How to code instance variables

• An instance variable may be a primitive data type, an object created from a Java class such as the String class, or an object created from a user-defined class such as the Product class.
• To prevent other classes from accessing instance variables, use the private keyword to declare them as private.

The syntax for declaring instance variables

public|private primitiveType|ClassName variableName;

Examples

private double price;
private int quantity;
private String code;
private Product product;

Where you can declare instance variables

public class Product
{
    //common to code instance variables here
    private String code;
    private String description;
    private double price;

    //the constructors and methods of the class
    public Product(){}
    public void setCode(String code){}
    public String getCode(){ return code; }
    public void setDescription(String description){}
    public String getDescription(){ return description; }
    public void setPrice(double price){}
    public double getPrice(){ return price; }
    public String getFormattedPrice()
        { return formattedPrice; }

    //also possible to code instance variables here
    private int test;
}