Classes And Objects

Class Definition

Class is a blueprint in which characteristics (members) and behaviors (functions) are defined.

An example of class definition is:

class Person { public String name; int age; }

In the example:

• class is the keyword for class defining.
• Person - the name of the class.
• On lines 4 and 5 class members are declared - the properties that characterize the class.
• At line 3 we define the public parts of the class. public could be replaced with private or protected. The difference between public, private and protected is explained in other tutorials.

Object Creation

Object is an instance created from a class.

Using the defined class we can create objects and set properties.

class Person { public String name; int age; void introduceYourself() { System.out.print("I'm " + name + " and I'm " + age + "years old."); } } public class Main { public static void main(String[] args) { // create object Person personObject = new Person(); // set properties personObject.name = "John"; personObject.age = 20; personObject.introduceYourself(); } }

Output:

I'm John and I'm 20 years old.

Explanation:

• At lines 1 - 13 a class is defined. It's members are name and age defined at lines 4 and 5.
• The class also has a function introduceYourself that uses the members.
• At line 19 an object is created.
• At lines 22 and 23 values are set to the members.
• At lines 25 the function introduceYourself is called and a message is printed.