目录

@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:

  • 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.

  • Container classes, implemented in static languages, have restrictions on storage locations and properties, and do not support custom properties or methods.

Specifications

If the key stored in LightWeightMap is of the number type and the value is greater than INT32_MAX or less than INT32_MIN, the operation result of LightWeightMap may be different from the expected result.

This is because the storage structure changes in such cases.

For example, 1758783600000 is greater than INT32_MAX and is stored as TaggedDouble; 1758783600 is less than INT32_MIN and is stored as TaggedInt. Due to these differences in storage modes, the hash algorithm will generate different hash values, leading to inconsistent mapping results and ultimately causing discrepancies from expected outcomes.

let mp = new LightWeightMap<number, number>();
let key = 1758783600000 / 1000;  // 1758783600000 > INT32_MAX
mp.set(key, 1001);
console.info("result:", mp.hasKey(1758783600));  // result: false
console.info("result:", mp.hasKey(key));  // result: true

Modules to Import

import { LightWeightMap } from '@kit.ArkTS';

LightWeightMap

[h2]Properties

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

System capability: SystemCapability.Utils.Lang

Name Type Read-Only Optional Description
length number Yes No Number of elements in a LightWeightMap.

[h2]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 = new LightWeightMap<string, number>();

[h2]isEmpty

isEmpty(): boolean

Checks whether this LightWeightMap 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 Check result. The value true is returned if the LightWeightMap is empty; otherwise, false is returned.

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 = new LightWeightMap<string, number>();
let result = lightWeightMap.isEmpty();
console.info("result:", result);  // result: true

[h2]hasAll

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

Checks whether this LightWeightMap 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 Check result. The value true is returned if all the elements in the specified LightWeightMap are contained; otherwise, false is returned.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let map = new LightWeightMap<string, number>();
map.set("sparrow", 356);
let result = lightWeightMap.hasAll(map);
console.info("result = ", result); // result = true

[h2]hasKey

hasKey(key: K): boolean

Checks whether this LightWeightMap has 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 Check result. The value true is returned if the specified key is contained; otherwise, false is returned.

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

[h2]hasValue

hasValue(value: V): boolean

Checks whether this LightWeightMap has 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 Operation result. The value true is returned if the specified value is contained; otherwise, false is returned.

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

[h2]increaseCapacityTo

increaseCapacityTo(minimumCapacity: number): void

Increases the capacity of this LightWeightMap. If the passed-in capacity is greater than or equal to the number of elements in this LightWeightMap, the capacity is changed to the new capacity. If the passed-in capacity is less than the number of elements in this LightWeightMap, 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 LightWeightMap.

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 = new LightWeightMap<string, number>();
lightWeightMap.increaseCapacityTo(10);

[h2]get

get(key: K): V

Obtains the value of the specified key in this LightWeightMap.

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

[h2]getIndexOfKey

getIndexOfKey(key: K): number

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

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 Index of the element. If no match is found, -1 is returned.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.getIndexOfKey("sparrow");
console.info("result:", result);  // result: 0

[h2]getIndexOfValue

getIndexOfValue(value: V): number

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

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 Index of the element. If no match is found, -1 is returned.

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

[h2]getKeyAt

getKeyAt(index: number): K

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

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 Key obtained. If the key is not found, undefined is returned.

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

[h2]setAll

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

Adds all elements in a LightWeightMap to this LightWeightMap.

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 whose elements are to be added to the current LightWeightMap.

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

[h2]set

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

Adds or updates an element in this LightWeightMap.

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

[h2]remove

remove(key: K): V

Removes an element with the specified key from this LightWeightMap.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.remove("sparrow");
console.info("result:", result);  // result: 356

[h2]removeAt

removeAt(index: number): boolean

Removes an element at the specified position from this LightWeightMap.

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 Operation result. The value true is returned if the element is removed; otherwise, false is returned.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.removeAt(1);
console.info("result:", result);  // result: true

[h2]setValueAt

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

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

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 Operation result. The value true is returned if the value is set successfully; otherwise, false is returned.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
lightWeightMap.setValueAt(1, 3546);
console.info("result:", lightWeightMap.get("squirrel"));  // result: 3546

[h2]getValueAt

getValueAt(index: number): V

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

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

[h2]clear

clear(): void

Clears this LightWeightMap 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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
lightWeightMap.clear();
let result = lightWeightMap.isEmpty();
console.info("result:", result);  // result: true

[h2]keys

keys(): IterableIterator<K>

Returns an iterator that contains all the keys in this LightWeightMap.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let keys = lightWeightMap.keys();
for (let key of keys) {
  console.info("key:", key);
}
// key: sparrow
// key: squirrel

[h2]values

values(): IterableIterator<V>

Returns an iterator that contains all the values in this LightWeightMap.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let values = lightWeightMap.values();
for (let value of values) {
  console.info("value:", value);
}
// value: 356
// value: 123

[h2]forEach

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

Uses a callback to traverse the elements in this LightWeightMap and obtain their 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 LightWeightMap.
thisArg Object No Value of this to use when callbackFn is invoked. The default value is this instance.

callbackFn parameters

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 = new LightWeightMap<string, number>();
lightWeightMap.set("sparrow", 123);
lightWeightMap.set("gull", 357);
lightWeightMap.forEach((value: number, key: string) => {
  console.info("value:" + value, "key:" + key);
});
// value:123 key:sparrow
// value:357 key:gull
// 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 = new LightWeightMap<string, number>();
for(let i = 0; i < 10; i++) {
  lightWeightMap.set("sparrow" + i, 123);
}
for(let i = 0; i < 10; i++) {
  lightWeightMap.remove("sparrow" + i);
}

[h2]entries

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

Returns an iterator that contains all the elements in this LightWeightMap.

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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let iter = lightWeightMap.entries();
let temp: IteratorResult<Object[]> = iter.next();
while(!temp.done) {
  console.info("key:" + temp.value[0]);
  console.info("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 = new LightWeightMap<string, number>();
for(let i = 0; i < 10; i++) {
  lightWeightMap.set("sparrow" + i, 123);
}
for(let i = 0; i < 10; i++) {
  lightWeightMap.remove("sparrow" + i);
}

[h2]toString

toString(): String

Concatenates the elements in this LightWeightMap 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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let result = lightWeightMap.toString();
console.info("result:", result);  // result: sparrow:356,squirrel:123

[h2][Symbol.iterator]

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

Returns an iterator. Each item of the iterator 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 = new LightWeightMap<string, number>();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);

// Method 1:
for (let item of lightWeightMap) {
  console.info("key:", item[0]);
  console.info("value:", item[1]);
}
// key: sparrow
// value: 356
// key: squirrel
// value: 123

// Method 2:
let iter = lightWeightMap[Symbol.iterator]();
let temp: IteratorResult<Object[]> = iter.next();
while(!temp.done) {
  console.info("key:", temp.value[0]);
  console.info("value:", temp.value[1]);
  temp = iter.next();
}
// key: sparrow
// value: 356
// key: squirrel
// value: 123
// 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 = new LightWeightMap<string, number>();
for(let i = 0; i < 10; i++) {
  lightWeightMap.set("sparrow" + i, 123);
}
for(let i = 0; i < 10; i++) {
  lightWeightMap.remove("sparrow" + i);
}