updated java syntax to contain:

identifiers
modifiers
variables
enums
inheritance
interfaces

Author: newtonkiragu

SYNTAX.md

@@ -23,4 +23,55 @@ Example:
 Assume `MyFirstJavaProgram` is the class name, the file should be saved as `MyFirstJavaProgram.java`
 
 ### public static void main(String args[])
-Java processing starts from the `main()` method which is a mandatory part of every Java program
+Java processing starts from the `main()` method which is a mandatory part of every Java program
+
+### Java identifiers
+All java components require names. These names (classes, variables, methods) are called identifiers
+points to note:
+ - all identifiers should begin with letters (a-z, A-Z) or currency characters or underscores
+ -  key word cannot be used as an identifier
+ - Identifiers are case sensitive, (classes can only begin in caps, methods cannot begin in caps)
+
+### Java modifiers
+Used to make changes to classes. There are two categories:
+ - Access modifies - default, public, protected, private
+ - Non Access modifiers - final, abstract, strictfp
+
+### Java variables
+the following are java variables
+ - Local variables
+ - Class variables (Static variables)
+ - Instance variables (non static variables)
+
+### Java enums
+They restrict variables to have a few pre-defined values
+
+Example:
+
+if we consider an application for a fresh juice shop, it would be possible to restrict the glass size to small, medium, and large. This would make sure that it would not allow anyone to order any size other than small, medium, or large.
+
+```java
+class FreshJuice{
+    enum FreshJuiceSize {Small, Medium, Large}
+    FreshJuiceSize size;
+}
+
+public class FreshJuiceTest {
+
+    public static void main(String args[]) {
+        FreshJuice juice = new FreshJuice();
+        juice.size = FreshJuice.FreshJuiceSize.Medium;
+        System.out.println("size" + juice.size);
+    }
+}
+```
+
+### Inheritance
+In Java, classes can be derived from classes. Basically, if you need to create a new class and here is already a class that has some of the code you require, then it is possible to derive your new class from the already existing code.
+
+This concept allows you to reuse the fields and methods of the existing class without having to rewrite the code in a new class. In this scenario, the existing class is called the `superclass` and the derived class is called the `subclass`.
+
+### Interfaces
+In Java language, an interface can be defined as a contract between objects on how to communicate with each other. Interfaces play a vital role when it comes to the concept of inheritance.
+
+An interface defines the methods, a deriving class (subclass) should use. But the implementation of the methods is totally up to the subclass.