Java – Access Modifiers

checkout sourcecode here

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.
package accessmodifierdemo.instancevariable;

class A {
    private int data = 40;

    private void msg() {
        System.out.println("Hello java");
    }
}

public class InnstanceVariable {
    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.
package accessmodifierdemo.defaultaccessmodifierdemo.pack;

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

//save by B.java

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.

package accessmodifierdemo.protectedaccessmodifierdemo.father;

public class A{
    protected void msg(){System.out.println("Hello");}
}
package accessmodifierdemo.protectedaccessmodifierdemo.child;


import accessmodifierdemo.protectedaccessmodifierdemo.father.A;

public class B extends A {
    public static void main(String args[]) {
        B obj = new B();
        obj.msg();
    }
}
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

package accessmodifierdemo.publicaccessmodiferdemo;

//save by A.java

public class A {
    public void msg() {
        System.out.println("Hello");
    }
}
package accessmodifierdemo.publicaccessmodiferdemo;


class B {
    public static void main(String args[]) {
        A obj = new A();
        obj.msg();
    }
}
Output:Hello

Understanding all java access modifiers

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

Access Modifier within class within package outside package by subclass only outside package
Private Y N N N
Default Y Y N N
Protected Y Y Y N
Public Y Y Y Y

Java access modifiers with method overriding

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

package accessmodifierdemo.finaldemo;

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.

Leave a Reply

Your email address will not be published. Required fields are marked *