Interface.java

/*
Copyright (c) 2017-2018 Navjot Singh Virk (Website: https://navsingh.org.uk),
(Project Git: https://github.com/virksaabnavjot/jcode)

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*/

/*
*Interface.java
*Purpose: To learn to use interface in java and understand the meaning of it.
*Date: 13/August/2017 | Sunday | 00:22 am (Dublin,Ireland)
*/

/*Explanation: What is Interface ? Why use it? How to make use of it ? How to implement it?
http://tutorials.jenkov.com/java/interfaces.html
(Hindi) https://www.youtube.com/watch?v=P1qhuqY2HxE&t=836s

Interface (meaning - interact with )

1-Interface just specify the method declaration (implicitly public and abstract)
Example: public void greetings();

2-We dont really have to write the "public" keyword as all the methods of
an interface are public by default.
Example: void greetings(); is also correct.

3-Interface can only contain fields which are (implicitly public static final)
Example: public static final String name = "Navjot";

or

String name = "Navjot"; is also correct and its (public static and final by default
so, we dont really need to write these).

4- An Interface like an abstract class cannot be instantiated (meaning we cant create
objects of an interface).

5- An Interface do not have a constructor (as we cant create object what do we need
constructor for?).

6- If a class that implements an interface doesn't implement/define all the methods
of that interface, then that class must be declared as an abstract class and method
declerations must be provided by the subclasses that extent the abstract class.

*/

public interface Interface{

  /*Variables - Syntax: dataType variableName = value;
  (both the variables below are public, static and final by default either
  we write public static final or not)
  */
  public static final String firstName = "Navjot";
  String lastName = "Singh";


  /*Methods - Syntax: returnType methodName(parameters);
  methods are abstract and public by default no matter we add public or not its
  the same thing.
  */
  public void greetings();
  int guessAge(int age);

}