harmony 鸿蒙@ohos.util.HashSet (Nonlinear Container HashSet)
@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 allows only unique elements. However, null values are allowed in HashSet, but not allowed in TreeSet.
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 '@ohos.util.HashSet';
HashSet
Attributes
System capability: SystemCapability.Utils.Lang
Name | Type | Readable | Writable | Description |
---|---|---|---|---|
length | number | Yes | No | Number of elements in a hash set (called container later). |
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.
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: HashSet<number> = new HashSet();
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 hashSet: HashSet<number> = new HashSet();
let result = hashSet.isEmpty();
has
has(value: T): boolean
Checks whether this container contains the specified element.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
value | T | Yes | Target element. |
Return value
Type | Description |
---|---|
boolean | Returns true if the specified element 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 hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
let result = hashSet.has("squirrel");
add
add(value: T): boolean
Adds an element to this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
value | 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 hashSet: HashSet<string> = new HashSet();
let result = hashSet.add("squirrel");
remove
remove(value: T): boolean
Removes an element from this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
value | T | Yes | Target 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 remove method cannot be bound. |
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.
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: 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.
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: 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.
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|HashSet<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 hashSet: HashSet<string> = new HashSet();
hashSet.add("sparrow");
hashSet.add("squirrel");
hashSet.forEach((value?: string, key?: string): void => {
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 hashSet: HashSet<string> = new HashSet();
hashSet.add("squirrel");
hashSet.add("sparrow");
let iter = hashSet.entries();
let temp: IteratorResult<string> = iter.next();
while(!temp.done) {
console.log("key:" + temp.value[0]);
console.log("value:" + temp.value[1]);
temp = iter.next();
}
[Symbol.iterator]
[Symbol.iterator](): IterableIterator<T>
Obtains an iterator, each item of which is a JavaScript object.
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: 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();
}
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