Java variable or Java identifier

package com.javaexample4u.identifiers;

public class JavaIdentifiers {

      

/*     A name in a java Program is called an Identifier.Which can be used for representing classes,methods , variables and labels.

       Rules:

       1.Java Identifier is composed of a sequence of characters,

             Which each character may be a letter from a to z or A to Z or digit from 0 to 9 or currency symbol ($) or connecting symbol (_). i.e only a-z,A-Z,0-9,$ and _ 
If we use other character we will get compile time error saying illegal character.

       2.No identifier starts with the digit.

       3.There is no length limit for java identifier ,but SUN highly recommended up to 15 characters .

       4.Identifier in java are case sensitive.

       5.we are not allowed to use reserved words as identifier.

       6.All predefined java class and interface names ,you are allowed to use as identifiers.*/

       public static void main(String[] args) {

              String JAVA;//Correct

              String java;//Correct

              String        Java225; //Correct

              String java1$;//Correct

              String _java; //Correct

              String        javal_examples;//Correct

              String Runnable;//Correct and it is predefined interface name

              String Seriliazable;//Correct and it is predefined interface name

              String String ="Sekhar4j";//Correct and it is predefined java class String
              System.out.println(String);//it prints Sekhar4j if you comment below identifiers
                    

              String first-example;//Syntax error on token "first", = expected after this token

              //example cannot be resolved to a variable

              String 225java2; //Syntax error on token "225", delete this token

              String second1#;//   Syntax error on token "Invalid Character", delete this token

       }

}

/*

* OputPut after compilation:

* Exception in thread "main" java.lang.Error: Unresolved compilation problems:

       Syntax error on token "first", = expected after this token

       example cannot be resolved to a variable

       Syntax error on token "225", delete this token

       Syntax error on token "Invalid Character", delete this token

       at com.javaexample4u.identifiers.JavaIdentifiers.main(JavaIdentifiers.java:24)

)*/