@ohos.util.HashMap (Nonlinear Container HashMap)

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.

This topic uses the following to identify the use of generics: - K: Key - V: Value

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 { HashMap } from '@kit.ArkTS';

HashMap

Attributes

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

constructor

constructor()

A constructor used to create a HashMap instance.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();

isEmpty

isEmpty(): boolean

Checks whether this container is empty (contains no element).

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

const hashMap: HashMap<string, number> = new HashMap();
let result = hashMap.isEmpty();

hasKey

hasKey(key: K): boolean

Checks whether this container contains the specified key.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

const hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
let result = hashMap.hasKey("squirrel");

hasValue

hasValue(value: V): boolean

Checks whether this container contains the specified value.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

const hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
let result = hashMap.hasValue(123);

get

get(key: K): V

Obtains the value of the specified key in this container. If nothing is obtained, undefined is returned.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

const hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
let result = hashMap.get("sparrow");

setAll

setAll(map: HashMap): void

Adds all elements in a HashMap instance to this container.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Error codes

For details about the error codes, see Universal Error Codes and Utils Error Codes.

Example

const hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
let newHashMap: HashMap<string, number> = new HashMap();
newHashMap.set("newMap", 99);
hashMap.setAll(newHashMap);

set

set(key: K, value: V): Object

Adds or updates an element in this container.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Universal Error Codes and Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
let result = hashMap.set("squirrel", 123);

remove

remove(key: K): V

Removes an element with the specified key from this container.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
let result = hashMap.remove("sparrow");

clear

clear(): void

Clears this container and sets its length to 0.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
hashMap.clear();

keys

keys(): IterableIterator<K>

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

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
let iter = hashMap.keys();
let temp: IteratorResult<string,number> = iter.next();
while(!temp.done) {
  console.log("value:" + temp.value);
  temp = iter.next();
}

values

values(): IterableIterator<V>

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

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
let iter = hashMap.values();
let temp: IteratorResult<number> = iter.next();
while(!temp.done) {
  console.log("value:" + temp.value);
  temp = iter.next();
}

replace

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

Replaces an element in this container.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("sparrow", 123);
let result = hashMap.replace("sparrow", 357);

forEach

forEach(callbackFn: (value?: V, key?: K, map?: HashMap) => void, thisArg?: Object): void

Uses a callback to traverse the elements in this container and obtain their position indexes.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Parameters

callbackFn |Name|Type|Mandatory|Description| |——–|——–|——–|——–| |value|V|No|Value of the element that is currently traversed. The default value is the value of the first key-value pair.| |key|K|No|Key of the element that is currently traversed. The default value is the key of the first key-value pair.| |map|HashMap|No|Instance that calls the forEach API. The default value is this instance.|

Error codes

For details about the error codes, see Universal Error Codes and Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("sparrow", 123);
hashMap.set("gull", 357);
hashMap.forEach((value?: number, key?: string) => {
  console.log("value:" + value, "key:" + key);
});

// You are not advised to use the set or remove APIs in forEach because they may cause unpredictable risks such as infinite loops. You can use the for loop when inserting or deleting data.
let hashMap: HashMap<string, number> = new HashMap();
for(let i = 0; i < 10; i++) {
  hashMap.set("sparrow" + i, 123);
}

for(let i = 0; i < 10; i++) {
  hashMap.remove("sparrow" + i);
}

entries

entries(): IterableIterator<[K, V]>

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

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);
let iter = hashMap.entries();
let temp: IteratorResult<Object[]> = iter.next();
while(!temp.done) {
  console.log("key:" + temp.value[0]);
  console.log("value:" + temp.value[1]);
  temp = iter.next();
}

// You are not advised to use the set or remove APIs in entries because they may cause unpredictable risks such as infinite loops. You can use the for loop when inserting or deleting data.
let hashMap: HashMap<string, number> = new HashMap();
for(let i = 0; i < 10; i++) {
  hashMap.set("sparrow" + i, 123);
}

for(let i = 0; i < 10; i++) {
  hashMap.remove("sparrow" + i);
}

[Symbol.iterator]

[Symbol.iterator](): IterableIterator<[K, V]>

Obtains an iterator, each item of which is a JavaScript object.

Atomic service API: This API can be used in atomic services since API version 12.

System capability: SystemCapability.Utils.Lang

Return value

Error codes

For details about the error codes, see Utils Error Codes.

Example

let hashMap: HashMap<string, number> = new HashMap();
hashMap.set("squirrel", 123);
hashMap.set("sparrow", 356);

// Method 1:
let keys = Array.from(hashMap.keys());
for (let key of keys) {
  console.log("key:" + key);
  console.log("value:" + hashMap.get(key));
}

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

// You are not advised to use the set or remove APIs in Symbol.iterator because they may cause unpredictable risks such as infinite loops. You can use the for loop when inserting or deleting data.
let hashMap: HashMap<string, number> = new HashMap();
for(let i = 0; i < 10; i++) {
  hashMap.set("sparrow" + i, 123);
}

for(let i = 0; i < 10; i++) {
  hashMap.remove("sparrow" + i);
}

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