How to check if a variable is defined in Java

In this post, we will be discussing a variable, how it is declared and how to check its presence in Java. Every program made out of a language contains data that is executed and implemented in the way it is coded. Without data, there will be nothing for the computer to understand and run the login on. Let us first understand what a variable is:

Variable in Java

A variable in simple words is a vessel that holds something which is used in the logic of an executable program. Java is a language that cares about the type of data. Variables contain data in them and these variables should have a type and a name given to the type.
Example: int ant; – here ‘int‘ is the type of data and ‘ant’ is the name given to the declared integer.

Now let’s see how to declare and check a variable:
Variables can be declared in three ways:

1. As object state (instance variables)
2. Within the method (local variables)
3. As return types

If a variable is not properly declared, that is- if the type of the variable or the format of the name given to the variable is incorrect then the program will not give the expected output and it won’t be executed as it has problems interpreting the data input.

Check if a variable exists or not in a program in Java

To check if a variable is declared in Java or not, in a simple way an if conditional can be used in the following way:

if (variablename != NULL)
{//does something for example:
System.out.println("Variable declared");
}
else
{//does something else for example:
System.out.println("Variable not declared");
}

In the above code, in the if conditional if the declared variable is not null then it will print “Variable declared” and if it is not declared the screen output will print “Variable not declared”. This is a simple way to check if a variable is declared in a Java program.