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Encapsulation in Java

Encapsulation in java is a process of wrapping code and data together into a single unit, for example capsule i.e. mixed of several medicines.

We can create a fully encapsulated class in java by making all the data members of the class private. Now we can use setter and getter methods to set and get the data in it.

The Java Bean class is the example of fully encapsulated class.

Advantage of Encapsulation in java

By providing only setter or getter method, you can make the class read-only or write-only.

It provides you the control over the data. Suppose you want to set the value of id i.e. greater than 100 only, you can write the logic inside the setter method.

Simple example of encapsulation in java

Let's see the simple example of encapsulation that has only one field with its setter and getter methods.

//save as Student.java package com.javatpoint; public class Student{ private String name; public String getName(){ return name; } public void setName(String name){ this.name=name } }


//save as Test.java package com.javatpoint; class Test{ public static void main(String[] args){ Student s=new Student(); s.setName("vijay"); System.out.println(s.getName()); } }


There are two types of modifiers in java: access modifiers and non-access modifiers.

The access modifiers in java specifies accessibility (scope) of a data member, method, constructor or class.

There are 4 types of java access modifiers:

  1. Private
  2. Default
  3. Protected
  4. Public

There are many non-access modifiers such as static, abstract, synchronized, native, volatile, transient etc. Here, we will learn access modifiers.

1) private access modifier

The private access modifier is accessible only within class.

Simple example of private access modifier

In this example, we have created two classes A and Simple. A class contains private data member and private method. We are accessing these private members from outside the class, so there is compile time error.

class A{ private int data=40; private void msg(){System.out.println("Hello java");} } public class Simple{ public static void main(String args[]){ A obj=new A(); System.out.println(obj.data);//Compile Time Error obj.msg();//Compile Time Error } }


Role of Private Constructor

If you make any class constructor private, you cannot create the instance of that class from outside the class. For example:

class A{ private A(){}//private constructor void msg(){System.out.println("Hello java");} } public class Simple{ public static void main(String args[]){ A obj=new A();//Compile Time Error } }


Note: A class cannot be private or protected except nested class.

2) default access modifier

If you don't use any modifier, it is treated as default bydefault. The default modifier is accessible only within package.

Example of default access modifier

In this example, we have created two packages pack and mypack. We are accessing the A class from outside its package, since A class is not public, so it cannot be accessed from outside the package.

//save by A.java package pack; class A{ void msg(){System.out.println("Hello");} }


//save by B.java package mypack; import pack.*; class B{ public static void main(String args[]){ A obj = new A();//Compile Time Error obj.msg();//Compile Time Error } }


In the above example, the scope of class A and its method msg() is default so it cannot be accessed from outside the package.

3) protected access modifier

The protected access modifier is accessible within package and outside the package but through inheritance only.

The protected access modifier can be applied on the data member, method and constructor. It can't be applied on the class.

Example of protected access modifier

In this example, we have created the two packages pack and mypack. The A class of pack package is public, so can be accessed from outside the package. But msg method of this package is declared as protected, so it can be accessed from outside the class only through inheritance.

//save by A.java package pack; public class A{ protected void msg(){System.out.println("Hello");} }


//save by B.java package mypack; import pack.*; class B{ public static void main(String args[]){ A obj = new A(); obj.msg(); } }


Understanding all java access modifiers

Let's understand the access modifiers by a simple table.

Java access modifiers with method overriding

If you are overriding any method, overridden method (i.e. declared in subclass) must not be more restrictive.

class A{ protected void msg(){System.out.println("Hello java");} } public class Simple extends A{ void msg(){System.out.println("Hello java");}//C.T.Error public static void main(String args[]){ Simple obj=new Simple(); obj.msg(); } }


The default modifier is more restrictive than protected. That is why there is compile time error.

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