Core Java -Modifier

Types of Java Modifier

Modifiers arekeywords that you add to those definitions to change their meanings. The Java language has a wide variety of modifiers, including the following:

1. Access Modifiers

Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are:
  • default : Visible to the package. No modifiers are needed.
  • private : Visible to the class only.
  • public : Visible to the world.
  • protected : Visible to the package and all subclasses.

    • Default Access Modifier - No keyword:
    Default access modifier means we do not explicitly declare an access modifier for a class, field, method, etc. A variable or method declared without any access control modifier is available to any other class in the same package. The fields in an interface are implicitly public static final and the methods in an interface are by default public Eg: 
        String version ="1.5.1";
    boolean processOrder(){
    return true;
    }
    Private Access Modifier - private:
    Methods, Variables and Constructors that are declared private can only be accessed within the declared class itself. Private access modifier is the most restrictive access level. Class and interfaces cannot be private. Variables that are declared private can be accessed outside the class if public getter methods are present in the class. Using the private modifier is the main way that an object encapsulates itself and hide data from the outside world.
    Eg: 
        public class Logger{
      private String format;
      public String getFormat(){
      return this.format;
      }
        public void setFormat(String format){
      this.format = format;
      }
    }
    Public Access Modifier - public:
    A class, method, constructor, interface etc declared public can be accessed from any other class. Therefore fields, methods, blocks declared inside a public class can be accessed from any class belonging to the Java Universe. However if the public class we are trying to access is in a different package, then the public class still need to be imported. Because of class inheritance, all public methods and variables of a class are inherited by its subclasses.
    Eg: 
        public static void main(String[] arguments){
        // ...
    }
    Protected Access Modifier - protected:
    Variables, methods and constructors which are declared protected in a superclass can be accessed only by the subclasses in other package or any class within the package of the protected members' class.
    The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected, however methods and fields in a interface cannot be declared protected. Protected access gives the subclass a chance to use the helper method or variable, while preventing a nonrelated class from trying to use it.
    Eg: 
        class AudioPlayer{
      protected boolean openSpeaker(Speaker sp){
      // implementation details
      }
      }
      class StreamingAudioPlayer{
      boolean openSpeaker(Speaker sp){
      // implementation details
      }
    }

    2. Non Access Modifiers

    To use a modifier, you include its keyword in the definition of a class, method, or variable. The modifier precedes the rest of the statement, as in the following examples (Italic ones):
    Eg: 
        public class className {
      private boolean myFlag;
      static final double weeks =9.5;
      protected static final int BOXWIDTH =42;
      public static void main(String[] arguments){
      // body of method
      }
    }
    Access Control Modifiers:
    Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are:
  • default : Visible to the package. No modifiers are needed.
  • private : Visible to the class only.
  • public : Visible to the world.
  • protected : Visible to the package and all subclasses.

    • Non Access Modifiers:
    Java provides a number of non-access modifiers to achieve many other functionality.
  • The static modifier for creating class methods and variables
  • The final modifier for finalizing the implementations of classes, methods, and variables.
  • The abstract modifier for creating abstract classes and methods.
  • The synchronized and volatile modifiers, which are used for threads.
    • To use a modifier, you include its keyword in the definition of a class, method, or variable. The modifier precedes the rest of the statement, as in the following examples (Italic ones):
    Eg: 
        public class className {
      private boolean myFlag;
      static final double weeks =9.5;
      protected static final int BOXWIDTH =42;
      public static void main(String[] arguments){
      //...statement
      }
    }


    (Core Java - Operators)