Question

public class LinkedStackOfStrings
{
   private Node first;

   private class Node
   {
      private String item;
      private Node next;
   }

   public boolean isEmpty()
   {  return (first == null); }

   public void push(String item)
   {  // Insert a new node at the beginning of the list.
      Node oldFirst = first;
      first = new Node();
      first.item = item;
      first.next = oldFirst;
   }

   public String pop()
   {  // Remove the first node from the list and return item.
      String item = first.item;
      first = first.next;
      return item;
   }

   public static void main(String[] args)
   {
      LinkedStackOfStrings stack = new LinkedStackOfStrings();
      // See Program 4.3.1 for the test client.
   }
}

first | first node on list

item | stack item
next | next node on list

Modify the “LinkedStackOfStrings.java” program given above (program 4.3.2) by adding a method “find()” that takes a string as an argument. It should return true if the string argument is in the linked stack and false otherwise. [MO6.1]

The main method should also be modified so that all the strings (other than the search string) inputted by the user are stored on the stack before calling the find() method.

• Sample runs would be as follows.
  
  >java LinkedStackOfStrings hello
  this
  is a
  test run
  for the
  hello program
  
  hello exists in the linked stack
  
  >java LinkedStackOfStrings winter
  hello world
  is the first program
  of any programming
  language
  
  winter does not exist in the linked stack

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

// LinkedStackOfStrings.java

import java.util.Scanner;

public class LinkedStackOfStrings {

      private Node first;

      private class Node {

            private String item;

            private Node next;

      }

      public boolean isEmpty() {

            return (first == null);

      }

      public void push(String item) { // Insert a new node at the beginning of the

                                                       // list.

            Node oldFirst = first;

            first = new Node();

            first.item = item;

            first.next = oldFirst;

      }

      public String pop() { // Remove the first node from the list and return

                                           // item.

            String item = first.item;

            first = first.next;

            return item;

      }

      // required method to check if an item exists on stack

      public boolean find(String item) {

            // looping through each node on the stack

            for (Node node = first; node != null; node = node.next) {

                  // checking if node's item equals target item

                  if (node.item.equals(item)) {

                        // found

                        return true;

                  }

            }

            // not found

            return false;

      }

      public static void main(String[] args) {

            LinkedStackOfStrings stack = new LinkedStackOfStrings();

            //if no search string is given, displaying usage and quit

            if(args.length==0){

                  System.out.println("Usage: java LinkedStackOfStrings <word_to_search>");

                  System.exit(0);

            }

            //finding search term

            String searchTerm=args[0];

            //scanner for user input

            Scanner scanner=new Scanner(System.in);

            String input;

            //looping until EOF is triggered (ctrl+D or ctrl+Z)

            while(scanner.hasNext()){

                  //reading next word, adding to stack

                  input=scanner.next();

                  stack.push(input);

            }

            //checking if searchTerm exists

            if(stack.find(searchTerm)){

                  //exists

                  System.out.println(searchTerm+" exists in the linked stack");

            }else{

                  //does not exist

                  System.out.println(searchTerm+" does not exist in the linked stack");

            }

      }

}

/*OUTPUT when ‘hello’ is passed as command line argument*/

this

is a

test run

for the

hello program

hello exists in the linked stack