QN036. Write a class which demonstrates the use of public, private, and protected access specifier.

---

1. Objective

To demonstrates the use of public, private and protected access specifier.

2. Theory

In Java, the term access modifiers refers to the keywords which are used to control accessibility to classess, interfaces, fields, constructors and methods. That means we can determine what can access our code.
In java, we have four types of access modifiers.
i) default ii) private iii) protected iv) public

i. default

When we do not mention any access modifier, it is called default access modifier. The scope of this modifier is limited to the package only. It we have a default class, method or data member in a class, it would not be visible in the class of another package.

ii. private

The scope of private modifier is limited to the class only. Private data members and methods are only accessible with in class. Class and interface cannot be declared as private. If a class has private constructor then we cannot create the object of that class from outside of the class.

iii. protected

Protected data member and methods are only accessible by the classes of the same package and the subclasses present in any package. We can also say that the protected access modifider is similar to default access modifier with one exception that it has visibility in sub classes.
Classes cannot be declared as protected. This access modifier is generally used in a parent child relationship.

iv. public

The members, methods and classes that are declared public can be access from anywhere. This modifier doesn't put any restriction on the access.

3. Source Code

//3.1 default access modifier
//Addition.java

package myPackage;
public class Addition{
int addTwoNumbers(int x, int y){
return x+y;
}
}

//TestDefault.java

package hisPackage;
import myPackage.*;
public class TestDefault {
public static void main(String[] args){
Addition addObj = new Addition();
addObj.addTwoNumbers(20,30);
}
}

//3.2 private access modifier
//privateABC.java

class privateABC{
private int num = 100;
private int square(int a){
return a*a;
}
}

//TestPrivate.java

public class TestPrivate{
public static void main(String[] args){
privateABC obj = new privateABT();
System.out.println(obj.num);
System.out.println(obj.square(10));
}
}

//3.3 protected access modifier
//Addition.java

package myPackage;
public class Addition{
protected int addTwoNumbers(int a, int b){ return a+b;
}
}

//TestProtected.java

package hisPackage;
import myPackage.*;
class TestProtected extends Addition{
public static void main(String[] args){
TestProtected obj = new TestProtected();
System.out.println(obj.addTwoNumber(12,15));
}
}

//3.4 public access modifier
//Addition.java

package abcPackage;
public class Addition {
public int addTwoNumbers(int a, int b){
return a+b;
}
}

//Test.java

package xyzPackage;
import abcPackage;
class Test{
public static void main(String[] args){
Addition obj = new Addition();
System.out.println(obj.addTwoNumbers(10,20))
}
}


4. Output

Output: 3.1 default access modifier
Exception in thread "main" java.lang.Error: unresolved compilation problem: The method addTwoNumbers(int,int) from the type Addition is not visible at hisPackage. TestDefault.main(TestDefault.java:7)

Output: 3.2 private access modifier
compile-time error

Output: 3.3 protected access modifier
27

Output 3.4 public access modifier
30

5. Conclusion

In this way, I would like to conclude that, we can use different kind of access modifier according to our requirements