How do I write variable names in Java?

While choosing an identifier to declare a variable in Java you need to keep the following points in mind.

• The name of the variable should begin with either alphabet or, an underscore (_) or, a dollar ($) sign.
• The identifiers used for variables must not be keywords.
• No spaces or special characters are allowed in the variable names of Java.
• Variable names may contain 0 to 9 numbers (if not at the beginning).
• Variable names are case sensitive i.e. MY_NUM is different from my_num.
• If you use two words in a identifier then the you should follow camel case first letter of first word should be in lowercase and the first letters of later words should be in lower case ex: myNum.

Example

Following example shows various possible identifiers used to declare a variable in Java.

Live Demo

public class VariableTest {
   public static void main(String args[]) {
      // Declaring a variable named num
      int num = 1;
      int _num = 10;
      int $num = 100;
      int num123 = 1000;
      int NUM = 10000;     
      int myNum = 100000;
      // Printing the value of the variable num
      System.out.println("value if the variable num: "+num);
      System.out.println("value if the variable _num: "+_num);
      System.out.println("value if the variable $num: "+$num);
      System.out.println("value if the variable num123: "+num123);
      System.out.println("value if the variable NUM: "+NUM);
      System.out.println("value if the variable myNum: "+ myNum);
   }
}

Output

value if the variable num: 1
value if the variable _num: 10
value if the variable $num: 100
value if the variable num123: 1000
value if the variable NUM: 10000
value if the variable myNum: 100000