harmony 鸿蒙@ohos.util.HashMap (Nonlinear Container HashMap)

2022-08-09 浏览 (861)

@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

NameTypeReadableWritableDescription
lengthnumberYesNoNumber of elements in a hash map (called container later).

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.

IDError Message
10200012The HashMap's constructor cannot be directly invoked.

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

TypeDescription
booleanReturns true if the container is empty; returns false otherwise.

Error codes

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

IDError Message
10200011The isEmpty method cannot be bound.

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

NameTypeMandatoryDescription
keyKYesTarget key.

Return value

TypeDescription
booleanReturns true if the specified key is contained; returns false otherwise.

Error codes

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

IDError Message
10200011The hasKey method cannot be bound.

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

NameTypeMandatoryDescription
valueVYesTarget value.

Return value

TypeDescription
booleanReturns true if the specified value is contained; returns false otherwise.

Error codes

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

IDError Message
10200011The hasValue method cannot be bound.

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

NameTypeMandatoryDescription
keyKYesTarget key.

Return value

TypeDescription
VValue obtained.

Error codes

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

IDError Message
10200011The get method cannot be bound.

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<K, V>): void

Adds all elements in a HashMap instance to this container.

System capability: SystemCapability.Utils.Lang

Parameters

NameTypeMandatoryDescription
mapHashMap<K, V>YesHashMap instance whose elements are to be added to the current container.

Error codes

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

IDError Message
10200011The setAll method cannot be bound.

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

NameTypeMandatoryDescription
keyKYesKey of the target element.
valueVYesValue of the target element.

Return value

TypeDescription
ObjectContainer that contains the new element.

Error codes

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

IDError Message
10200011The set method cannot be bound.

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

NameTypeMandatoryDescription
keyKYesKey of the target element.

Return value

TypeDescription
VValue of the element.

Error codes

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

IDError Message
10200011The remove method cannot be bound.

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.

IDError Message
10200011The clear method cannot be bound.

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

TypeDescription
IterableIterator<K>Iterator obtained.

Error codes

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

IDError Message
10200011The keys method cannot be bound.

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

TypeDescription
IterableIterator<V>Iterator obtained.

Error codes

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

IDError Message
10200011The values method cannot be bound.

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

NameTypeMandatoryDescription
keyKYesKey of the target element.
newValueVYesNew value of the element.

Return value

TypeDescription
booleanReturns true if the element is replaced successfully; returns false otherwise.

Error codes

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

IDError Message
10200011The replace method cannot be bound.

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<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

NameTypeMandatoryDescription
callbackFnfunctionYesCallback invoked to traverse the elements in the container.
thisArgObjectNoValue of this to use when callbackFn is invoked. The default value is this instance.

callbackFn

NameTypeMandatoryDescription
valueVNoValue of the element that is currently traversed. The default value is the value of the first key-value pair.
keyKNoKey of the element that is currently traversed. The default value is the key of the first key-value pair.
mapHashMap<K, V>NoInstance that calls the forEach API. The default value is this instance.

Error codes

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

IDError Message
10200011The forEach method cannot be bound.

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

TypeDescription
IterableIterator<[K, V]>Iterator obtained.

Error codes

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

IDError Message
10200011The entries method cannot be bound.

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

TypeDescription
IterableIterator<[K, V]>Iterator obtained.

Error codes

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

IDError Message
10200011The Symbol.iterator method cannot be bound.

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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