Linear Container Stack
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.
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.
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
Example
let stack = 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. |
Example
let stack = new Stack();
let result = stack.push("a");
let result1 = stack.push(1);
let b = [1, 2, 3];
stack.push(b);
let c = {name : "lala", 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. |
Example
let stack = 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. |
Example
let stack = 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. |
Example
let stack = 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 to use when the callback is invoked. |
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. |
stack | Stack<T> | No | Instance that invokes the forEach method. |
Example
let stack = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(4);
stack.forEach((value, index) => {
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. |
Example
let stack = 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. |
Example
let stack = new Stack();
stack.push(2);
stack.push(4);
stack.push(5);
stack.push(4);
// Method 1:
for (let item of stack) {
console.log("value:" + item);
}
// Method 2:
let iter = stack[Symbol.iterator]();
let temp = iter.next().value;
while(temp != undefined) {
console.log("value:" + temp);
temp = iter.next().value;
}