Nonlinear Container HashMap

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.

HashMap is a map implemented based on the array, linked list, and red-black tree. It provides efficient data query, insertion, and removal. The elements in a HashMap instance are mappings of key-value pairs. Each key must be unique and have only one value.

HashMap is faster in accessing data than TreeMap, because the former accesses the keys based on the hash codes, whereas the latter stores and accesses the keys in sorted order.

HashSet is implemented based on HashMap. The input parameter of HashMap consists of key and value. In HashSet, only the value object is processed.

Recommended use case: Use HashMap when you need to quickly access, remove, and insert key-value pairs.

Modules to Import

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

HashMap

Attributes

System capability: SystemCapability.Utils.Lang

Name	Type	Readable	Writable	Description
length	number	Yes	No	Number of elements in a hash map (called container later).

constructor

constructor()

A constructor used to create a HashMap instance.

System capability: SystemCapability.Utils.Lang

Example

let hashMap = new HashMap();

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 hashMap = new HashMap();
let result = hashMap.isEmpty();

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 hashMap = new HashMap();
let result = hashMap.hasKey("Ahfbrgrbgnutfodgorrogorgrogofdfdf");
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
let result1 = hashMap.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 hashMap = new HashMap();
let result = hashMap.hasValue(123);
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
let result1 = hashMap.hasValue(123);

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 obtained.

Example

let hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
let result = hashMap.get("sdfs");

setAll

setAll(map: HashMap<K, V>): void

Adds all elements in a HashMap instance to this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
map	HashMap<K, V>	Yes	HashMap instance whose elements are to be added to the current container.

Example

let hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
let newHashMap = new HashMap();
hashMap.setAll(newHashMap);

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 element.

Return value

Type	Description
Object	Container that contains the new element.

Example

let hashMap = new HashMap();
let result = hashMap.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	Key of the target element.

Return value

Type	Description
V	Value of the element.

Example

let hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
let result = hashMap.remove("sdfs");

clear

clear(): void

Clears this container and sets its length to 0.

System capability: SystemCapability.Utils.Lang

Example

let hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
hashMap.clear();

keys

keys(): IterableIterator<K>

Obtains an iterator that contains all the elements in this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<K>	Iterator obtained.

Example

let hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
let iter = hashMap.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 hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
let iter = hashMap.values();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("value:" + temp);
  temp = iter.next().value;
}

replace

replace(key: K, newValue: V): boolean

Replaces an element in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
key	K	Yes	Key of the target element.
newValue	V	Yes	New value of the element.

Return value

Type	Description
boolean	Returns true if the element is replaced successfully; returns false otherwise.

Example

let hashMap = new HashMap();
hashMap.set("sdfs", 123);
let result = hashMap.replace("sdfs", 357);

forEach

forEach(callbackfn: (value?: V, key?: K, map?: HashMap<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	HashMap<K, V>	No	Instance that invokes the forEach method.

Example

let hashMap = new HashMap();
hashMap.set("sdfs", 123);
hashMap.set("dfsghsf", 357);
hashMap.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 hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);
let iter = hashMap.entries();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("key:" + temp[0]);
  console.log("value:" + temp[1]);
  temp = iter.next().value;
}

[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 hashMap = new HashMap();
hashMap.set("Ahfbrgrbgnutfodgorrogorgrogofdfdf", 123);
hashMap.set("sdfs", 356);

// Method 1:
for (let item of hashMap) { 
  console.log("key:" + item[0]);
  console.log("value:" + item[1]);
}

// Method 2:
let iter = hashMap[Symbol.iterator]();
let temp = iter.next().value;
while(temp != undefined) {
  console.log("key:" + temp[0]);
  console.log("value:" + temp[1]);
  temp = iter.next().value;
}