Attributes

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.

Exercise 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.

Show example 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);
    }
}

Test yourself

Match field types

int

Integer
double

Decimal
String

Text
boolean

Logical
How do you assign 9.99 to the price field of a Product instance p?
- price.Product = 9.99;
- p.price = 9.99;
- Product.price = 9.99;
- p(price, 9.99);
Show answer

p.price = 9.99; — P.price = 9.99; — instance name, dot, field name.

Complete the field declaration

class Product {
    String name;
    ____ price;
}

Show answer

class Product {
    String name;
    double price;
}

Next lesson: Methods

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