@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 '@ohos.util.HashMap'; 

HashMap

Attributes

System capability: SystemCapability.Utils.Lang

constructor

constructor()

A constructor used to create a HashMap instance.

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).

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.

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.

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.

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.

System capability: SystemCapability.Utils.Lang

Parameters

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 newHashMap: HashMap<string, number> = new HashMap();
newHashMap.set("newMap", 99);
hashMap.setAll(newHashMap);

set

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

Adds an element to this container.

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();
let result = hashMap.set("squirrel", 123);

remove

remove(key: K): V

Removes an element with the specified key from this container.

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.

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.

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.

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.

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.

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 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);
});

entries

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

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

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();
}

[Symbol.iterator]

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

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

NOTE

This API cannot be used in .ets files.

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().value;
while(temp != undefined) {
  console.log("key:" + temp[0]);
  console.log("value:" + temp[1]);
  temp = iter.next().value;
}

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