Author and Book Classes A - An Array of Objects as an Instance Variable in java. Get the Array Objects attributes

Question

Been following this (https://www3.ntu.edu.sg/home/ehchua/programming/java/J3f_OOPExercises.html#zz-2.2) for study java OOP. There is three java file. Now I tested public Author getauthors() {return authors[0]} will return the first author full into: name, email and gender. But I want iterate the authors array to get all the author name only. what should I write in the Books java module?

1. One is pretty simple, used to describe author class. It have three attributes: private String name;private String email;private String gender; the file already tested. All is fine.

2. The Book file to describe the book. One book can have multiple authors.

   public class Book { private String name;private int qty; private double price; Author authors[];

    public Book(String name, int qty, double price) {
        this.name = name; this.qty = qty; this.price = price;}
    public Book(String name, Author authors[], int qty, double price) {
        this.name = name; this.authors = authors;this.qty = qty; this.price = price;}
   
    public String getName() {return name;}
    public void setName(String name) {this.name = name;}
    public double getPrice() {return price;}
    public void setPrice(double price) {this.price = price;}
    public int getQty() {return qty;}
    public void setQty(int qty) {this.qty =qty;}
    public void setauthor(Author[] author) {this.authors = authors;}}
   

3. The third file to test all the methods coded in the first two file.

    public class testauthor {
            public static void main(String[] args) {
            Author[] authorstest = new Author[2];
            authorstest[0] = new Author("Tan Ah Teck", "ahteck@nowhere.com", "m");
            authorstest[1] = new Author("Tyler Cowen", "tcowen@gmu.edu", "M");           
      Book dummyBook = new Book("small steps toward a much better world",authorstest, 19, 99);System.out.println(dummyBook.getName());}}
   

Answer 1

Well, if you want to return the names of all authors, you have to make a choice here:

• Either you return a String[], where each element is the name of one of the authors;

• Or you return a String, where the authors are listed, say, with commas in between. For example: J. He, J. Skeet, M. C. Emperor.

  You could use a for loop for this:

  String authorsText = "";
  for (int i = 0; i < authors.length; i++) {
      if (i > 0) {
          authorsText += ", ";
      }
      authorsText += authors[i].getName();
  }
  

---

Further:

• It is a little peculiar that you can set a book's author after construction. Is the author of a book ever changed after the book is published? The same goes for a book's title. I would have removed those setters, as they don't make sense to me.

Answer 2

you can use stream to get all Names :

Arrays.stream(authors).map(a->a.getName()).collect(Collectors.joining(","));

this get all names and separated by coma