Attributes
- Java course
- Intermediate
- Lesson 2/116
- 4 min
Learn class and instance attributes.
Attributes: fields
The variables that hold a class's data are called fields. Each field is declared with a type and a name. The type determines what values the field can store; for example int for integers, double for decimals, String for text.
Example: class Product { String name; double price; int stock; }. Here three fields exist: name is a string, price a decimal, stock an integer. Before you assign a value, fields get defaults: numeric fields start at zero, string fields at null.
Assigning values to fields
You access an instance's field with a dot: object.field. Assignment uses the = sign. First create the instance with new, then assign values to its fields.
Example: Product p = new Product(); p.name = "Pen"; p.price = 12.5;. Here p is a Product instance. p.name accesses the name field and assigns a value. The instance must be created before assignment; otherwise you get an error.
Practice Define the Product class
Define a class named Product. Add three fields: String name, double price, int stock. In main create a Product instance, assign values to all three fields and print name and price on separate lines.
Starter code
// Define the Product class
// Add three fields
// Instantiate and print in mainSample solution
class Product {
String name;
double price;
int stock;
public static void main(String[] args) {
Product p = new Product();
p.name = "Notebook";
p.price = 25.0;
p.stock = 10;
System.out.println(p.name);
System.out.println(p.price);
}
}Expected output
Notebook 25.0
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match field types
| Term | Meaning |
|---|---|
int |
Integer |
double |
Decimal |
String |
Text |
boolean |
Logical |
2 How do you assign 9.99 to the price field of a Product instance p?
- price.Product = 9.99;
- p.price = 9.99; Correct answer
- Product.price = 9.99;
- p(price, 9.99);
Explanation: P.price = 9.99; — instance name, dot, field name.
3 Complete the field declaration
class Product {
String name;
____ price;
}class Product {
String name;
double price;
}Explanation: The price field should be of type double.