Java Classes and Objects

Java is an object-oriented programming language.

Everything in Java is associated with classes and objects, along with its attributes and methods.

For Example, in a real life, a car is an object. The car has attributes, such as color and model, and methods, such as braking system and drive.

A class is like an object constructor, or a “blueprint” for creating objects.

 

Create a class

To create a class, we use the keyword class:

Example

public class ClassExample {
       String text = "Hello World";
}

Note: The class name should always start with the upper case as per the Java Syntax rules and the name of the file should always match with the class name.

 

Create an object

In Java, an object is created from a class. To create an object, specify the class name followed by object name, and use the keyword new:

Example

public class ClassExample {
       String text = "Hello World";
      
       public static void main (String args[]){
              ClassExample myObj = new ClassExample();
              System.out.println(myObj.text);
       }
}

Output

Hello World

 

Creating Multiple Objects

Multiple Objects can be created of one class.

Example

Here we create two objects  of ClassExample:

public class ClassExample {
       String text = "Hello World";

       public static void main (String args[]){
              ClassExample myObj1 = new ClassExample();
              ClassExample myObj2 = new ClassExample();
              System.out.println(myObj1.text);
              System.out.println(myObj2.text);
       }
}

 

Output

Hello World
Hello World

 

Using Multiple Classes

An object for a class is created and can be accessed it in another class. Through this, we can better organize the classes (once class can hold all the attributes and methods, while the other class holds the main() method (from where the code execution starts).

There can be only one public class in the Java file but there can be as many class files in the Java file.

In this example, we create two files under the same directory/folder.

·         MyClass.java

·         MainClass.java

 

MyClass.java

public class MyClass {
       String text = "Hello World!";
}

MainClass.java

public class MainClass {
       public static void main (String args[]){
              MyClass myObj = new MyClass();
              System.out.println(myObj.text);
       }
}

Output

We compile both the files separately and run the MainClass.java file.

Hello World!