@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 sorts data by hash value. 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.

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

Modules to Import

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

HashSet

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 HashSet.

Example

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

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.

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

Example

let hashSet = new HashSet<number>();

isEmpty

isEmpty(): boolean

Checks whether this HashSet 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 HashSet 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 hashSet = new HashSet<number>();
let result = hashSet.isEmpty();
console.info("result:", result);  // result: true

has

has(value: T): boolean

Checks whether this HashSet has the specified element.

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	T	Yes	Target element.

Return value

Type	Description
boolean	Operation result. The value true is returned if the specified element is 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; 3. Parameter verification failed.
10200011	The has method cannot be bound.

Example

let hashSet = new HashSet<string>();
hashSet.add("squirrel");
let result = hashSet.has("squirrel");
console.info("result:", result);  // result: true

add

add(value: T): boolean

Adds elements to this HashSet.

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	T	Yes	Target element.

Return value

Type	Description
boolean	Operation result. The value true is returned if the element is added; 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.
10200011	The add method cannot be bound.

Example

let hashSet = new HashSet<string>();
let result = hashSet.add("squirrel");
console.info("result:", result);  // result: true

remove

remove(value: T): boolean

Removes an element from this HashSet.

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	T	Yes	Target element.

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; 3. Parameter verification failed.
10200011	The remove method cannot be bound.

Example

let hashSet = new HashSet<string>();
hashSet.add("squirrel");
hashSet.add("sparrow");
let result = hashSet.remove("sparrow");
console.info("result:", result);  // result: true

clear

clear(): void

Clears this HashSet 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 hashSet = new HashSet<string>();
hashSet.add("squirrel");
hashSet.add("sparrow");
hashSet.clear();
let result = hashSet.isEmpty();
console.info("result:", result);  // result: true

values

values(): IterableIterator<T>

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

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<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 hashSet = new HashSet<string>();
hashSet.add("squirrel");
hashSet.add("sparrow");
let values = hashSet.values();
for (let value of values) {
  console.info("value:", value);
}
// value: squirrel
// value: sparrow

forEach

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

Uses a callback to traverse each element.

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 HashSet.
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	T	No	Value of the element that is currently traversed.
key	T	No	Key of the element that is currently traversed (same as value).
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.

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

// You are not advised to use the add and 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 = new HashSet<string>();
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]>

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

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<[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 hashSet = new HashSet<string>();
hashSet.add("squirrel");
hashSet.add("sparrow");
let iter = hashSet.entries();
let temp: IteratorResult<[string, string]> = iter.next();
while(!temp.done) {
  console.info("key:" + temp.value[0]);
  console.info("value:" + temp.value[1]);
  temp = iter.next();
}
// key:squirrel
// value:squirrel
// key:sparrow
// value:sparrow

// 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 = new HashSet<string>();
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<T>

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

// Method 1:
for (let item of hashSet) {
  console.info("value: " + item);
}
// value: squirrel
// value: sparrow

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

// 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 = new HashSet<string>();
for(let i = 0;i < 10;i++) {
  hashSet.add("sparrow" + i);
}
for(let i = 0;i < 10;i++) {
  hashSet.remove("sparrow" + i);
}