JAVA - Array Stack

 

run:

Element at the top is :8

Element removed is : 8

The size of the stack is : 2

Element removed is : 3

Element at the top is : 9

Stack is empty :  false

BUILD SUCCESSFUL (total time: 0 seconds)

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https://www.scaler.com/topics/java/stack-and-queue-in-java/

 */

package arraystack;

import java.util.*;

public class ArrayStack < E > {

    public static final int CAPACITY = 1000; // default array capacity

    private int topIndex; // index of the top element in the stack

    private E[] data; // generic array used for storage

    

    public ArrayStack() {

        this(CAPACITY);

    } // constructs stack with default capacity

    public ArrayStack(int capacity) { // constructs stack with given capacity

        topIndex = -1;

        data = (E[]) new Object[capacity]; // safe cast; compiler may give warning

    }

    public int size() {

        return (topIndex + 1);

    }

    public boolean empty() {

        return (topIndex == -1);

    }

    public void push(E e) throws IllegalStateException {

        if (size() == data.length) throw new IllegalStateException("Stack is full");

        data[++topIndex] = e; // increment topIndex before storing new item

    }

    public E peek() throws EmptyStackException {

        if (empty()) throw new EmptyStackException();

        return data[topIndex];

    }

    public E pop() throws EmptyStackException {

        if (empty()) throw new EmptyStackException();

        E answer = data[topIndex];

        data[topIndex] = null; // dereference to help garbage collection

        topIndex--;

        return answer;

    }

    public static void main(String args[]) {

        ArrayStack < Integer > mystack = new ArrayStack<>();

        mystack.push(9); //a

        mystack.push(3); //b    

        mystack.push(8); //c 

        System.out.println("Element at the top is :" + mystack.peek()); //d

        System.out.println("Element removed is : " + mystack.pop()); //e

        System.out.println("The size of the stack is : " + mystack.size()); //f

        System.out.println("Element removed is : " + mystack.pop()); //g

        System.out.println("Element at the top is : " + mystack.peek()); //h 

        mystack.push(10); //i

        System.out.println("Stack is empty :  " + mystack.empty()); //j

    /*Note: In output charecters of the comments are written to correspond the 

    output, they won't be printed.*/

    }

}