xref: /docs/en/application-dev/reference/apis-arkts/js-apis-hashmap.md (revision e41f4b71)

# @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](js-apis-treemap.md)**, because the former accesses the keys based on the hash codes, whereas the latter stores and accesses the keys in sorted order.

**[HashSet](js-apis-hashset.md)** 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

```ts
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

| 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.

**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](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200012 | The HashMap's constructor cannot be directly invoked. |

**Example**

```ts
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**

| Type | Description |
| -------- | -------- |
| boolean | Returns **true** if the container is empty; returns **false** otherwise. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The isEmpty method cannot be bound. |

**Example**

```ts
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**

| 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. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The hasKey method cannot be bound. |

**Example**

```ts
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**

| 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. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The hasValue method cannot be bound. |

**Example**

```ts
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**

| Name | Type | Mandatory | Description |
| -------- | -------- | -------- | -------- |
| key | K | Yes | Target key. |

**Return value**

| Type | Description |
| -------- | -------- |
| V | Value obtained. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The get method cannot be bound. |

**Example**

```ts
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.

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

**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. |

**Error codes**

For details about the error codes, see [Universal Error Codes](../errorcode-universal.md) and [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 401      | Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types. |
| 10200011 | The setAll method cannot be bound. |

**Example**

```ts
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**

| 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. |

**Error codes**

For details about the error codes, see [Universal Error Codes](../errorcode-universal.md) and [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 401      | Parameter error. Possible causes: 1. Mandatory parameters are left unspecified. |
| 10200011 | The set method cannot be bound. |

**Example**

```ts
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**

| Name | Type | Mandatory | Description |
| -------- | -------- | -------- | -------- |
| key | K | Yes | Key of the target element. |

**Return value**

| Type | Description |
| -------- | -------- |
| V | Value of the element. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The remove method cannot be bound. |

**Example**

```ts
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](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The clear method cannot be bound. |

**Example**

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


### keys

keys(): IterableIterator&lt;K&gt;

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**

| Type | Description |
| -------- | -------- |
| IterableIterator&lt;K&gt; | Iterator obtained. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The keys method cannot be bound. |

**Example**

```ts
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&lt;V&gt;

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**

| Type | Description |
| -------- | -------- |
| IterableIterator&lt;V&gt; | Iterator obtained. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The values method cannot be bound. |

**Example**

```ts
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**

| 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; returns **false** otherwise. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The replace method cannot be bound. |

**Example**

```ts
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.

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

**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 of **this** to use when **callbackFn** is invoked. The default value is this instance. |

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<K, V> | 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](../errorcode-universal.md) and [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 401      | Parameter error. Possible causes: 1. Mandatory parameters are left unspecified; 2. Incorrect parameter types. |
| 10200011 | The forEach method cannot be bound. |

**Example**

```ts
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);
});
```
```ts
// 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&lt;[K, V]&gt;

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**

| Type | Description |
| -------- | -------- |
| IterableIterator&lt;[K, V]&gt; | Iterator obtained. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The entries method cannot be bound. |

**Example**

```ts
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();
}
```
```ts
// 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&lt;[K, V]&gt;

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

> **NOTE**
>
> This API cannot be used in .ets files.

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

**System capability**: SystemCapability.Utils.Lang

**Return value**

| Type | Description |
| -------- | -------- |
| IterableIterator&lt;[K, V]&gt; | Iterator obtained. |

**Error codes**

For details about the error codes, see [Utils Error Codes](errorcode-utils.md).

| ID | Error Message |
| -------- | -------- |
| 10200011 | The Symbol.iterator method cannot be bound. |

**Example**
```ts
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();
 }
```

```ts
// 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);
}
```