8. Java - Java Modifiers

What is Java Modifier?

Java Modifier is a keyword used for changing the behavior of variable or class in term of its usage.
Java Modifier is categorized in two parts:-

1. Access Modifier
2. Non Access Modifier 

How can we use a modifier?

Simple usage of modifier:

modifier variableName;

where modifier is a keyword i.e. public, private, protected, static, final etc...

What is Java Access Modifier?

Java Access Modifier is like a security key which gives different access to classes, variables, methods or constructor .  In simple word, it controls the access level and it use for security reason.

The four Java Access Modifier are:

1. default :-> It gives access to package (no need to write it).
2. public :-> Give access to the world.
3. private :-> Give access to the class only.
4. protected :-> Give access to package and all sub classes.

Example:

//This class can be used by the world.

public class Test{

   private int myInt; //this variable only access by class Test.

   public String myString; //this variable access by everyone.

   protected int count; //this variable can access in class and sub class.

   private void myMethod(){

    

   }

}

What is Java Non Access Modifier?

Java Non Access Modifier provide various functionality and they are as follows:

1. static :-> this modifier allows direct access to method and variable without creating an object for its class.
2. final :-> this modifier affect class, method and variable too in following ways:
1. A class cannot be subclassed by using final modifier.
2. A method cannot be override with its sub class.
3. A variable cannot change its value one initialized.
3. abstract :-> it use for creating abstract class or method. It means if a class is abstract then it can't be use as a object. It only work as a parent class and it's subclass must have to complete its abstract methods.
   Example:
   
   abstract class A{
       ......
       ......
       public abstract void myMethod();
   }
   
   class B extends A{
       ......
       ......
       @Override    public void myMethod(){
          .....
          .....
       }
   }
4. synchronized :->this modifier used in thread, so we can discuss in Thread tutorial.
5. volatile :-> this modifier also used in thread.

Some important information: 

1. We can use  1 Access Modifier with  1 or more Non-Access Modifier for same variable/class/method.
2. We cannot use abstract and final same time.
3. We cannot use private with abstract.

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