目录

@ohos.util.Deque (Linear Container Deque)

Double-Ended Queue (Deque) is a data structure implemented based on a circular queue. It supports insertion and deletion of elements at both ends. It follows the principles of First In First Out (FIFO) and Last In First Out (LIFO). Deque can dynamically adjust the capacity based on project requirements. It doubles the capacity each time.

Queue allows element removal at the front and insertion at the rear. Compared with Queue, which only allows element deletion at the front and insertion at the back, Deque permits insertion and deletion at both ends.

Both ArrayList and Deque support insertion and deletion at the ends, but Deque does not support insertion in the middle. Deque is more efficient than an ArrayList for inserting and deleting elements at the front, whereas an ArrayList excels in element access efficiency.

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:

  • 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 { Deque } from '@kit.ArkTS';

Deque

[h2]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 Deque.

[h2]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 = new Deque<string | number | boolean | Object>();

[h2]insertFront

insertFront(element: T): void

Inserts an element at the front of this Deque.

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 = new Deque<string | number | boolean | Array<number> | C1>();
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);
console.info("result:", deque[0]);  // result: false

[h2]insertEnd

insertEnd(element: T): void

Inserts an element at the end of this Deque.

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 = new Deque<string | number | boolean | Array<number> | C1>();
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);
console.info("result:", deque[0]);  // result: a

[h2]has

has(element: T): boolean

Checks whether this Deque 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 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 Utils Error Codes.

ID Error Message
10200011 The has method cannot be bound.

Example

let deque = new Deque<string>();
deque.insertFront("squirrel");
let result = deque.has("squirrel");
console.info("result:", result);  // result: true

[h2]popFirst

popFirst(): T

Removes the first element of this Deque.

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

[h2]popLast

popLast(): T

Removes the last element of this Deque.

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 = new Deque<number>();
deque.insertFront(2);
deque.insertEnd(6);
deque.insertFront(5);
deque.insertFront(2);
deque.insertFront(4);
let result = deque.popLast();
console.info("result:", result);  // result: 6

[h2]forEach

forEach(callbackFn: (value: T, index?: number, deque?: Deque<T>) => void, thisArg?: Object): void

Uses a callback to traverse each element in the Deque instance.

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 Deque.
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 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 = new Deque<number>();
deque.insertFront(2);
deque.insertEnd(3);
deque.insertFront(1);
deque.insertEnd(4);
deque.forEach((value: number, index: number): void => {
  console.info("value:" + value, "index:" + index);
});
/*
Output: value:1 index:0
        value:2 index:1
        value:3 index:2
        value:4 index:3
*/

[h2]getFirst

getFirst(): T

Obtains the first element of this Deque.

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 = new Deque<number>();
deque.insertEnd(2);
deque.insertEnd(4);
deque.insertFront(5);
deque.insertFront(4);
let result = deque.getFirst();
console.info("result:", result);  // result: 4

[h2]getLast

getLast(): T

Obtains the last element of this Deque.

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 = new Deque<number>();
deque.insertFront(2);
deque.insertFront(4);
deque.insertFront(5);
deque.insertFront(4);
let result = deque.getLast();
console.info("result:", result);  // result: 2

[h2][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 deque = new Deque<number>();
deque.insertFront(2);
deque.insertFront(4);
deque.insertFront(5);
deque.insertFront(4);

// Method 1:
for (let item of deque) {
  console.info("value:" + item);
}
/*
Output: 4
        5
        4
        2
*/

// Method 2:
let iter = deque[Symbol.iterator]();
let temp:IteratorResult<number> = iter.next();
while(!temp.done) {
  console.info("value:" + temp.value);
  temp = iter.next();
}
/*
Output: 4
        5
        4
        2
*/