@ohos.util.HashSet (Nonlinear Container HashSet)

HashSet is implemented based on HashMap. In HashSet, only the value object is processed.

Unlike TreeSet, which stores and accesses data in sorted order, HashSet stores data in a random order. This means that HashSet may use a different order when storing and accessing elements. Both of them allow only unique elements. However, null values are allowed in HashSet, but not in TreeSet, because null values may affect the order of elements in the container.

Recommended use case: Use HashSet 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 { HashSet } from '@kit.ArkTS';

HashSet

Attributes

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

System capability: SystemCapability.Utils.Lang

Example

let hashSet: HashSet<number> = new HashSet();
hashSet.add(1);
hashSet.add(2);
hashSet.add(3);
hashSet.add(4);
hashSet.add(5);
let res = hashSet.length;

constructor

constructor()

A constructor used to create a HashSet 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.

Example

let hashSet: HashSet<number> = new HashSet();

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

Error codes

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

Example

const hashSet: HashSet<number> = new HashSet();
let result = hashSet.isEmpty();

has

has(value: T): boolean

Checks whether this container contains the specified element.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
let result = hashSet.has("squirrel");

add

add(value: T): boolean

Adds an element to this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let hashSet: HashSet<string> = new HashSet();
let result = hashSet.add("squirrel");

remove

remove(value: T): boolean

Removes an element from this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
hashSet.add("sparrow");
let result = hashSet.remove("sparrow");

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.

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
hashSet.add("sparrow");
hashSet.clear();

values

values(): IterableIterator<T>

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

Error codes

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

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
hashSet.add("sparrow");
let iter = hashSet.values();
let temp = iter.next();
while(!temp.done) {
  console.log("value:" + temp.value);
  temp = iter.next();
}

forEach

forEach(callbackFn: (value?: T, key?: T, set?: HashSet<T>) => 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

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|HashSet<T>|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.

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("sparrow");
hashSet.add("squirrel");
hashSet.forEach((value?: string, key?: string): void => {
  console.log("value:" + value, "key:" + key);
});

// You are not advised to use the set or remove 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 hashSet : HashSet<string> = new HashSet();
for(let i = 0;i < 10; i++) {
  hashSet.add("sparrow" + i);
}
for(let i = 0;i < 10; i++) {
  hashSet.remove("sparrow" + i);
}

entries

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

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

Error codes

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

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
hashSet.add("sparrow");
let iter = hashSet.entries();
let temp: IteratorResult<[string, string]> = 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 or remove 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 hashSet : HashSet<string> = new HashSet();
for(let i = 0;i < 10; i++) {
  hashSet.add("sparrow" + i);
}
for(let i = 0;i < 10; i++) {
  hashSet.remove("sparrow" + i);
}

[Symbol.iterator]

[Symbol.iterator](): IterableIterator&lt;T&gt;

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

Error codes

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

Example

let hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
hashSet.add("sparrow");

// Method 1:
let val: Array<string> = Array.from(hashSet.values())
for (let item of val) {
  console.log("value: " + item);
}

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

// You are not advised to use the set or remove 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 hashSet : HashSet<string> = new HashSet();
for(let i = 0;i < 10;i++) {
  hashSet.add("sparrow" + i);
}
for(let i = 0;i < 10;i++) {
  hashSet.remove("sparrow" + i);
}

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