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
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
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
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. |
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
Name | Value Type | Mandatory | Description |
---|---|---|---|
element | T | Yes | Target element. |
index | number | Yes | Index of the position where the element is to be inserted. |
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
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. |
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
Name | Value Type | Mandatory | Description |
---|---|---|---|
index | number | Yes | Position index of the target element. |
Return value
Value Type | Description |
---|---|
T | Element obtained. |
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
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. |
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
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. |
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
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. |
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
Name | Value Type | Mandatory | Description |
---|---|---|---|
index | number | Yes | Position index of the target element. |
Return value
Value Type | Description |
---|---|
T | Element removed. |
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
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. |
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
Name | Value Type | Mandatory | Description |
---|---|---|---|
callbackfn | function | Yes | Callback invoked for the replacement. |
thisArg | Object | No | Value to use when the callback is invoked. |
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. |
list | List<T> | No | Instance that invokes the replaceAllElements method. |
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
Name | Value Type | Mandatory | Description |
---|---|---|---|
callbackfn | function | Yes | Callback invoked to traverse the elements in the container. |
thisArg | Object | No | Value to use when the callback is invoked. |
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. |
List | List<T> | No | Instance that invokes the forEach method. |
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);
});
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. |
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
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<T> | New List instance obtained. |
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
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. |
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
Value Type | Description |
---|---|
Array<T> | Array obtained. |
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
Value Type | Description |
---|---|
boolean | Returns true if the container is empty; returns false otherwise. |
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
Value Type | Description |
---|---|
T | The first element obtained. |
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
Value Type | Description |
---|---|
T | The last element obtained. |
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
Value Type | Description |
---|---|
IterableIterator<T> | Iterator obtained. |
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;
}