@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

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

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();

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.

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();
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.

Error codes

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

ID Error Message
10200011 The hasAll method cannot be bound.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 356);
let map = 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

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 = 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

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 = 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

Error codes

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

ID Error Message
10200011 The increaseCapacityTo method cannot be bound.

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.

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();
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

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 = 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

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 = 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

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.

Error codes

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

ID Error Message
10200011 The getKeyAt method cannot be bound.
10200001 The value of index is out of range.

Example

let lightWeightMap = 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

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 Utils Error Codes.

ID Error Message
10200011 The setAll method cannot be bound.

Example

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

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();
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

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();
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

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.

Error codes

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

ID Error Message
10200011 The removeAt method cannot be bound.

Example

let lightWeightMap = 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

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.

Error codes

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

ID Error Message
10200011 The setValueAt method cannot be bound.
10200001 The value of index is out of range.

Example

let lightWeightMap = 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

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

Return value

Type Description
V Value obtained.

Error codes

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

ID Error Message
10200011 The getValueAt method cannot be bound.
10200001 The value of index is out of range.

Example

let lightWeightMap = 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.

ID Error Message
10200011 The clear method cannot be bound.

Example

let lightWeightMap = 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

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();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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.

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();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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.

Error codes

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

ID Error Message
10200011 The forEach method cannot be bound.

Example

let lightWeightMap = new LightWeightMap();
lightWeightMap.set("sparrow", 123);
lightWeightMap.set("gull", 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.

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();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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.

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();
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.

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();
lightWeightMap.set("squirrel", 123);
lightWeightMap.set("sparrow", 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;
}