@ohos.util.Queue (Linear Container Queue)

Queue follows the principle of First In First Out (FIFO). It supports insertion of elements at the end and removal from the front of the queue. Queue is implemented based on the queue data structure.

Unlike Deque, which supports insertion and removal at both the ends, Queue supports insertion at one end and removal at the other end.

Recommended use case: Use Queue in FIFO scenarios.

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 Queue from '@ohos.util.Queue';

Queue

Attributes

System capability: SystemCapability.Utils.Lang

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

constructor

constructor()

A constructor used to create a Queue instance.

System capability: SystemCapability.Utils.Lang

Error codes

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

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

Example

let queue : Queue<number|string|Object> = new Queue();

add

add(element: T): boolean

Adds an element at the end of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
element	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

class C1 {
  name: string = ""
  age: string = ""
}
let queue : Queue<number|string|C1|number[]> = new Queue();
let result = queue.add("a");
let result1 = queue.add(1);
let b = [1, 2, 3];
let result2 = queue.add(b);
let c : C1 = {name : "Dylon", age : "13"};
let result3 = queue.add(c);

pop

pop(): T

Removes the first element from this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	Element removed.

Error codes

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

ID	Error Message
10200011	The pop method cannot be bound.

Example

let queue : Queue<number> = new Queue();
queue.add(2);
queue.add(4);
queue.add(5);
queue.add(2);
queue.add(4);
let result = queue.pop();

getFirst

getFirst(): T

Obtains the first element of this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	The first element obtained.

Error codes

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

ID	Error Message
10200011	The getFirst method cannot be bound.

Example

let queue : Queue<number> = new Queue();
queue.add(2);
queue.add(4);
queue.add(5);
queue.add(2);
let result = queue.getFirst();

forEach

forEach(callbackFn: (value: T, index?: number, Queue?: Queue<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	Yes	Value of the element that is currently traversed.
index	number	No	Position index of the element that is currently traversed. The default value is 0.
Queue	Queue<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 queue : Queue<number> = new Queue();
queue.add(2);
queue.add(4);
queue.add(5);
queue.add(4);
queue.forEach((value : number, index ?: number) : void => {
  console.log("value:" + value, "index:" + index);
});

[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 queue : Queue<number> = new Queue();
queue.add(2);
queue.add(4);
queue.add(5);
queue.add(4);

// Method 1:
while(queue.length) {
  let item = queue.pop()
  console.log("value:" + item);
}

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