JAVA Access Modifiers

Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors.

The four access levels are:

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.

Example :- 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.

1. //save by A.java  
2. package pack;  
3. public class A{  
4. protected void msg(){System.out.println("Hello");}  
5. }  

1. //save by B.java  
2. package mypack;  
3. import pack.*;  
4.   
5. class B extends A{  
6.   public static void main(String args[]){  
7.    B obj = new B();  
8.    obj.msg();  
9.   }  
10. }  

Output:Hello

---

4) public access modifier

The public access modifier is accessible everywhere. It has the widest scope among all other modifiers.

Example of public access modifier

1. //save by A.java  
2.   
3. package pack;  
4. public class A{  
5. public void msg(){System.out.println("Hello");}  
6. }  

1. //save by B.java  
2.   
3. package mypack;  
4. import pack.*;  
5.   
6. class B{  
7.   public static void main(String args[]){  
8.    A obj = new A();  
9.    obj.msg();  
10.   }  
11. }  

Output:Hello

Summary :-

Modifier    | Class | Package | Subclass | World

public      |  Y    |    Y    |    Y     |   Y

protected   |  Y    |    Y    |    Y     |   N

no modifier |  Y    |    Y    |    N     |   N

private     |  Y    |    N    |    N     |   N