Tutorials References Exercises Videos Menu
Create Website Get Certified Upgrade

Java Tutorial

Java HOME Java Intro Java Get Started Java Syntax Java Output Java Comments Java Variables Java Data Types Java Type Casting Java Operators Java Strings Java Math Java Booleans Java If...Else Java Switch Java While Loop Java For Loop Java Break/Continue Java Arrays

Java Methods

Java Methods Java Method Parameters Java Method Overloading Java Scope Java Recursion

Java Classes

Java OOP Java Classes/Objects Java Class Attributes Java Class Methods Java Constructors Java Modifiers Java Encapsulation Java Packages / API Java Inheritance Java Polymorphism Java Inner Classes Java Abstraction Java Interface Java Enums Java User Input Java Date Java ArrayList Java LinkedList Java HashMap Java HashSet Java Iterator Java Wrapper Classes Java Exceptions Java RegEx Java Threads Java Lambda

Java File Handling

Java Files Java Create/Write Files Java Read Files Java Delete Files

Java How To

Add Two Numbers Count Words Reverse a String

Java Reference

Java Keywords Java String Methods Java Math Methods

Java Examples

Java Examples Java Compiler Java Exercises Java Quiz Java Certificate


Java Class Attributes


Java Class Attributes

In the previous chapter, we used the term "variable" for x in the example (as shown below). It is actually an attribute of the class. Or you could say that class attributes are variables within a class:

Example

Create a class called "Main" with two attributes: x and y:

public class Main {
  int x = 5;
  int y = 3;
}

Another term for class attributes is fields.


Accessing Attributes

You can access attributes by creating an object of the class, and by using the dot syntax (.):

The following example will create an object of the Main class, with the name myObj. We use the x attribute on the object to print its value:

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 »


Modify Attributes

You can also modify attribute values:

Example

Set the value of x to 40:

public class Main {
  int x;

  public static void main(String[] args) {
    Main myObj = new Main();
    myObj.x = 40;
    System.out.println(myObj.x);
  }
}

Try it Yourself »

Or override existing values:

Example

Change the value of x to 25:

public class Main {
  int x = 10;

  public static void main(String[] args) {
    Main myObj = new Main();
    myObj.x = 25; // x is now 25
    System.out.println(myObj.x);
  }
}

Try it Yourself »

If you don't want the ability to override existing values, declare the attribute as final:

Example

public class Main {
  final int x = 10;

  public static void main(String[] args) {
    Main myObj = new Main();
    myObj.x = 25; // will generate an error: cannot assign a value to a final variable
    System.out.println(myObj.x);
  }
}

Try it Yourself »

The final keyword is useful when you want a variable to always store the same value, like PI (3.14159...).

The final keyword is called a "modifier". You will learn more about these in the Java Modifiers Chapter.



Multiple Objects

If you create multiple objects of one class, you can change the attribute values in one object, without affecting the attribute values in the other:

Example

Change the value of x to 25 in myObj2, and leave x in myObj1 unchanged:

public class Main {
  int x = 5;

  public static void main(String[] args) {
    Main myObj1 = new Main();  // Object 1
    Main myObj2 = new Main();  // Object 2
    myObj2.x = 25;
    System.out.println(myObj1.x);  // Outputs 5
    System.out.println(myObj2.x);  // Outputs 25
  }
}

Try it Yourself »


Multiple Attributes

You can specify as many attributes as you want:

Example

public class Main {
  String fname = "John";
  String lname = "Doe";
  int age = 24;

  public static void main(String[] args) {
    Main myObj = new Main();
    System.out.println("Name: " + myObj.fname + " " + myObj.lname);
    System.out.println("Age: " + myObj.age);
  }
}

Try it Yourself »

The next chapter will teach you how to create class methods and how to access them with objects.