Get Author name from composite class Book

Question

So, I'm new with Object-oriented programming. I have written a code to connect the composite and component class, I need to include at least one method that allows the composite class to communicate with the component class in order to compute some value. But my Book class is not showing the author's name.

This is my code:

public class Author{

private String name;
private String yearOfBirth;  

    public Author ()
    this.name = null;
    this.yearOfBirth = null;   
    }

    public Author (String aName)
    {
       this.name = aName;
       this.yearOfBirth = null;

   }
    public Author(String aName, String     aYear)
    {
  this.name = aName;
  this.yearOfBirth = aYear;
  }

public void setName(String aName)
  {
  this.name = aName;
 }

 public void setYearOfBirth(String aYear)
  {
  this.yearOfBirth = aYear;
 }

    public String getName()
    {
     return this.name;
     }

    public String getYearOfBirth()
     {
      return this.yearOfBirth;
    }  

public String toString()
{
   return this.name + "(Born " + this.yearOfBirth + ")";
}

BOOK CLASS

public class Book
{

 private String title;
 private String yearPublished;
 private Author author;


 public Book(String aTitle, String aYear,Author theAuthor)
  {
    this.title = aTitle;
    this.yearPublished = aYear;
    this.author = theAuthor;
   }


 public Book(String aTitle)
 {
   this.title = aTitle;
   this.yearPublished = null;
   this.author = new Author();
 }

 public void setAuthorName(String aName)
  {
      this.author.setName(aName);
 } 

  public void setYearPublished(String aYear)
  {
     this.yearPublished = aYear;
    }

     public String getTitle()
  {
     return this.title;   
  }

  public String getYearPublished()
   {
    if (this.yearPublished == null)
    {
       return "Unknown";
     }

     return this.yearPublished;
      }

   public String getAuthorName()
   {
     return this.author.getName();
    }

    public boolean isBorn()
    {
         return(Integer.parseInt
   (this.author.getYearOfBirth()) < 1900);
  }

public String toString()
  {

 {
    return "Title: " + this.title + ", Author: " + this.author.getName() + ", yearPublished: " + this.yearPublished+ ".";          
 } 

So when I try and get the author name by doing something like: Book hp = new Book ("Harry Potter","JK Rowling","2000"); it says in the display pane

Compilation failed (20/01/2020 15:02:12)
Error: line 1 - no suitable constructor found for Book(java.lang.String,java.lang.String,java.lang.String)

As you can see, the program does not print the name of the author.

I appreciate all the help!

Answer 1

Because your builder's call is no good.

Book class is waiting to get a title like String , one year of String type

and an Author type author

Example Book book =new Book("test", "2020", new Author("MyAuthor"));

Answer 2

The third parameter which is accepted by the constructor of book is an object of author.

So the invocation should be like

Book hp = new Book ("Harry Potter",2000,new Author("JK Rowling",1965));

Answer 3

As the error message is telling you, you didn't define a constructor for Book that accepts three strings, as you are trying to call it in

Book hp = new Book ("Harry Potter","JK Rowling","2000");

(As a side note, you have author and year backwards)

You have two choices here.

First, you can create the author before calling the Book constructor

Author jkr = new Author("JK Rowling");
Book hp = new Book("Harry Potter", jkr, "2000");

Or you can create a new constructor inside Book that expects the name of the author as a string, builds the author object itself and then calls sets it as the author of the new book

public Book(String title, String author, String year) {
    this.title = title;
    this.author = new Author(author);
    this.yearPublished = year;
}

The first version has the advantage that you can fully utilize your Author class, for example to set the birth year of the author

Author jkr = new Author("JK Rowling", "1965");
Book hp = new Book("Harry Potter", jkr, "2000");

which the second version doesn't allow you to do without creating another constructor which accepts title, author's name, author's birth year, book publication year.