Using _ (underscore) as Variable Name in Java

As we do know variables in java or rather in any language is introduced to write a code where it is suggested to give meaningful names to the variables as per their usage in code and especially in object-oriented languages are supposed to be used locally wherever it is possible instead of just using them globally. It is a very essential property of variables that is been checked is enterprising domain as it helps us achieve cleaner and minimalistic code. 

Case 1: Using underscore as a variable name in Java 8

Although it is supported in Java 8, a mandatory warning is issued if you use _ as an identifier, telling you that "use of '_' as an identifier might not be supported in releases after Java SE 8".

Example:

// Java Program to Illustrate Usage of Underscore
// As a Variable Name

// Main class
class GFG {

    // Main driver method
    public static void main(String args[])
    {
        // Declaring underscore as variable
        // in java 8 only
        int _ = 10;

        // Printing the value stored in it
        System.out.println(_);
    }
}

Output: 

10

With the advancement in the version of Java, Java 9 has made changes in features of the java language, and eliminating underscore from the legal name is a major change made by Oracle. The use of the variable name _ in any context is never encouraged. The latest versions of Java reserve this name as a keyword and/or give it special semantics. If you use the underscore character ("_") as an identifier, your source code can no longer be compiled. We will get a compile-time error.

Case 2: Using underscore as a variable name in Java 9

Example:

// Java program to illustrate Usage of Underscore
// As Variable Name in Java9

// Main class
class GFG {

    // Main driver method
    public static void main(String args[])
    {

        // Declaring underscore as variable
        // in java9 and onwards
        int _ = 10;

        // Printing the value as stored in underscore
        System.out.println(_);
    }
}

Output: In Java 9, underscore as variable name won't work altogether. Below source code can no longer be compiled.

Below are the following conclusions been drawn from the above examples as illustrated: 

1. Using underscore in a variable like first_name is still valid. But using _ alone as a variable name is no more valid.
2. Even if you are using earlier versions of Java, using only underscore as a variable name is just a plain bad style of programming and must be avoided.