@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 follows the principle of FIFO only and 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 '@ohos.util.Deque'; 

Deque

Attributes

System capability: SystemCapability.Utils.Lang

constructor

constructor()

A constructor used to create a Deque instance.

System capability: SystemCapability.Utils.Lang

Error codes

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

Example

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

insertFront

insertFront(element: T): void

Inserts an element at the front of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Error codes

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

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 : "Dylon", age : "13"};
deque.insertFront(c);
deque.insertFront(false);

insertEnd

insertEnd(element: T): void

Inserts an element at the end of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Error codes

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

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 : "Dylon", age : "13"};
deque.insertEnd(c);
deque.insertEnd(false);

has

has(element: T): boolean

Checks whether this container has the specified element.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

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.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

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.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

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.

System capability: SystemCapability.Utils.Lang

Parameters

callbackFn

Error codes

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

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.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

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.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

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.

NOTE

This API cannot be used in .ets files.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

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();
}