Test

Invoice

public class Invoice {
  private String partNumber = "";
  private String partDescription = "";
  private int quantity = 0;
  private double pricePerItem = 0;
  
  public Invoice(String partNumber, String partDescription, int quantity) {
    this.partNumber = partNumber;
    this.partDescription = partDescription;
    this.quantity = quantity;
  }
  
  public Invoice(String partNumber, String partDescription, int quantity, double pricePerItem) {
    this.partNumber = partNumber;
    this.partDescription = partDescription;
    this.quantity = quantity;
    this.pricePerItem = pricePerItem;
  }
  
  public String getPartNumber() {
    return partNumber;
  }
  
  public void setPartNumber(String partNumber) {
    this.partNumber = partNumber;
  }
}

public void main() {
  // Make a new invoice using the default constructor options
  Invoice invoice1 = new Invoice("a1234", "A new item", 2, 1.99);
  
  // Get the part number and store it in a variable
  String szNumber = invoice1.getPartNumber();
  
  // Print out the number
  System.out.println(szNumber);
  
  // Set the part number to something else
  invoice1.setPartNumber("4321a");
  
  // Print out the new part number
  number = invoice1.getPartNumber();
  
  System.out.println(szNumber);
  
  // Fails because of private
  invoice1.partNumber = "a1234567";
  
  // Succeeds because public
  invoice.setPartNumber("a1234567"); 
}