My return stack.get(stack.size-1).getBookName() in my adt class is not working. The line of code is in pop. Whenever I run it and want to remove something from the very top of the stack, it removes the correct thing but doesn't return the correct book removed. Is it the .getBookName() part that is wrong? Please help!

    //main class
import java.util.*;
class Main {
  public static void main(String[] args) {
  Scanner scan=new Scanner (System.in);
  Scanner scanString= new Scanner(System.in);
  int menuInput=0;
  String bookName;
  int pages;
  String author;

  ADT stack=new ADT ();

  while(menuInput!=6)
  {//menu
    System.out.println("1. Add an book to the stack");
    System.out.println("2. Remove an book from the stack");
    System.out.println("3. Return the top book");
    System.out.println("4. Return the length of the stack");
    System.out.println("5. Return if the list is empty");
    System.out.println("6. Exit");
    menuInput=scan.nextInt(); 
    if (menuInput==1)
  {
    System.out.println("What book do you want to add?");
    bookName=scanString.nextLine();
    System.out.println("How many pages are in the book?");
    pages=scan.nextInt();
    System.out.println("Who is the author of the book?");
    author=scanString.nextLine();
    stack.push(bookName, pages, author);
  }
    if (menuInput==2)
    {
      System.out.println(stack.pop());
    }
    if (menuInput==3)
    {
      System.out.println(stack.peek());
    }
    if (menuInput==4)
    {
      System.out.println(stack.length());
    }
    if (menuInput==5)
    {
      System.out.println(stack.isEmpty());
    }
  }

  }
}



    //adt class
import java.util.*;
public class ADT { //ADT stands for Abstract Data Type
String piece;
ArrayList <Book> stack = new ArrayList<Book>();
public ADT(){
  ArrayList <Book> stack = new ArrayList<Book>();
}
public ADT(Book b){
  ArrayList <Book> stack = new ArrayList<Book>();
  stack.add(b);
}
public void push(String bN,int pg, String aut)
{
Book one=new Book(bN,pg,aut);
stack.add(one);
}
public String pop()
{
stack.remove(stack.size()-1);
return "Book removed: "   stack.get(stack.size()-1).getBookName();
}
public String peek()
{
return "First book of the stack: "   stack.get(stack.size()-1).getBookName();
}
public int length()
{
return stack.size();
}
public boolean isEmpty()
{
  if (stack.size()==0)
  return true;
  else
  return false;
}
}



    //book class
public class Book{
  private String bookName;
  //name of the book
  private int pages;
  //pages in the book
  private String author;
  //author of the book
  public Book(String bN,int pg, String aut)//bN=book name, pg=pages, aut=author
  {
    bookName=bN;
    pages=pg;
    author=aut;
  }
  public String getBookName()
  {
    return bookName;
  }
}

CodePudding user response：

You're calling get() after remove(), so it's returning the next last book. If you want the removed book, just use the return value of remove():

public String pop() {
    return "Book removed: "   stack.remove(stack.size()-1).getBookName();
}

CodePudding user response：

The reason this doesn't work is that you're removing the object from the stack, then trying to find it still in the stack. That is, you're calling remove correctly, but then you're calling get on the same stack, which is going to return the next available element if there is one.

Fortunately, the remove method actually returns the object that it removed. So you could write something like

public String pop()
{
    Book removedBook = stack.remove(stack.size()-1);
    return "Book removed: "   removedBook.getBookName();
}