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Java Stack


What is Stack ?

Stack is a linear data structure which follows a particular order in which the operations are performed. The order may be LIFO(Last In First Out) or FILO(First In Last Out). Mainly the following three basic operations are performed in the stack :

Push: Adds an item in the stack. If the stack is full, then it is said to be an Overflow condition.

Pop: Removes an item from the stack. The items are popped in the reversed order in which they are pushed. If the stack is empty, then it is said to be an Underflow condition.

Peek or Top: Returns top element of stack.

isEmpty: Returns true if stack is empty, else false.

Example :-

import java.util.*;

public class JavaStackDemo {
  public static void main(String[] args)
  {
  //Create an empty Stack
  Stack stack = new Stack();
  
  System.out.println("After Push Operation on Stack :");
  stack.push("first");
  printStackElements(stack);
  stack.push("second");
  printStackElements(stack);
  stack.push("third");
  printStackElements(stack);
  
  System.out.println("\nAfter Pop Operation on Stack :");
  stack.pop();
  printStackElements(stack);
  stack.pop();
  printStackElements(stack);
  stack.pop();
  printStackElements(stack);
  
  
  }
  
  private static void printStackElements(Stack stack)
  {
    if(stack.isEmpty())
    {
      System.out.println("No more items left on the stack");
    }
    else
    {
      System.out.printf("%s\n", stack);
    }
  }
}

Output :-

After Push Operation on Stack :
[first]
[first, second]
[first, second, third]

After Pop Operation on Stack :
[first, second]
[first]
No more items left on the stack