java classes

Java Classes/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 real life, a car is an object. The car has attributes, such as weight and color, and

methods, such as drive and brake.

A Class is like an object constructor, or a "blueprint" for creating objects.

Create a Class

To create a class, use the keyword class:

Main.java

Create a class named "Main" with a

variable x:

public class Main {

  int x = 5;

}

Remember from the Java Syntax chapter that a class should always start with an uppercase first letter, and that the name of the java file should match the class name.

Create an Object

In Java, an object is created from a class. We have already created the class named MyClass,

so now we can use this to create objects.

To create an object of MyClass,

specify the class name, followed by the object name, and use the keyword new:

Example

Create an object called "myObj" and print the value of x:

public class Main {

  int x = 5;



  public static void main(String[] args) {

    Main myObj = new Main();

    System.out.println(myObj.x);

  }

}

Try it Yourself »

Multiple Objects

You can create multiple objects of one class:

Example

Create two objects of Main:

public class Main {

  int x = 5;



  public static void main(String[] args) {

    Main myObj1 = new Main();  // Object 1

    Main myObj2 = new Main();  // Object 2

    System.out.println(myObj1.x);

    System.out.println(myObj2.x);

  }

}

Try it Yourself »

Using Multiple Classes

You can also create an object of a class and access it in another class. This

is often used for better organization of classes (one class has all the

attributes and methods, while the other class holds the main() method (code to

be executed)).

Remember that the name of the java file should match the class name. In this

example, we have created two files in the same directory/folder:

Main.java

Second.java

Main.java

public class Main {

  int x = 5;

}

Second.java

class Second {

  public static void main(String[] args) {

    Main myObj = new Main();

    System.out.println(myObj.x);

  }

}

When both files have been compiled:

Run the Second.java file:

And the output will be:

5

You will learn much more about classes and objects in the next chapters.

Test Yourself With Exercises

Exercise:

Create an object of MyClass called myObj.

Start the Exercise