@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

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

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.

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

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

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

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

Name	Type	Mandatory	Description
element	T	Yes	Target element.
index	number	Yes	Index of the position where the element is to be inserted. The value must be less than or equal to int32_max, that is, 2147483647.

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; 3. Parameter verification failed.
10200001	The value of index is out of range.
10200011	The insert method cannot be bound.

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

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 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

Name	Type	Mandatory	Description
index	number	Yes	Position index of the target element. The value must be less than or equal to int32_max, that is, 2147483647.

Return value

Type	Description
T	Element obtained.

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 get method cannot be bound.

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

Name	Type	Mandatory	Description
element	T	Yes	Target element.

Return value

Type	Description
number	Returns the index if obtained; returns -1 otherwise.

Error codes

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

ID	Error Message
10200011	The getLastIndexOf method cannot be bound.

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

Name	Type	Mandatory	Description
element	T	Yes	Target element.

Return value

Type	Description
number	Returns the position index if obtained; returns -1 otherwise.

Error codes

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

ID	Error Message
10200011	The getIndexOf method cannot be bound.

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

Name	Type	Mandatory	Description
obj	Object	Yes	Object used for comparison.

Return value

Type	Description
boolean	Returns true if the two are equal; returns false otherwise.

Error codes

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

ID	Error Message
10200011	The equal method cannot be bound.

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

Name	Type	Mandatory	Description
index	number	Yes	Position index of the target element. The value must be less than or equal to int32_max, that is, 2147483647.

Return value

Type	Description
T	Element removed.

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.
10200001	The value of index is out of range.
10200011	The removeByIndex method cannot be bound.

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

Name	Type	Mandatory	Description
element	T	Yes	Target element.

Return value

Type	Description
boolean	Returns true if the element is removed successfully; returns false otherwise.

Error codes

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

ID	Error Message
10200011	The remove method cannot be bound.

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

Name	Type	Mandatory	Description
callbackFn	function	Yes	Callback invoked for the replacement.
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.
list	List<T>	No	Instance that calls the replaceAllElements 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 replaceAllElements method cannot be bound.

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

Name	Type	Mandatory	Description
callbackFn	function	Yes	Callback invoked for the replacement.
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.
List	List<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 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

Name	Type	Mandatory	Description
comparator	function	Yes	Callback invoked for sorting.

comparator

Name	Type	Mandatory	Description
firstValue	T	Yes	Previous element.
secondValue	T	Yes	Next element.

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 sort method cannot be bound.

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

Name	Type	Mandatory	Description
fromIndex	number	Yes	Index of the start position.
toIndex	number	Yes	Index of the end position.

Return value

Type	Description
List<T>	New List instance obtained.

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.
10200001	The value of fromIndex or toIndex is out of range.
10200011	The getSubList method cannot be bound.

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.

ID	Error Message
10200011	The clear method cannot be bound.

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

Name	Type	Mandatory	Description
index	number	Yes	Position index of the target element. The value must be less than or equal to int32_max, that is, 2147483647.
element	T	Yes	Element to be used for replacement.

Return value

Type	Description
T	New element.

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.
10200001	The value of index is out of range.
10200011	The set method cannot be bound.

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

Type	Description
Array<T>	Array obtained.

Error codes

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

ID	Error Message
10200011	The convertToArray method cannot be bound.

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

Type	Description
boolean	Returns true if the container is empty; returns false otherwise.

Error codes

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

ID	Error Message
10200011	The isEmpty method cannot be bound.

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

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 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

Type	Description
T	The last element 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 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

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 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();
}