stack data structure 

import java.util.Stack;


public class Main {
    public static void main(String[] args) {
        //create a stack
        Stack<String> stackofbook = new Stack<>();

        //pushing data to the stack
        stackofbook.push("madolduwa");
        stackofbook.push("rumi");

        //to view the stack
        System.out.println(stackofbook);
        //popping data in the stack
        stackofbook.pop();
        stackofbook.pop();
        //peek
        String bookatthetop = stackofbook.peek();
        System.out.println(bookatthetop);

        //check if stack is empty
        System.out.println(stackofbook.empty());


    }
}

        Queue Data Structure (priority)

import java.util.Collection;
import java.util.Collections;
import java.util.PriorityQueue;
import java.util.Queue;

public class queue {
    public static void main(String[] args) {
        //Queue<Double> queue = new PriorityQueue<>();
        //if u wont to reverse order
        Queue<Double> queue = new PriorityQueue<>(Collections.reverseOrder());

        queue.offer(99.8);
        queue.offer(94.4);
        queue.offer(89.5);
        queue.offer(84.33);

        while (!queue.isEmpty()){
            System.out.println(queue.poll());
        }
    }




    }


       Link List Data Structure