java - Getters and Setters returning null -

i'm trying write simple program produces invoice item purchased. have driver class setters , getters, , object class supposed call them. however, when print out invoice, produces null responses everything.

here driver class:

public class invoice {  private string partnumber;  //part number of item private string description; //description of item private int quantity;       //quantity being purchased private double itemprice;   //price of item  //constructor public invoice(string partnumber, string description, int quantity, double itemprice) {     partnumber = partnumber;     description = description;     if (quantity < 0) {         quantity = 0;     }     if (itemprice < 0.0) {         itemprice = 0.0;     } }  public void setpartnumber(string number) {     partnumber = number; //store partnumber }  public void setdescription(string description) {     description = description;//store description }  public void setquantity(int quantity) {     quantity = quantity;//store quantity }  public void setitemprice(double price) {     itemprice = price;//store itemprice }  public string getpartnumber() {     return partnumber;//retrieve partnumber }  public string getdescription() {     return description;//retrieve description }  public int getquantity() {     return quantity;//retrieve quantity }  public double getitemprice() {     return itemprice;//retrieve itemprice }  //get price item purchased. public double getinvoiceamount(double amount) {     amount = itemprice * quantity;     if (amount < 0) {         amount = 0.0;     }     return amount; } } 

and here object class:

public class invoicetest {  public static void main(string[] args) {     invoice invoice1 = new invoice ("0001", "hammer: used hit nails.", 1, 10.0);      system.out.println("item purchased: " + invoice1.getpartnumber() +             "\n description: " + invoice1.getdescription() +             "\n amount:" + invoice1.getquantity() +             "\n price: " + invoice1.getquantity());     system.out.println();     system.out.println("total price: " + invoice1.getinvoiceamount(amount)); }  } 

you forgot assign variables fields in constructor. use this keyword refer class fields:

public invoice(string partnumber, string description, int quantity, double itemprice) {     //here's example     //partnumber = partnumber     this.partnumber = partnumber;     //description = description;     this.description = description;     //similar other assignments inside constructor... } 

you must in setters well:

public void setpartnumber(string partnumber) {     this.partnumber = partnumber; //store partnumber }