harmony 鸿蒙@ohos.util.List (Linear Container List)
@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<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 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<T> | 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<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 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<T> | 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<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. |
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<T>
Converts this container into an array.
System capability: SystemCapability.Utils.Lang
Return value
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).
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<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. |
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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