Access
Modifiers in java
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:
- private
- default
- protected
- 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.
|
1.
class A{
2.
private int data=40;
3.
private void msg(){System.out.println("Hello java");}
4.
}
5.
6.
public class Simple{
7.
public static void main(String args[]){
8.
A obj=new A();
9.
System.out.println(obj.data);//Compile Time Error
10.
obj.msg();//Compile Time Error
11.
}
12. }
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:
|
1.
class A{
2.
private A(){}//private constructor
3.
void msg(){System.out.println("Hello java");}
4.
}
5.
public class Simple{
6.
public static void main(String args[]){
7.
A obj=new A();//Compile Time Error
8.
}
9. }
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.
|
1.
//save by A.java
2.
package pack;
3.
class A{
4.
void msg(){System.out.println("Hello");}
5. }
1.
//save by B.java
2.
package mypack;
3.
import pack.*;
4.
class B{
5.
public static void main(String args[]){
6.
A obj = new A();//Compile Time Error
7.
obj.msg();//Compile Time Error
8.
}
9. }
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
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.
1.
class A{
2.
protected void msg(){System.out.println("Hello java");}
3.
}
4.
5.
public class Simple extends A{
6.
void msg(){System.out.println("Hello java");}//C.T.Error
7.
public static void main(String args[]){
8.
Simple obj=new Simple();
9.
obj.msg();
10.
}
11. }
|
The default modifier is more restrictive than protected. That is
why there is compile time error.
|
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