@ohos.util.Deque (Linear Container Deque)

Double-ended queue (deque) is a sequence container implemented based on the queue data structure that follows the principles of First In First Out (FIFO) and Last In First Out (LIFO). It allows insertion and removal of elements at both the ends. Deque can dynamically adjust the capacity based on project requirements. It doubles the capacity each time. Deque differs from Queue and Vector mainly in the following aspects:

Queue allows element removal at the front and insertion at the rear.

Vector supports insertion and deletion of elements in between, as well as at both the ends. When compared with Vector, Deque is more efficient in inserting and removing header elements, but less efficient in accessing elements.

Recommended use case: Use Deque when you need to frequently insert or remove elements at both the ends of a container.

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 { Deque } from '@kit.ArkTS';

Deque

Attributes

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

System capability: SystemCapability.Utils.Lang

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

constructor

constructor()

A constructor used to create a Deque 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 Deque's constructor cannot be directly invoked.

Example

let deque: Deque<string|number|boolean|Object> = new Deque();

insertFront

insertFront(element: T): void

Inserts an element at the front of this container.

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
element	T	Yes	Target element.

Error codes

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

ID	Error Message
10200011	The insertFront method cannot be bound.

Example

class C1 {
  name: string = ""
  age: string = ""
}
let deque: Deque<string|number|boolean|Array<number>|C1> = new Deque();
deque.insertFront("a");
deque.insertFront(1);
let b = [1, 2, 3];
deque.insertFront(b);
let c: C1 = {name : "Dylan", age : "13"};
deque.insertFront(c);
deque.insertFront(false);

insertEnd

insertEnd(element: T): void

Inserts an element at the end of this container.

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
element	T	Yes	Target element.

Error codes

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

ID	Error Message
10200011	The insertEnd method cannot be bound.

Example

class C1 {
  name: string = ""
  age: string = ""
}

let deque: Deque<string|number|boolean|Array<number>|C1> = new Deque();
deque.insertEnd("a");
deque.insertEnd(1);
let b = [1, 2, 3];
deque.insertEnd(b);
let c: C1 = {name : "Dylan", age : "13"};
deque.insertEnd(c);
deque.insertEnd(false);

has

has(element: T): boolean

Checks whether this container 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
element	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 deque: Deque<string> = new Deque();
deque.insertFront("squirrel");
let result = deque.has("squirrel");

popFirst

popFirst(): T

Removes the first element of this container.

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

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	First element removed.

Error codes

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

ID	Error Message
10200011	The popFirst method cannot be bound.

Example

let deque: Deque<number> = new Deque();
deque.insertFront(2);
deque.insertFront(4);
deque.insertEnd(5);
deque.insertFront(2);
deque.insertFront(4);
let result = deque.popFirst();

popLast

popLast(): T

Removes the last element of this container.

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

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	Last element removed.

Error codes

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

ID	Error Message
10200011	The popLast method cannot be bound.

Example

let deque: Deque<number> = new Deque();
deque.insertFront(2);
deque.insertEnd(4);
deque.insertFront(5);
deque.insertFront(2);
deque.insertFront(4);
let result = deque.popLast();

forEach

forEach(callbackFn: (value: T, index?: number, deque?: Deque<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

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.
deque	Deque<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 deque: Deque<number> = new Deque();
deque.insertFront(2);
deque.insertEnd(4);
deque.insertFront(5);
deque.insertEnd(4);
deque.forEach((value: number, index?: number|undefined, deque?: Deque<number>|undefined):void => {
  console.log("value:" + value, "index:" + index);
});

getFirst

getFirst(): T

Obtains the first element of this container.

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

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	First element of the T type 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 deque: Deque<number> = new Deque();
deque.insertEnd(2);
deque.insertEnd(4);
deque.insertFront(5);
deque.insertFront(4);
let result = deque.getFirst();

getLast

getLast(): T

Obtains the last element of this container.

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

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	Last element of the T type obtained.

Error codes

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

ID	Error Message
10200011	The getLast method cannot be bound.

Example

let deque: Deque<number> = new Deque();
deque.insertFront(2);
deque.insertFront(4);
deque.insertFront(5);
deque.insertFront(4);
let result = deque.getLast();

[Symbol.iterator]

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

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

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 deque: Deque<number> = new Deque();
deque.insertFront(2);
deque.insertFront(4);
deque.insertFront(5);
deque.insertFront(4);

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

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