@ohos.util.LightWeightSet (Nonlinear Container LightWeightSet)

LightWeightSet stores a set of values, each of which must be unique.

LightWeightSet 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 values in such a set are searched using hash values, which are stored in an array.

Compared with HashSet, which can also store values, LightWeightSet occupies less memory.

Recommended use case: Use LightWeightSet when you need a set that has only unique elements or need to deduplicate a set.

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

  • T: Type

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 LightWeightSet from '@ohos.util.LightWeightSet';  

LightWeightSet

Attributes

System capability: SystemCapability.Utils.Lang

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

constructor

constructor()

A constructor used to create a LightWeightSet instance.

System capability: SystemCapability.Utils.Lang

Error codes

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

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

Example

let lightWeightSet: LightWeightSet<number | string> = new LightWeightSet();

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 lightWeightSet: LightWeightSet<number> = new LightWeightSet();
let result = lightWeightSet.isEmpty();

add

add(obj: T): boolean

Adds an element to this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
obj T Yes Target element.

Return value

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

Error codes

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

ID Error Message
10200011 The add method cannot be bound.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
let result = lightWeightSet.add("squirrel");

addAll

addAll(set: LightWeightSet<T>): boolean

Adds all elements in a LightWeightSet instance to this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
set LightWeightSet<T> Yes LightWeightSet instance whose elements are to be added to the current container.

Return value

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

Error codes

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

ID Error Message
10200011 The addAll method cannot be bound.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let set: LightWeightSet<string> = new LightWeightSet();
set.add("gull");
let result = lightWeightSet.addAll(set);

hasAll

hasAll(set: LightWeightSet<T>): boolean

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

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
set LightWeightSet<T> Yes LightWeightSet instance to be used for comparison.

Return value

Type Description
boolean Returns true if all the elements in the specified LightWeightSet 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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let set: LightWeightSet<string> = new LightWeightSet();
set.add("sparrow");
let result = lightWeightSet.hasAll(set);

has

has(key: T): boolean

Checks whether this container has the specified key.

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
key T 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 has method cannot be bound.

Example

let lightWeightSet: LightWeightSet<number> = new LightWeightSet();
lightWeightSet.add(123);
let result = lightWeightSet.has(123);

equal

equal(obj: Object): boolean

Checks whether this container contains objects of the same type as the specified obj.

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
obj Object Yes LightWeightSet instance to be used for comparison.

Return value

Type Description
boolean Returns true if the container contains objects of the same type as the specified obj; returns false otherwise.

Error codes

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

ID Error Message
10200011 The equal method cannot be bound.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let obj = ["sparrow", "squirrel"];
let result = lightWeightSet.equal(obj);

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 the container.

Error codes

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

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

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.increaseCapacityTo(10);

getIndexOf

getIndexOf(key: T): number

Obtains the position index of the element with the specified key in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
key T Yes Key of the target element.

Return value

Type Description
number Position index of the element. If the element does not exist, a negative value is returned. The negative value consists of a minus sign and the position where the element (if available) should be. The position starts from 1.

Error codes

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

ID Error Message
10200011 The getIndexOf method cannot be bound.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let result = lightWeightSet.getIndexOf("sparrow");

remove

remove(key: T): T

Removes an element of the specified key from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name Type Mandatory Description
key T Yes Key of the target element.

Return value

Type Description
T 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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let result = lightWeightSet.remove("sparrow");

removeAt

removeAt(index: number): boolean

Removes the 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; 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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let result = lightWeightSet.removeAt(1);

getValueAt

getValueAt(index: number): T

Obtains the value of the 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
T Value obtained.

Error codes

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

ID Error Message
10200011 The getValueAt method cannot be bound.

Parameters

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let result = lightWeightSet.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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
lightWeightSet.clear();

toString

toString(): String

Obtains a string that contains all elements in this container.

System capability: SystemCapability.Utils.Lang

Return value

Type Description
String String obtained.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let result = lightWeightSet.toString();

toArray

toArray(): Array<T>

Obtains an array that contains all objects in this container.

System capability: SystemCapability.Utils.Lang

Return value

Type Description
Array<T> Array obtained.

Error codes

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

ID Error Message
10200011 The toArray method cannot be bound.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let result = lightWeightSet.toArray();

values

values(): IterableIterator<T>

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

System capability: SystemCapability.Utils.Lang

Return value

Type Description
IterableIterator<T> 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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let iter = lightWeightSet.values();
let index = 0;
while(index < lightWeightSet.length) {
  console.log(JSON.stringify(iter.next().value));
  index++;
}

forEach

forEach(callbackFn: (value?: T, key?: T, set?: LightWeightSet<T>) => 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 of this to use when callbackFn is invoked. The default value is this instance.

callbackFn

Name Type Mandatory Description
value T No Value of the element that is currently traversed. The default value is the value of the first key-value pair.
key T No Key of the element that is currently traversed (same as value). The default value is the key of the first key-value pair.
set LightWeightSet<T> No Instance that calls the forEach API. The default value is this instance.

Error codes

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

ID Error Message
10200011 The forEach method cannot be bound.

Example

let lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("sparrow");
lightWeightSet.add("gull");
lightWeightSet.forEach((value ?: string, key ?: string) => {
  console.log("value:" + value, "key:" + key);
});

entries

entries(): IterableIterator<[T, T]>

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

System capability: SystemCapability.Utils.Lang

Return value

Type Description
IterableIterator<[T, T]> 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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");
let iter = lightWeightSet.entries();
let index = 0;
while(index < lightWeightSet.length) {
  console.log(JSON.stringify(iter.next().value));
  index++;
}

[Symbol.iterator]

[Symbol.iterator](): IterableIterator<T>

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

Type Description
IterableIterator<T> 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 lightWeightSet: LightWeightSet<string> = new LightWeightSet();
lightWeightSet.add("squirrel");
lightWeightSet.add("sparrow");

// Method 1:
let nums: Array<string> = lightWeightSet.toArray()
for (let item of nums) {
  console.log("value:" + item);
}

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