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A stack is a linear dynamic data structure that follows Last-In/First-Out (LIFO) principle. In a stack, addition of a new element and deletion of an element occurs at the same end which implies that the element which is added last in the stack will be the first to be removed from the stack.

Features of stack

  • It is a dynamic data structure.
  • It has dynamic size.
  • It uses dynamic memory allocation.

Operations of a stack

  • isEmpty(): Checks whether the stack is empty or not.
  • size(): Returns the size of the stack.
  • topElement(): Returns the top element of the stack.
  • push(x): Adds a new element ‘x’ at the top of the stack. Consequently, size of the stack increases by 1.
  • Stack Push
  • pop(): Deletes the top element of the stack. Consequently, size of the stack decreases by 1.
  • Stack Pop

Implementation of Stack

class CreateStack {
  static final int MAX = 100;
  int top;
  //assigning MAX size of the stack
  int stack[] = new int[MAX];

  CreateStack() {
    top = -1;
  }

  // create a method to check whether 
  // the stack is empty or not  
  void isEmpty() {
    if(top == -1) {
      System.out.println("Stack is empty.");
    } else {
      System.out.println("Stack is not empty.");
    }
  }

  //create a method to return size of the stack 
  int size() {
     return top+1;
  } 

  //create a method to add new element       
  void push(int x){
    if(top == (MAX - 1)){
      System.out.println("Stack size limit reached.");
    } else {
      stack[++top] = x;
      System.out.println(x + " is added into the stack.");
    }
  }

  //create a method to delete top element       
  void pop(){
    if(top < 0){
      System.out.println("Stack is empty.");
    } else {
      int x = stack[top--];
      System.out.println(x + " is deleted from the stack.");
    }
  }  

  //create a method to get top element       
  int topElement() {
    if(top < 0) {
      System.out.println("Stack is empty.");
      return 0;
    } else {
      return stack[top];
    }
  }
}

// test the code
public class MyClass {
  public static void main(String[] args) {
    CreateStack MyStack = new CreateStack();
    MyStack.push(10);
    MyStack.push(20);
    MyStack.push(30);
    MyStack.push(40);

    MyStack.pop();
    MyStack.isEmpty(); 
  }
}

The above code will give the following output:

10 is added into the stack.
20 is added into the stack.
30 is added into the stack.
40 is added into the stack.
40 is deleted from the stack.
Stack is not empty.