>> Access Modifiers

Access Modifiers in Java

Access Modifiers determines the level of access or visibility of data or method or constructor. There are four types of access modifiers in Java :

Public

Private

Protected

Default

Public

They have highest level of accessibility or visibility.  The keyword is "public". They are accessible from everywhere in the java project.

Private

The keyword is "private". They are accessible within the class only in which they are declared or created.

Class1 having public and private data:

public class Test1{

      

       private Test1() { 

              System.out.println("This is private constructor test.");

       }

      

       private int x = 10;

      

       private void method1() {         

              System.out.println("This is private method test.");

       }

      

       public Test1(String test) {

              System.out.println("This is public constructor test.");

       }

      

       public int xx = 20;

      

       public void methodA() {          

              System.out.println("This is public method test.");

       }

}

Class2 : trying to use data from Class1

public class Test2 {

       public static void main(String[] args) {       

              Test1 a = new Test1(); //you get compilation error when you try to create object of private constructor.

              Test1 b = new Test1("ok"); //you do not get compilation error because this is public.

             

              b.method1(); //getting compilation error

              b.methodA(); //Not getting compilation error

             

              System.out.println("private variable " +b.x);//getting compilation error

              System.out.println("public variable " +b.xx);//Not getting compilation error  

       }

}

Note: When you comment out the statements showing error in class2, and run, you get below output:

This is public constructor test.

This is public method test.

public variable 20

Protected

They use the keyword "protected". They are accessible within the package and if the class is extended(inherited) by another class, outside the package, then they are accessible in the child class as well. Through inheritance, protected data are accessible outside the package.

While running inside same package "packageA":

Class1:

package packageA;

public class Test1{

      

       protected Test1() { 

              System.out.println("This is protected constructor test.");

       }

      

       protected int x = 10;

      

       protected void method1() {       

              System.out.println("This is protected method test.");

       }

}

Class2 inside same package:

package packageA;

public class Test2 {

       public static void main(String[] args) {       

              Test1 a = new Test1();

              a.method1();

             

              System.out.println("Protected variable " +a.x);

      

       }

}

Output:

This is protected constructor test.

This is protected method test.

Protected variable 10

Getting compilation error when tried to use the data in different/outside package "packageB":

package packageB;

import packageA.Test1;

public class Test3 {

       public static void main(String[] args) {       

              Test1 a = new Test1(); // getting compilation error

              a.method1(); // getting compilation error

             

              System.out.println("Protected variable " +a.x); // getting compilation error

      

       }

}

Now, let's apply inheritance and use the data in the outside package "packageB".

Now, we should not get compilation error :

package packageB;

import packageA.Test1;

public class Test3 extends Test1{

       public static void main(String[] args) {       

              Test3 a = new Test3();

              a.method1();

             

              System.out.println("Protected variable " +a.x);

      

       }

}

Output:

This is protected constructor test.

This is protected method test.

Protected variable 10

Default

When you do not mention the access modifier in constructor, method or variable, then it is default access modifier. The data is accessible within the package only where the data is created.

While running inside same package "packageA":

Class1:

package packageA;

public class Test1{

      

       Test1() { 

              System.out.println("This is default constructor test.");

       }

      

       int x = 10;

      

       void method1() {          

              System.out.println("This is default method test.");

       }

}

Class2 inside the same package "packageA".

package packageA;

public class Test2 {

       public static void main(String[] args) {       

              Test1 a = new Test1();

              a.method1();

             

              System.out.println("Default variable " +a.x);

      

       }

}

Output:

This is default constructor test.

This is default method test.

Default variable 10

Getting compilation error when tried to use the data in different  package "packageB":

package packageB;

import packageA.Test1;

public class Test3 {

       public static void main(String[] args) {       

              Test1 a = new Test1(); //getting compilation error

              a.method1(); //getting compilation error

             

              System.out.println("Protected variable " +a.x); //getting compilation error

      

       }

}

Let's apply inheritance and try to use the data in different package "packageB", still we should get compilation error.

package packageB;

import packageA.Test1;

public class Test3 extends Test1 { //getting compilation error

       public static void main(String[] args) {       

              Test3 a = new Test3();

              a.method1(); //getting compilation error

             

              System.out.println("Protected variable " +a.x); //getting compilation error

      

       }

}