@ohos.util.List (Linear Container List)

List is implemented based on the singly linked list. Each node has a reference pointing to the next element. When querying an element, the system traverses the list from the beginning. List offers efficient insertion and removal operations but supports low query efficiency. List allows null elements.

Unlike LinkedList, which is a doubly linked list, List is a singly linked list that does not support insertion or removal at both ends.

NOTE

Although using [index] in List can obtain an element with the given index, this operation will result in undefined results. Due to this reason, get() method is recommended.

Recommended use case: Use List for frequent insertion and removal operations when a singly linked list is required.

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 { List } from '@kit.ArkTS';

List

Attributes

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

System capability: SystemCapability.Utils.Lang

constructor

constructor()

A constructor used to create a List 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.

Example

let list: List<string|number|boolean|object> = new List();

add

add(element: T): boolean

Adds 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

Return value

Error codes

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

Example

let list: List<string|number|boolean|object> = new List();
let result1 = list.add("a");
let result2 = list.add(1);
let b = [1, 2, 3];
let result3 = list.add(b);
class C {
  name: string = ''
  age: string = ''
}
let c: C = {name : "Dylan", age : "13"};
let result4 = list.add(c);
let result5 = list.add(false);

insert

insert(element: T, index: number): void

Inserts an element at the specified position in this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Error codes

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

Example

let list: List<string|number|boolean> = new List();
list.insert("A", 0);
list.insert(0, 1);
list.insert(true, 2);

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

Return value

Error codes

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

Example

let list: List<string> = new List();
list.add("squirrel");
let result = list.has("squirrel");

get

get(index: number): T

Obtains the element at the specified position in this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(2);
list.add(1);
list.add(2);
list.add(4);
let result = list.get(2);

getLastIndexOf

getLastIndexOf(element: T): number

Obtains the index of the last occurrence of the specified element in this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(2);
list.add(1);
list.add(2);
list.add(4);
let result = list.getLastIndexOf(2);

getIndexOf

getIndexOf(element: T): number

Obtains the index of the first occurrence of the specified element in this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(2);
list.add(1);
list.add(2);
list.add(4);
let result = list.getIndexOf(2);

equal

equal(obj: Object): boolean

Compares whether a specified object is equal to this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
let obj: List<number> = new List();
obj.add(2);
obj.add(4);
obj.add(5);
let result = list.equal(obj);

removeByIndex

removeByIndex(index: number): T

Searches for an element based on its index and then removes it.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(2);
list.add(4);
let result = list.removeByIndex(2);

remove

remove(element: T): boolean

Removes the first occurrence of the specified element from this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.remove(2);

replaceAllElements

replaceAllElements(callbackFn: (value: T, index?: number, list?: List<T>) => T, thisArg?: Object): void

Replaces all elements in this container with new elements, and returns the new ones.

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

System capability: SystemCapability.Utils.Lang

Parameters

callbackFn

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.replaceAllElements((value: number) => {
  // Add the user operation logic based on the actual scenario.
  return value;
});

forEach

forEach(callbackFn: (value: T, index?: number, List?: List<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

callbackFn

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.forEach((value: number, index?: number) => {
  console.log("value:" + value, "index:" + index);
});

sort

sort(comparator: (firstValue: T, secondValue: T) => number): void

Sorts elements in this container.

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

System capability: SystemCapability.Utils.Lang

Parameters

comparator

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.sort((a: number, b: number) => a - b); // The elements are sorted in ascending order.
list.sort((a: number, b: number) => b - a); // The elements are sorted in descending order.

getSubList

getSubList(fromIndex: number, toIndex: number): List<T>

Obtains elements within a range in this container, including the element at the start position but not that at the end position, and returns these elements as a new List instance.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.getSubList(1, 3);

clear

clear(): void

Clears this container and sets its length to 0.

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.

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.clear();

set

set(index: number, element: T): T

Replaces an element at the specified position in this container with a given element.

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

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

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

Example

let list: List<number|string> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.set(2, "b");

convertToArray

convertToArray(): Array<T>

Converts this container into an array.

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.convertToArray();

isEmpty

isEmpty(): boolean

Checks whether this container is empty (contains no element).

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.isEmpty();

getFirst

getFirst(): T

Obtains the first element in this container.

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

Example

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

getLast

getLast(): T

Obtains the last element in this container.

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

System capability: SystemCapability.Utils.Lang

Return value

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.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

Error codes

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

Example

let list: List<number> = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);

// Method 1:
let items = Array.from(list)
for (let item of items) {
  console.log("value: " + item);
}

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

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