Java Stack (Stack)

In this tutorial, we will learn about the Java Stack class and its methods through examples.

The Java Collection Framework has a class named Stack, which provides the functionality of the stack data structure.

This Stack class inherits from the Vector class.

Implementation of the stack

In the stack, elements areLast In First Outin the way of storage and access. That is, elements are added to the top of the stack and removed from the top of the stack.

Create a stack

To create a stack, we must first import the java.util.Stack package. After importing the package, we can use Java to create a stack.

Stack<Type> stacks = new Stack<>();

Here, Type indicates the type of the stack. For example,

//Create an integer type stack
Stack<Integer> stacks = new Stack<>();
//Create a string type stack
Stack<String> stacks = new Stack<>();

Stack methods

Since Stack inherits from the Vector class, it inherits all methods of Vector. To learn about different Vector methods, please visitJava Vector Class.

In addition to these methods, the Stack class includes5methods that distinguish it from Vector.

push() method

To add an element to the top of the stack, we use the push() method. For example,

import java.util.Stack;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　Stack<String> animals = new Stack<>();
　　　　　　　　//Add elements to the Stack
　　　　　　　　animals.push("Dog");
　　　　　　　　animals.push("Horse");
　　　　　　　　animals.push("Cat");
　　　　　　　　System.out.println("Stack: ");　+　animals);
　　　　}
}

Output Result

Stack: [Dog, Horse, Cat]

pop() method

To delete an element from the top of the stack, we use the pop() method. For example,

import java.util.Stack;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　Stack<String> animals = new Stack<>();
　　　　　　　　//To add an element to the Stack
　　　　　　　　animals.push("Dog");
　　　　　　　　animals.push("Horse");
　　　　　　　　animals.push("Cat");
　　　　　　　　System.out.println("Initial stack: ");　+　animals);
　　　　　　　　//Delete stack element, following the Last In, First Out (LIFO) principle
　　　　　　　　String element = animals.pop();
　　　　　　　　System.out.println("Delete element: ");　+　element);
　　　　}
}

Output Result

Initial stack: [Dog, Horse, Cat]
Delete element: Cat

peek() method

The peek() method returns an object from the top of the stack. For example,

import java.util.Stack;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　Stack<String> animals = new Stack<>();
　　　　　　　　//Add elements to the Stack
　　　　　　　　animals.push("Dog");
　　　　　　　　animals.push("Horse");
　　　　　　　　animals.push("Cat");
　　　　　　　　System.out.println("Stack: ");　+　animals);
　　　　　　　　//Access element from the top, following the Last In, First Out (LIFO) principle
　　　　　　　　String element = animals.peek();
　　　　　　　　System.out.println("Top element: ");　+　element);
　　　　}
}

Output Result

Stack: [Dog, Horse, Cat]
Top element: Cat

search() method

To search for an element in the stack, we use the search() method. It returns the position of the element from the top of the stack. For example,

import java.util.Stack;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　Stack<String> animals = new Stack<>();
　　　　　　　　//Add elements to the Stack
　　　　　　　　animals.push("Dog");
　　　　　　　　animals.push("Horse");
　　　　　　　　animals.push("Cat");
　　　　　　　　System.out.println("Stack: ");　+　animals);
　　　　　　　　//Search for element
　　　　　　　　int position = animals.search("Horse");
　　　　　　　　System.out.println("The position of element Horse: ");　+　position);
　　　　}
}

Output Result

Stack: [Dog, Horse, Cat]
The position of element Horse:　2

empty() method

To check if the stack is empty, we use the empty() method. For example,

import java.util.Stack;
class Main {
　　　　public static void main(String[] args) {
　　　　　　　　Stack<String> animals = new Stack<>();
　　　　　　　　//Add elements to the Stack
　　　　　　　　animals.push("Dog");
　　　　　　　　animals.push("Horse");
　　　　　　　　animals.push("Cat");
　　　　　　　　System.out.println("Stack: ");　+　animals);
　　　　　　　　//Check if the stack is empty
　　　　　　　　boolean result = animals.empty();
　　　　　　　　System.out.println("Is the stack empty? ");　+　result);
　　　　}
}

Output Result

Stack: [Dog, Horse, Cat]
Is the stack empty? false

Use ArrayDeque instead of Stack

This Stack class provides a direct implementation of the stack data structure. However, it is recommended not to use it. Instead, use the ArrayDeque class (which implements the Deque interface) to implement the stack data structure in Java.

For more information, please visit:Java ArrayDeque