Access Modifier In Java
Access modifiers:
Access modifiers are keywords used for defining accessibility of classes, methods and data members.
Types of access modifier.
- 1. Private.
- 2. Default
- 3. Protected
- 4. Public
Private:
Data members, methods and constructors that are declared with private access modifier can be accessed into that class only.
Example:
PrivateAccessModifier.java
/**
* This program is used to show that private members
* of a class can be accessed in that class only
* @author javatutorialpoint
*/
class Student {
//private members of the class
private int rollNo = 5;
private void showRollNo(){
//rollNo which a private data member is
//accessible in that class.
System.out.println("RollNo = " + rollNo);
}
}
public class PrivateAccessModifier {
public static void main(String args[]){
//creating Student class object
Student obj = new Student();
//compile time error because private members
//of a class can be accessed in that class only.
System.out.println(obj.rollNo);
obj.showRollNo();
}
}
|
Output:
Exception in thread "main" java.lang.Error:
Unresolved compilation problems:
The field Student.rollNo is not visible
The method showRollNo() from the type Student is not visible
at com.javawithease.business.PrivateAccessModifier.main
(PrivateAccessModifier.java:24)
|
Note: A class can have a private constructor but we cannot create an instance of that class from outside the class.
PrivateConstructor.java
/**
* This program is used to show that we cannot create an instance
* of that class from outside the class if constructor is private.
* @author javatutorialpoint
*/
class Student {
//private constructor of the class
private Student(){
}
public void show(){
System.out.println("Hello javawithease.com");
}
}
public class PrivateConstructor {
public static void main(String args[]){
//compile time error in creating Student class object
//because of private constructor.
Student obj = new Student();
}
}
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Output:
Exception in thread "main" java.lang.Error:
Unresolved compilation problem:
The constructor Student() is not visible
at com.javawithease.business.PrivateConstructor.main
(PrivateConstructor.java:22)
|
Note: Classes and interfaces can’t be private except nested classes.
Default:
Classes, data members, methods and constructors that are not declared with any access modifier are treated as default. They can be accessed into all classes within the same package only.
Example 1:
DefaultAccessModifier1.java
/**
* This program is used to show that members of the class
* of a class can be accessed in the package level only.
* @author javatutorialpoint
*/
class Student {
//private members of the class
int rollNo = 5;
void showRollNo(){
System.out.println("RollNo = " + rollNo);
}
}
public class DefaultAccessModifier1 {
public static void main(String args[]){
//creating Student class object
Student obj = new Student();
//No compile time error because members of the class
//of a class can be accessed in that package but can't be
//accessed outside the package.
System.out.println(obj.rollNo);
obj.showRollNo();
}
}
|
Output:
Example 2:
Display.java
package com.javawithease.display;
/**
* This class is used to print a line.
* @author javatutorialpoint
*/
class Display {
void display(){
System.out.println("Hello javawithease.com");
}
}
|
Test.java
package com.javawithease.test;
import com.javawithease.display.*;
/**
* This program is used to show that default members of the class
* are not accessible from outside the package.
* @author javatutorialpoint
*/
public class Test {
public static void main(String args[]){
//compile time error because default members of the class
//are not accessible from outside the package.
Display obj = new Display();
obj.display();
}
}
|
Output:
Exception in thread "main" java.lang.Error:
Unresolved compilation problems:
The type Display is not visible
The type Display is not visible
The type Display is not visible
at com.javawithease.test.Test.main(Test.java:13)
|
Protected:
Data members, methods and constructors that are declared with protected access modifier can be accessed into all classes within the same package and only in subclasses outside the package.
Example 1:
Display.java
package com.javawithease.display;
/**
* This class is used to print a line.
* @author javatutorialpoint
*/
public class Display {
protected void display(){
System.out.println("Hello javawithease.com");
}
}
|
Test.java
package com.javawithease.display;
package com.javawithease.test;
import com.javawithease.display.*;
/**
* This program is used to show that protected members of the
* class are accessible from outside the package in subclasses.
* @author javatutorialpoint
*/
public class Test extends Display{
public static void main(String args[]){
Test obj = new Test();
//No compile time error because protected members
//of the class are accessible from outside the
//package in subclasses.
obj.display();
}
}
|
Output:
Example 2:
Display.java
package com.javawithease.display;
/**
* This class is used to print a line.
* @author javatutorialpoint
*/
public class Display {
protected void display(){
System.out.println("Hello javawithease.com");
}
}
|
Test.java
package com.javawithease.test;
import com.javawithease.display.*;
/**
* This program is used to show that protected members of the class
* are not accessible from outside the package in non-subclasses.
* @author javatutorialpoint
*/
public class Test {
public static void main(String args[]){
Display obj = new Display();
//compile time error because protected members
//of the class are not accessible from outside
//the package in non-subclasses.
obj.display();
}
}
|
Output:
Exception in thread "main" java.lang.Error:
Unresolved compilation problem:
The method display() from the type Display is not visible
at com.javawithease.test.Test.main(Test.java:15)
|
Note: Classes and interfaces can’t be protected except nested classes.
Public:
Classes, data members, methods and constructors that are declared with public access modifier can be accessed everywhere.
Example:
Display.java
package com.javawithease.display;
/**
* This class is used to print a line.
* @author javatutorialpoint
*/
public class Display {
public void display(){
System.out.println("Hello javawithease.com");
}
}
|
Test.java
package com.javawithease.test;
import com.javawithease.display.*;
/**
* This program is used to show that public members of the class
* are accessible everywhere.
* @author javatutorialpoint
*/
public class Test {
public static void main(String args[]){
Display obj = new Display();
//public members of the class accessible everywhere.
obj.display();
}
}
|
Output:
