@ohos.util.Stack (Linear Container Stack)

Stack is implemented based on the array data structure. It follows the principle Last Out First In (LOFI) and supports data insertion and removal at one end.

Unlike Queue, which is implemented based on the queue data structure and supports insertion at one end and removal at the other end, Stack supports insertion and removal at the same end.

Recommended use case: Use Stack in LOFI scenarios.

This topic uses the following to identify the use of generics:

T: Type

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 Stack from '@ohos.util.Stack';

Stack

Attributes

System capability: SystemCapability.Utils.Lang

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

constructor

constructor()

A constructor used to create a Stack instance.

System capability: SystemCapability.Utils.Lang

Error codes

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

ID	Error Message
10200012	The Stack's constructor cannot be directly invoked.

Example

let stack : Stack<number|string|Object> = new Stack();

push

push(item: T): T

Adds an element at the top of this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
item	T	Yes	Target element.

Return value

Type	Description
T	Element added.

Error codes

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

ID	Error Message
10200011	The push method cannot be bound.

Example

class C1 {
  name: string = ""
  age: string = ""
}
let stack : Stack<number|string|C1> = new Stack();
let result = stack.push("a");
let result1 = stack.push(1);
let b = [1, 2, 3];
let result2 = stack.push(b);
let c : C1  = {name : "Dylon", age : "13"};
let result3 = stack.push(c);

pop

pop(): T

Removes the top element from this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	Element removed.

Error codes

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

ID	Error Message
10200011	The pop method cannot be bound.

Example

let stack : Stack<number> = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(2);
stack.push(4);
let result = stack.pop();

peek

peek(): T

Obtains the top element of this container.

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
T	Element obtained.

Error codes

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

ID	Error Message
10200011	The peek method cannot be bound.

Example

let stack : Stack<number> = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(2);
let result = stack.peek();

locate

locate(element: T): number

Obtains the index of the first occurrence of the specified element in this container.

System capability: SystemCapability.Utils.Lang

Parameters

Name	Type	Mandatory	Description
element	T	Yes	Target element.

Return value

Type	Description
number	Returns the position index if obtained; returns -1 otherwise.

Error codes

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

ID	Error Message
10200011	The locate method cannot be bound.

Example

let stack : Stack<number> = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(2);
let result = stack.locate(2);

forEach

forEach(callbackFn: (value: T, index?: number, stack?: Stack<T>) => 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 of this to use when callbackFn is invoked. The default value is this instance.

callbackFn

Name	Type	Mandatory	Description
value	T	Yes	Value of the element that is currently traversed.
index	number	No	Position index of the element that is currently traversed. The default value is 0.
stack	Stack<T>	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.

ID	Error Message
10200011	The forEach method cannot be bound.

Example

let stack : Stack<number> = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(4);
stack.forEach((value : number, index ?: number) :void => {
  console.log("value:" + value, "index:" + index);
});

isEmpty

isEmpty(): boolean

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

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.

ID	Error Message
10200011	The isEmpty method cannot be bound.

Example

let stack : Stack<number> = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(4);
let result = stack.isEmpty();

[Symbol.iterator]

[Symbol.iterator](): IterableIterator<T>

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

System capability: SystemCapability.Utils.Lang

Return value

Type	Description
IterableIterator<T>	Iterator obtained.

Error codes

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

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

Example

let stack : Stack<number> = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(4);

// Method 1:
while(!stack.isEmpty()) {
  // Service logic
  let item = stack.pop()
  console.log("value:" + item);
}

// Method 2:
let iter = stack[Symbol.iterator]();
let temp: IteratorResult<number> = iter.next().value;
while(temp != undefined) {
  console.log("value:" + temp);
  temp = iter.next().value;
}