<string, number> = new LightWeightMap();
for(let i = 0; i < 10; i++) {
  lightWeightMap.set("sparrow" + i, 123);
}
for(let i = 0; i < 10; i++) {
  lightWeightMap.remove("sparrow" + i);
}