A question by a beginner

Question

Hi All, i'm a beginner and i'm studing on a book the foundamental of Java. I have followed the book and i have write my first scripts that is:
* SimpleCar.java
* Created on February 4, 2007, 2:04 PM
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
* @author Emanuele Mignosa
public class SimpleCar {
private String manufacturer = "Sconosciuto";
private String color = "Bianco";
private double miles = 0;
private final double KMTOMILE = 0.62137;
private final double MILETOKM = 1.60934;
public String getManufacturer() {
return manufacturer;
public void setManufacturer(String manufacturer) {
this.manufacturer = manufacturer;
public String getColor() {
return color;
public void setColor(String color) {
this.color = color;
public double getMiles() {
return miles;
public void setMiles(double miles) {
this.miles = miles;
public void drive (double kilometres){
this.miles += Math.round(
(kilometres * KMTOMILE)*100.)/100.;
public double getKilometres(long miles){
return Math.round((miles * MILETOKM)*100.)/100.;
public String carStatus() {
String status = "old";
if (this.getMiles()<= 10) {
status = "very new";
else if(this.getMiles()<= 1000){
status = "new";
else if(this.getMiles()<= 10000){
status = "almost new";
else if(this.getMiles()<= 20000){
status = "in perfect conditions";
else if(this.getMiles()<= 50000){
status = "used";
else if(this.getMiles()<= 150000){
status = "old";
return status;
and a next script that invoke the class SimpleCar that is :
[public class SimpleCarInvoker {
     /** Creates a new instance of SimpleCarInvoker */
    public static void main (String[] args){
SimpleCar car = new SimpleCar();
car.setManufacturer("Audi");
car.setColor("blu");
car.drive(10000);
System.out.println (String.format(
"You are driven a %s %s that has this condition : %s",
car.getManufacturer(),
car.getColor(),
car.carStatus()));
untill this point all perfect
the book advices this script :
[public class SimpleCar{
    private String manufacturer = "Sconosciuto";
    private String color = "Bianco";
    private double miles = 0;
    private final double KMTOMILE = 0.62137;
    private final double MILETOKM = 1.60934;
    /** Creates a new instance of SimpleCar1*/
    public SimpleCar() {
        this.setManufacturer("Porche");
        this.setColor("Blu");
public SimpleCar(String manufacturer) {
this();
this.setManufacturer(manufacturer);
public SimpleCar(double miles) {
this();
this.setMiles(miles);
public SimpleCar(String manufacturer, double miles) {
this.setManufacturer(manufacturer);
this.setMiles(miles);
public SimpleCar(String manufacturer, String color) {
this.setManufacturer(manufacturer);
this.setColor(color);
public SimpleCar(String manufacturer, String color, double miles) {
this.setManufacturer(manufacturer);
this.setColor(color);
this.setMiles(miles);
I have delete the old java class, and i have created a new java class with the same name, as i see on the book, but there were many problems and i don't know what i must change.
Thanks a lot in advance
Emanuele
P.S i think there is a error in the book, because the new scripts don't create the metod "set", or i must put insert the new script in the old script, but class is the same.

Answer 1

I'm not sure if this will do it. That's a lot of code to sort through.
Before the change, you didn't have any constructors. Now you're adding them in. So if you have Strings as instance variables, a constructor won't be able to change them.
Try just saying private String manufacturer; at the beginning.
instead of keeping the " ='Sconosciuto' " part. Strings are pointers and they cannot be reset.
I've never seen a book use setter methods to set the variables. If you haven't defined your variable manufacturer yet, you should be able to just say inside your constructor:
manufacturer = "Audi", e.g.
Hope it helps