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Java Extended
Java Extended
What is Class?
Class
A class is a fundamental concept in OOP programming. It refers to a template for creating objects. A class consists of fields (data) and methods (behavior). Let's consider the class Dog
, where the fields (data) would be information about the dog's name
and age
, and the method (behavior) would make the dog introduce itself and say its name:
Dog
class Dog { String name; int age; void introduce() { System.out.println("Woof, woof (which means 'My name is " + name + "!')."); } }
Let's consider what constitutes data (fields) and what represents behavior (methods):
As we can see from the diagram, we have fields that are not initialized within the class itself, as well as a method that is not yet called anywhere. Let's create an object of the Dog
class in the main class and initialize its fields:
Main
public class Main { public static void main(String[] args) { Dog dog = new Dog(); dog.name = "Brian"; dog.age = 13; } }
We created an object of the Dog
class and named it dog
.
The syntax for creating an object of a class is:
ClassName objectName = new ClassName();
We also initialized the properties of the object by assigning values to the fields.
Our dog's name is Brian
, and the age is 13
.
The syntax for initializing the fields of an object is:
objectName.fieldName = value;
So now we have an object of the Dog
class with initialized fields.
Let's now invoke a method from our Dog
class:
Main
package com.example; class Dog { String name; int age; void introduce() { System.out.println("Woof, woof (which means 'My name is " + name + "!')."); } } public class Main { public static void main(String[] args) { Dog dog = new Dog(); dog.name = "Brian"; dog.age = 13; dog.introduce(); } }
We successfully invoked a method from the Dog
class by using that method on the Dog
object. You may have noticed the same syntax when we called methods from the String
class earlier.
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