I´m quite the noob when it comes to coding. I am about to create a programme where you can add the title (String), author (String), release year (int) and genre (String) of a book from writing it in textfields. These things are supposed to be saved in an arraylist. I can not figure out how to add all of these items to the same slot in the arraylist. Please help as fast as possible.
So you need to create a book class with getters/setters.
public class Book {
public String title;
public String author;
public int year;
public String genre;
}
Then you create a Book
Book book = new Book();
use the setters to set the instance variables (or you can do this when creating book object if you have a constructor with appropriate parameters)
book.setAuthor("R.L.Stein");
once all the fields are set you add the book to an array list.
ArrayList<Book> books = new ArrayList<Book>();
books.add(book);
To print, you should have a toString() method in you book class
public String toString(){
return "Title: "+title+"\nAuthor: "+author+"\nYear: "+year+"\nGenre: "+
genre;
}
Now when you print a book object it will show all its information. It's best to then use a loop to iterate through the list and print each book in books
for(int i=0; i<books.size(); i++){
System.println(books.get(i));
}
Building off of my comment in the original post, here's what your book class should look like:
public class Book {
private String title;
private String author;
private String genre;
private int releaseYear;
public Book(String title, String author, String genre, int releaseYear) {
this.title = title;
this.author = author;
this.genre = genre;
this.releaseYear = releaseYear;
}
public String getTitle() { return this.title; }
public String getAuthor() { return this.author; }
public String getGenre() { return this.genre; }
public int getReleaseYear() { return this.releaseYear; }
}
Now all you need to do is create multiple instances of these classes, and add them into your ArrayList.
Here's a link with some examples of how to use ArrayLists: http://beginnersbook.com/2013/12/how-to-initialize-an-arraylist/
You can do this in two ways.
Create a class containing the title (String), author (String), release year (int) and genre (String) and create a new instance of that class and add it to the array. Here is a javadoc on classes.
(Not recommended, but still works) You can create an array list with a size of 4. The array will be an Object to support the integer. Example: Object[] obj = new Object[]{"title", "author", 2015, "genre"}; You can then take the array and add it to the other array you wanted to add this information to.
If you want to go with choice two and create a class here is an example:
public class Book {
private String title, author, genre;
private int releaseYear;
public Book(String title, String author, int releaseYear, String genre){
this.title = title;
this.author = author;
this.releaseYear = releaseYear;
this.genre = genre;
}
public String getTitle() {
return title;
}
public String getAuthor() {
return author;
}
public String getGenre() {
return genre;
}
public int getReleaseYear() {
return releaseYear;
}
public void setTitle(String title) {
this.title = title;
}
public void setAuthor(String author) {
this.author = author;
}
public void setGenre(String genre) {
this.genre = genre;
}
public void setReleaseYear(int releaseYear) {
this.releaseYear = releaseYear;
}
}
If you wanted to create a new instance of the Book class you would do:
Book book = new Book("title", "author", 2015, "genre");
Related
I'm new to Java and currently I'm learning constructor. So I have a Person class
class Person {
private String name;
private double height;
Person(String name, double height) {
this.name = name;
this.height = height;
}
}
and a Book class
public class Book {
private String author;
private String title;
public Raamat(String author, String title) {
this.author = author;
this.title = title;
}
}
and a Test class
public class TestBook {
public static void main(String[] args) {
Book harryp = new Book("Rouling", "Harry Potter");
}
}
My task is to change Book class, so that author is Person-type instead of String-type like this:
private String author --> private Person author
So the Book class will look like this:
public class Book {
private Person author;
private String title;
public Book(String author, String title) {
this.author = author;
this.title = title;
}
}
So basically it should get author's name from Person's constructor? Or how does it work? And how should I modify Test class for it to work?
You'll have to initialize the Person object first.
Person author = new Person("foo", 100d);
Then you can change the Book class as follow:
public class Book {
private Person author;
private String title;
public Book(Person author, final String title) {
this.author = author;
this.title = title;
}
}
And finally initialize the Book object as follows:
Person author = new Person("foo", 100d);
Book b = new Book(author, "My Title");
Solution 1:
public class Book {
private Person author;
private String title;
public Book(String author, String title) {
this.author = new Person(author);
this.title = title;
}
}
class Person {
private String name;
private double height;
public static final double DEFAULT_HEIGHT = 0.0;
Person(String name, double height) {
this.name = name;
this.height = height;
}
Person(String name) {
this(name, DEFAULT_HEIGHT);
}
}
You have to add one more constructor into your Person class, and instantate a new Person when you pass String author into Book
Book b = new Book("Mike", "Book Title");
Alternatively, pass person instance into Book and access name by getName():
public class Book {
private Person author;
private String title;
public Book(Person author, String title) {
this.author = author.getName();
this.title = title;
}
}
So basically it should get author's name from Person's constructor?
Not necessarily. You can keep the client code simple by creating the Person directly in the Book constructor.
public class Book {
private Person author;
private String title;
public Book(String authorName, double height, String title) {
this.author = new Person(authorName, height);
this.title = title;
}
}
You would call it :
Book book = new Book("author", 170, "book title");
Yon can also accept a Person as parameter in the constructor :
public Book(Person author, String title) {
this.author = author;
this.title = title;
}
And in this case, the client code should pass a Person and not a String and a double.
Person author = new Person("author", 170)
Book book = new Book(author, "book title");
You can even propose both by overloading the constructor.
In fact, the way that you should use is the way that is the most practical for the class clients.
author should be a new Person, whose name is drawn from the name field of Book's constructor.
There are two ways you can solve this:
By changing the parameter type on your constructor to Person:
public class Book {
private Person author;
private String title;
public Raamat(Person author, String title) {
this.author = author;
this.title = title;
}
}
By initializing the author on the constructor:
public class Book {
private Person author;
private String title;
public Raamat(String author, String title) {
this.author = new Person(author);
this.title = title;
}
}
I am getting an error saying my constructor Book(String, int) is undefined in my Dictionary class. I check everything else and try to redo my programs still has an error. Any solutions of fixing this issue?
Book Class:
public class Book{
private String author;
private int numPages;
public Book(int code, String title, double price, int quantity, String author, int numPages){
this.author = author;
this.numPages = numPages;
}
//Getters
public String getAuthor(){
return this.author;
}
public int getNumPages(){
return this.numPages;
}
//Setters
public void setAuthor(String author){
this.author = author;
}
public void setNumPages(int numPages){
this.numPages = numPages;
}
//toString
#Override
public String toString(){
String outputBookDes = "";
outputBookDes += "Author: "+ this.author;
outputBookDes += "Number Pages: "+ this.numPages;
return outputBookDes;
}
}
Dictionary Class:
public class Dictionary extends Book{
private String language;
private int numDefinitions;
public Dictionary(String author, int numPages, String language, int numDefinitions){
super(author,numPages);
this.language = language;
this.numDefinitions = numDefinitions;
}
// Getters
public String getLanguage(){
return this.language;
}
public int getNumDefinitions(){
return this.numDefinitions;
}
//Setters
public void setLanguage(String language){
this.language = language;
}
public void setNumDefinitions(int numDefinitons){
this.numDefinitions = numDefinitions;
}
//Ratio method
public double getRatio(){
double ratioTotal = this.numDefinitions / getNumPages();
return ratioTotal;
}
}
As you are calling
super(author,numPages);
in child class Dictionary,
you need to define another constructor in Book class like,
public Book(String author,int numPages) {
this.author = author;
this.numPages = numPages;
}
to get this error solved.
according to your only constructor:
public Book(int code, String title, double price, int quantity, String author, int numPages)
In your main method try:
Book book = new Book(12, "title", 34d, 56, "author", 78);
instead of:
Book book = new Book("34", 56);
Having trouble creating an author object in the Book class.This is indeed Homework, I have came up with all the methods on my own and have been staring at this assignment for 2 hours now. any tips hints will be appreciated. I believe I am only allowed this one Author constructor with 3 parameters otherwise I would just have made an Author constructor with no arguments and the problem would be gone.
public class Author {
protected String name;
protected String email;
protected char gender;
public Author(String name, String email, char gender)
{
this.name = name;
this.email = email;
this.gender = gender;
}
public String getName()
{
return name;
}
public String getEmail()
{
return email;
}
public void setEmail(String email)
{
this.email = email;
}
public char getGener()
{
return gender;
}
public String toString()
{
return ( name + "(" + gender + ")#" + email);
}
}
public class Book extends Author{
private String name;
private Author author;
private double price;
private int qtyInStock = 0;
public Book(String name, Author author,Double price)
{
this.author = new author;
this.name = name;
this.price = price;
}
public Book(String name, Author author, double price, int qtyInStock)
{
this.name = name;
this.author = author;
this.price = price;
this.qtyInStock = qtyInStock;
}
public String getName()
{
return name;
}
public Author getAuthor()
{
return author;
}
public double getPrice()
{
return price;
}
public void setPrice(double price)
{
this.price = price;
}
public int getQtyInStock()
{
return qtyInStock;
}
public void setQtyInStock(int qtyInStock)
{
this.qtyInStock = qtyInStock;
}
public String toString()
{
return (name + " by " + author + "(" + super.gender + ")at" + super.email);
}
}
It should be this.author = author; without the new keyword.
You are assigning the Author object in the constructor, not creating new one.
By the way, Book inherits from Author which means it already has the Author functionality. You don't have to save it as member.
Seems strange that Book extends Author. A Book is not an Author.
I think what you want to do is create a Book object that has an Author, but you are already passing in an Author to your Book constructor, so what is the problem?
class Book {
public Book(String title, Author author) {
this.title = title;
this.author = author;
}
}
If you're wondering how to create the Author, just create it before you pass it to the Book.
Author author = new Author("bob", "bob#email.com", 'm');
Book book = new Book("some title", author);
Does that make sense?
You are inheriting Author in Book, inheritance is is a relationship, means Book is a Author which is not true in real world scenario , you need has a relation which makes sense , that Book has a Author.
So don't extend author in Book , keep a field of author in it as you have already did. Change you design.
There are multiple mistakes in your code:
as #Guy said, you need to assign the author with this.author = author, without the new keyword.
you are shadowing the name variable from the Author class by also including a variable with the same name in the Book class. Remove that variable and the getter and setter methods from the Book class.
You don´t have a no parameter constructor, so you have to call the parent constructor in your Book class by calling super(name, email, gender);.
you should replace new author with author, also when you call the constructor of a sub Type, the Parent class's default constructor is invoked by default. so you need to specify a default constructor in your parent class, or to prevent this explicitly call your parametric constructor of parent class in the child class constructor .
Besides changing tothis.author = author.
You also need to add super(name, name, 'M'); to the two constructors of the Book class.
public class Book extends Author{
private String name;
//private final String email;
// private char gender;
private Author author;// = new Author(name,super.email,super.gender);
private double price;
private int qtyInStock = 0;
public Book(String name, Author author,double price)
{
//super();
this.author = author;// new Author(name,super.email,super.gender);
super.name = author.getName();
super.gender = author.getGender();
super.email = author.getEmail();
this.name = name;
this.price = price;
}
public Book(String name, Author author, double price, int qtyInStock)
{
this.author = author;
super.name = author.getName();
super.gender = author.getGender();
super.email = author.getEmail();
this.name = name;
this.price = price;
this.qtyInStock = qtyInStock;
}
public String getName()
{
return name;
}
public Author getAuthor()
{
return author;
}
public double getPrice()
{
return price;
}
public void setPrice(double price)
{
this.price = price;
}
public int getQtyInStock()
{
return qtyInStock;
}
public void setQtyInStock(int qtyInStock)
{
this.qtyInStock = qtyInStock;
}
public String toString()
{
return (super.name + " by " + this.name + "(" + super.gender + ")at" + super.email);
}
also added this to the author class
public Author()
{
}
This question already has answers here:
Java string returns as null
(4 answers)
Closed 7 years ago.
I have just started learning java and I was given a pretty simple assignment on constructors and instances. For some reason my instances are not being set when they are created and only when I call the set methods. Can you please help me out I've been stuck for a while now with no where to go.
package hka437documents;
/**
*
* #author Henry
*/
public class Hka437Documents{
public static class Documents {
/**
* #param args the command line arguments
*/
private String title;
private String author;
private String body;
private int version;
public Documents(String title, String author){
version = 0;
}
public Documents(String title, String author, String body){
version = 1;
}
public void setTitle(String title){
this.title = title;
version++;
}
public void setAuthor(String author){
this.author = author;
}
public void setBody(String body){
this.body = body;
version++;
}
public String getTitle(){
return title;
}
public String getAuthor(){
return author;
}
public String getBody(){
return body;
}
public int getVersion(){
return version;
}
}
public static void main(String[] args) {
Documents document1 = new Documents("Another Life", "Sally Smith");
document1.setBody("The grass is always greener on the other side.");
Documents document2 = new Documents("Final Word", "Karen Jones", "We should plan for the worst and hope for the best.");
document2.setTitle("Final Words");
System.out.println("document1:");
System.out.println("Title: "+ document1.getTitle());
System.out.println("Author: "+ document1.getAuthor());
System.out.println("Body: "+ document1.getBody());
System.out.println("Version: "+ document1.getVersion());
System.out.println("\ndocument2:");
System.out.println("Title: "+ document2.getTitle());
System.out.println("Author: "+ document2.getAuthor());
System.out.println("Body: "+ document2.getBody());
System.out.println("Version: "+ document2.getVersion());
}
}
When I run the program I get null on the print statements for all of them except for the document1+2 version, document1 body and document2 title. These are the ones that had variables set with the set methods.
Look here:
public Documents(String title, String author){
version = 0;
}
public Documents(String title, String author, String body){
version = 1;
}
Your constructors only initialize version.
You have to add:
this.title = title;
this.author = author;
in the first, and:
this.title = title;
this.author = author;
this.body = body;
In the second.
you have to set atributes with params values in the constructor:
public Documents(String title, String author){
version = 0;
this.title = title;
this.author = author;
}
public Documents(String title, String author, String body){
version = 1;
this.title = title;
this.author = author;
this.body= body;
}
You actually want to set the fields in the constructor, they won't just be copied by magic. Right now they are just being ignored. You'd want a change like the following in both constructors:
this.title = title;
this.author = author;
You also want something similar to set body as well.
this.body = body;
in this program i need to add 4 books to a library.The code is for my book class but i need to make a method with 4 arguments in another file in my library class that will add the books into a library array.There is a third file for the main where i will print this all out but i just cant figure this out.
Example of book: author-clowney, title-individualism,price-5.50,isbn-978-52-234-43-012
private String author;
private String title;
private double price;
private int isbn;
public book(String a, String t, double p, int i){
author=a;
title=t;
price=checkPrice(p);
isbn=checkIsbn(i);
}
//First and foremost you need to create the book object
public class Book extends Library{
private String author;
private String title;
private double price;
private int isbn;
//Null Constructor-this creates
public book() {
this.author = abcd;
this.title = abcd;
this.price = 0.0;
this.isbn = 0000000;
}
//Now its time for the book with parameters
public book(String a, String t, double p, int i){
author = a;
title = t;
price = p;
isbn = i;
}
//Now it's time to set and get the above values you want
public void setAuthor(String author){
this.author = author;
}
public String getAuthor(){
return this.author;
}
public void setTitle(String title){
this.title = title;
}
public String getTitle(){
return this.title;
}
public void setPrice(double price){
this.price = price;
}
public double getPrice(){
return this.price;
}
public void setIsbn(int isbn){
this.isbn = isbn;
}
public double getIsbn(){
return this.isbn;
}
//Now you are going to want to toString(), that way you can display the books in the library
public String toString() {
//Im assuming you have learned that Library is your super class and has a toString() as well
return(super.toString()+ "Book Author: " + this.author + "Book Title: " + this.title + "Book Price: " + this.price + "Book ISBN: " + this.isbn);
}
}
//Now simply call this method within your main method to display books in Output!!
//Hope this helps, if you have further questions please leave below!!