Tutorials References Exercises Videos Pro NEW Menu
Paid Courses Website NEW

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

Java Reference

Java Keywords Java String Methods Java Math Methods

Java Examples

Java Examples Java Compiler Java Exercises Java Quiz Java Certificate


Java Encapsulation


Encapsulation

The meaning of Encapsulation, is to make sure that "sensitive" data is hidden from users. To achieve this, you must:

  • declare class variables/attributes as private
  • provide public get and set methods to access and update the value of a private variable

Get and Set

You learned from the previous chapter that private variables can only be accessed within the same class (an outside class has no access to it). However, it is possible to access them if we provide public get and set methods.

The get method returns the variable value, and the set method sets the value.

Syntax for both is that they start with either get or set, followed by the name of the variable, with the first letter in upper case:

Example

public class Person {
  private String name; // private = restricted access

  // Getter
  public String getName() {
    return name;
  }

  // Setter
  public void setName(String newName) {
    this.name = newName;
  }
}

Example explained

The get method returns the value of the variable name.

The set method takes a parameter (newName) and assigns it to the name variable. The this keyword is used to refer to the current object.

However, as the name variable is declared as private, we cannot access it from outside this class:

Example

public class Main {
  public static void main(String[] args) {
    Person myObj = new Person();
    myObj.name = "John";  // error
    System.out.println(myObj.name); // error 
  }
}

Run Example »

If the variable was declared as public, we would expect the following output:

John

However, as we try to access a private variable, we get an error:

MyClass.java:4: error: name has private access in Person
    myObj.name = "John";
         ^
MyClass.java:5: error: name has private access in Person
    System.out.println(myObj.name);
                  ^
2 errors

Instead, we use the getName() and setName() methods to access and update the variable:

Example

public class Main {
  public static void main(String[] args) {
    Person myObj = new Person();
    myObj.setName("John"); // Set the value of the name variable to "John"
    System.out.println(myObj.getName());
  }
}

// Outputs "John"

Try it Yourself »


Why Encapsulation?

  • Better control of class attributes and methods
  • Class attributes can be made read-only (if you only use the get method), or write-only (if you only use the set method)
  • Flexible: the programmer can change one part of the code without affecting other parts
  • Increased security of data