Linear Container List

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.

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.

Modules to Import

import List from '@ohos.util.List';  

List

Attributes

System capability: SystemCapability.Utils.Lang

constructor

constructor()

A constructor used to create a List instance.

System capability: SystemCapability.Utils.Lang

Example

let list = new List();

add

add(element: T): boolean

Adds an element at the end of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Example

let list = new List();
let result = list.add("a");
let result1 = list.add(1);
let b = [1, 2, 3];
list.add(b);
let c = {name : "lala", age : "13"};
let result3 = 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

Example

let list = 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

Return value

Example

let list = new List();
let result = list.has("Ahfbrgrbgnutfodgorrogorg");
list.add("Ahfbrgrbgnutfodgorrogorg");
let result1 = list.has("Ahfbrgrbgnutfodgorrogorg");

get

get(index: number): T

Obtains the element at the specified position in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Example

let list = 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

Return value

Example

let list = 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

Return value

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(2);
list.add(1);
list.add(2);
list.add(4);
list.getIndexOf(2);
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

Return value

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(2);
let obj1 = new List();
obj1.add(2);
obj1.add(4);
obj1.add(5);
list.equal(obj1);
let obj2 = {name : "lala", age : "13"};
let result = list.equal(obj2);

removeByIndex

removeByIndex(index: number): T

Removes an element at the specified position from this container.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Example

let list = 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

Return value

Example

let list = 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.

System capability: SystemCapability.Utils.Lang

Parameters

callbackfn

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.replaceAllElements((value: number, index: number) => {
  return value = 2 * value;
});
list.replaceAllElements((value: number, index: number) => {
  return value = value - 2;
});

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.

System capability: SystemCapability.Utils.Lang

Parameters

callbackfn

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.forEach((value, index) => {
    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

comparator

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.sort((a: number, b: number) => a - b);
list.sort((a: number, b: number) => b - a);

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.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
let result = list.getSubList(2, 4);
let result1 = list.getSubList(4, 3);
let result2 = list.getSubList(2, 6);

clear

clear(): void

Clears this container and sets its length to 0.

System capability: SystemCapability.Utils.Lang

Example

let list = 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

Return value

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);
list.set(2, "b");

convertToArray

convertToArray(): Array<T>

Converts this container into an array.

System capability: SystemCapability.Utils.Lang

Return value

Example

let list = 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

Example

let list = 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

Example

let list = 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

Example

let list = 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.

System capability: SystemCapability.Utils.Lang

Return value

Example

let list = new List();
list.add(2);
list.add(4);
list.add(5);
list.add(4);

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

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