Nonlinear Container LightWeightMap
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.
LightWeightMap stores key-value (KV) pairs. Each key must be unique and have only one value.
LightWeightMap is based on generics and uses a lightweight structure. Keys in the map are searched using hash values, which are stored in an array.
Compared with HashMap, which can also store KV pairs, LightWeightMap occupies less memory.
Recommended use case: Use LightWeightMap when you need to store and access KV pairs.
Modules to Import
import LightWeightMap from '@ohos.util.LightWeightMap';
LightWeightMap
Attributes
System capability: SystemCapability.Utils.Lang
Name | Type | Readable | Writable | Description |
---|---|---|---|---|
length | number | Yes | No | Number of elements in a lightweight map (called container later). |
constructor
constructor()
A constructor used to create a LightWeightMap instance.
System capability: SystemCapability.Utils.Lang
Example
let lightWeightMap = new LightWeightMap();
isEmpty
isEmpty(): boolean
Checks whether this container is empty (contains no element).
System capability: SystemCapability.Utils.Lang
Return value
Type | Description |
---|---|
boolean | Returns true if the container is empty; returns false otherwise. |
Example
const lightWeightMap = new LightWeightMap();
let result = lightWeightMap.isEmpty();
hasAll
hasAll(map: LightWeightMap<K, V>): boolean
Checks whether this container contains all elements of the specified LightWeightMap instance.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
map | LightWeightMap<K, V> | Yes | LightWeightMap instance to be used for comparison. |
Return value
Type | Description |
---|---|
boolean | Returns true if all the elements in the specified LightWeightMap instance are contained; returns false otherwise. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let map = new LightWeightMap();
map.set("sdfs", 356);
let result = lightWeightMap.hasAll(map);
hasKey
hasKey(key: K): boolean;
Checks whether this container contains the specified key.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
key | K | Yes | Target key. |
Return value
Type | Description |
---|---|
boolean | Returns true if the specified key is contained; returns false otherwise. |
Example
let lightWeightMap = new LightWeightMap();
let result = lightWeightMap.hasKey;
lightWeightMap.hasKey("Ahfbrgrbgnutfodgorrogorgrogofdfdf");
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
let result1 = lightWeightMap.hasKey("Ahfbrgrbgnutfodgorrogorgrogofdfdf");
hasValue
hasValue(value: V): boolean
Checks whether this container contains the specified value.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
value | V | Yes | Target value. |
Return value
Type | Description |
---|---|
boolean | Returns true if the specified value is contained; returns false otherwise. |
Example
let lightWeightMap = new LightWeightMap();
let result = lightWeightMap.hasValue(123);
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
let result1 = lightWeightMap.hasValue(123);
increaseCapacityTo
increaseCapacityTo(minimumCapacity: number): void
Increases the capacity of this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
minimumCapacity | number | Yes | Minimum number of elements to accommodate in this container. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.increaseCapacityTo(10);
get
get(key: K): V
Obtains the value of the specified key in this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
key | K | Yes | Target key. |
Return value
Type | Description |
---|---|
V | Value of the key. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.get("sdfs");
getIndexOfKey
getIndexOfKey(key: K): number
Obtains the index of the first occurrence of an element with the specified key in this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
key | K | Yes | Key of the element. |
Return value
Type | Description |
---|---|
number | Returns the position index if obtained; returns -1 otherwise. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getIndexOfKey("sdfs");
getIndexOfValue
getIndexOfValue(value: V): number
Obtains the index of the first occurrence of an element with the specified value in this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
value | V | Yes | Key of the element. |
Return value
Type | Description |
---|---|
number | Returns the position index if obtained; returns -1 otherwise. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getIndexOfValue(123);
getKeyAt
getKeyAt(index: number): K
Obtains the key of an element at the specified position in this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
index | number | Yes | Position index of the element. |
Return value
Type | Description |
---|---|
K | Returns the key if obtained; returns undefined otherwise. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getKeyAt(1);
setAll
setAll(map: LightWeightMap<K, V>): void
Adds all elements in a LightWeightMap instance to this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
map | LightWeightMap<K, V> | Yes | LightWeightMap instance whose elements are to be added to the current container. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let map = new LightWeightMap();
lightWeightMap.setAll(map);
set
set(key: K, value: V): Object
Adds an element to this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
key | K | Yes | Key of the target element. |
value | V | Yes | Value of the target element. |
Return value
Type | Description |
---|---|
Object | Container that contains the new element. |
Example
let lightWeightMap = new LightWeightMap();
let result = lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
remove
remove(key: K): V
Removes an element with the specified key from this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
key | K | Yes | Target key. |
Return value
Type | Description |
---|---|
V | Value of the element removed. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
lightWeightMap.remove("sdfs");
removeAt
removeAt(index: number): boolean
Removes an element at the specified position from this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
index | number | Yes | Position index of the element. |
Return value
Type | Description |
---|---|
boolean | Returns true if the element is removed successfully; returns false otherwise. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.removeAt(1);
setValueAt
setValueAt(index: number, newValue: V): boolean
Sets a value for an element at the specified position in this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
index | number | Yes | Position index of the target element. |
newValue | V | Yes | Value of the target element to set. |
Return value
Type | Description |
---|---|
boolean | Returns true if the value is set successfully; returns false otherwise. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
lightWeightMap.setValueAt(1, 3546);
getValueAt
getValueAt(index: number): V
Obtains the value of an element at the specified position in this container.
System capability: SystemCapability.Utils.Lang
Parameters
Name | Type | Mandatory | Description |
---|---|---|---|
index | number | Yes | Position index of the element. |
Return value
Type | Description |
---|---|
V | Value obtained. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let result = lightWeightMap.getValueAt(1);
clear
clear(): void
Clears this container and sets its length to 0.
System capability: SystemCapability.Utils.Lang
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
lightWeightMap.clear();
keys
keys(): IterableIterator<K>
Obtains an iterator that contains all the keys in this container.
System capability: SystemCapability.Utils.Lang
Return value
Type | Description |
---|---|
IterableIterator<K> | Iterator obtained. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.keys();
let temp = iter.next().value;
while(temp != undefined) {
console.log("value:" + temp);
temp = iter.next().value;
}
values
values(): IterableIterator<V>
Obtains an iterator that contains all the values in this container.
System capability: SystemCapability.Utils.Lang
Return value
Type | Description |
---|---|
IterableIterator<V> | Iterator obtained. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.values();
let temp = iter.next().value;
while(temp != undefined) {
console.log("value:" + temp);
temp = iter.next().value;
}
forEach
forEach(callbackfn: (value?: V, key?: K, map?: LightWeightMap<K, V>) => 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 | 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 | Type | Mandatory | Description |
---|---|---|---|
value | V | No | Value of the element that is currently traversed. |
key | K | No | Key of the element that is currently traversed. |
map | LightWeightMap<K, V> | No | Instance that invokes the forEach method. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("sdfs", 123);
lightWeightMap.set("dfsghsf", 357);
lightWeightMap.forEach((value, key) => {
console.log("value:" + value, key);
});
entries
entries(): IterableIterator<[K, V]>
Obtains an iterator that contains all the elements in this container.
System capability: SystemCapability.Utils.Lang
Return value
Type | Description |
---|---|
IterableIterator<[K, V]> | Iterator obtained. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.entries();
let temp = iter.next().value;
while(temp != undefined) {
console.log("key:" + temp[0]);
console.log("value:" + temp[1]);
temp = iter.next().value;
}
toString
toString(): String
Concatenates the elements in this container into a string and returns the string.
System capability: SystemCapability.Utils.Lang
Return value
Type | Description |
---|---|
String | String obtained. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("A", 123);
lightWeightMap.set("sdfs", 356);
let iter = lightWeightMap.toString();
[Symbol.iterator]
[Symbol.iterator](): IterableIterator<[K, V]>
Obtains an iterator, each item of which is a JavaScript object.
System capability: SystemCapability.Utils.Lang
Return value
Type | Description |
---|---|
IterableIterator<[K, V]> | Iterator obtained. |
Example
let lightWeightMap = new LightWeightMap();
lightWeightMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
lightWeightMap.set("sdfs", 356);
// Method 1:
for (let item of lightWeightMap) {
console.log("key:" + item[0]);
console.log("value:" + item[1]);
}
// Method 2:
let iter = lightWeightMap[Symbol.iterator]();
let temp = iter.next().value;
while(temp != undefined) {
console.log("key:" + temp[0]);
console.log("value:" + temp[1]);
temp = iter.next().value;
}