harmony 鸿蒙@ohos.util.List (Linear Container List)

  • 2022-08-09
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@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.

Recommended use case: Use List for frequent insertion and removal operations.

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 '@ohos.util.List';

List

Attributes

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.

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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
element T Yes Target element.

Return value

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 : "Dylon", 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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
element T Yes Target element.
index number Yes Index of the position where the element is to be inserted.

Error codes

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

ID Error Message
10200011 The insert method cannot be bound.
10200001 The value of index is out of range.

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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
element T Yes Target element.

Return value

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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
index number Yes Position index of the target element.

Return value

Value Type Description
T Element obtained.

Error codes

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

ID Error Message
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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
element T Yes Target element.

Return value

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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
element T Yes Target element.

Return value

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.

System capability: SystemCapability.Utils.Lang

Parameters

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

Return value

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

Removes an element at the specified position from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
index number Yes Position index of the target element.

Return value

Value Type Description
T Element removed.

Error codes

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

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

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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
element T Yes Target element.

Return value

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&lt;T&gt;) => T, thisArg?: Object): void

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

System capability: SystemCapability.Utils.Lang

Parameters

Name Value 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 Value 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&lt;T&gt; No Instance that calls the replaceAllElements API. The default value is this instance.

Error codes

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

ID Error Message
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&lt;T&gt;) => 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

Name Value 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 Value 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&lt;T&gt; No Instance that calls the forEach API. The default value is this instance.

Error codes

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

ID Error Message
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.

System capability: SystemCapability.Utils.Lang

Parameters

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

comparator

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

Error codes

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

ID Error Message
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&lt;T&gt;

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.

System capability: SystemCapability.Utils.Lang

Parameters

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

Return value

Value Type Description
List&lt;T&gt; New List instance obtained.

Error codes

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

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

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.

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.

System capability: SystemCapability.Utils.Lang

Parameters

Name Value Type Mandatory Description
index number Yes Position index of the target element.
element T Yes Element to be used for replacement.

Return value

Value Type Description
T New element.

Error codes

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

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

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&lt;T&gt;

Converts this container into an array.

System capability: SystemCapability.Utils.Lang

Return value

Value Type Description
Array&lt;T&gt; 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).

System capability: SystemCapability.Utils.Lang

Return value

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.

System capability: SystemCapability.Utils.Lang

Return value

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.

System capability: SystemCapability.Utils.Lang

Return value

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&lt;T&gt;

Obtains an iterator, each item of which is a JavaScript object.

System capability: SystemCapability.Utils.Lang

Return value

Value Type Description
IterableIterator&lt;T&gt; 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();
}

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