The var keyword in Java 10 introduces a form of local type inference, allowing developers to declare variables without explicitly specifying their data types. Prior to Java 10, every variable declaration required a clear and explicit type annotation. However, it often resulted in verbose code, especially when dealing with complex or nested types. First thing you can notice is that with var we don’t need to explicitly declare the type, it will be inferred by the compiler by looking at what was passed as the initializer in the declaration.

In the above example, name is inferred to be of type String, version is int, and list is ArrayList. Note that var can only be used to declare local variables inside methods, and in for-loop and try-with-resources statements. Java’s var keyword allows developers to declare local variables without specifying a data type such as int, long, String or char.

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A new language feature introduced in the 2018 JDK 10 release, the Java var keyword performs type inference. The var reserved type name (not a Java keyword) was introduced in Java 10. Type inference is used in var keyword in which it detects automatically the datatype of a variable based on the surrounding context. The below examples explain where var is used and also where you can’t use it. In our IDE we can still see the type of var variables but not in Git repositories.

This gave me a thought that I should write a blog about this which will help the community who are still unaware of the var keyword in Java. Note that on the two previous examples, you have used var to declare a variable in a for statement and in a try-with-resources statement. Note that in all of these cases, the variable names are var keyword in java descriptive and the initializer is clear.

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1. At initialization, a type is going to be inferred by the compiler.
2. Type inference is used in var keyword in which it detects automatically the datatype of a variable based on the surrounding context.
3. This, in turn, enhances the readability of the codebase, making it easier to focus on the essential logic and structure of the program.
4. Instead, it was more of a friendly change that makes Java methods easier to write, easier to read and more approachable for programmers who are new to the language.
5. If you enter text it will be interpreted as a string, etc. var can even hold various objects and will behave properly.

This can reduce readability for sure, BUT this is even more an opportunity to improve our codebase. As you can see in the following var examples, the left-hand side of the assignment does not reference a Java types such as long, double or ArrayList. Instead, it uses the Java var keyword, which allows the JDK’s compiler to pick the appropriate type instead.

The var keyword allows a variable to be initialized without having to declare its type. The type of the variable depends on the type of the data that is being assigned to it. Var is a reserved type name, not a keyword, which means that existing code that uses var as a variable, method, or package name is not affected.

When not to use var in Java

With var, changes to the variable’s type do not necessitate modifying the declaration explicitly, reducing the chances of introducing errors. Var was introduced with the purpose of serve the cleaner/better readability and NOT to amend the Type System of the Java language. The above code is using var, it makes it easy to see and understand the variables. But to work, we need to give good descriptive names to our variables, and that is a good practice for all languages. In these examples, var replaces the explicit type declaration (String, int, ArrayList), making the code shorter and, in many cases, easier to read. Inferred type of the variable will be exactly the class, reference to the instance of which you’re assigning to the variable declared with var.

Java is a statically-typed language known for its verbosity and strict type checking. However, with the release of Java 10, a new feature called Local-Variable Type Inference was introduced, bringing the var keyword to the language and changing the way Java developers code. This article will explore the var keyword, illustrating its use cases and discussing its implications for Java coding practices.

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However, I prefer the clarity of specifying otherwise obscure types just to make things as clear as possible to the reader who may have to maintain my code in the future. I declare customerBalance as decimal to know its type for clarity. Cases where I do not use var, even though I still name the variable descriptively, are when the initializer is not clear. So there are definitely some compiler enforced rules about when to use Java’s var keyword. The idea to add var to the Java Language appeared around 2016 by the team of the OpenJDK.

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1. Many Java developers are used to just relying on the language’s type mechanism and not in the expressiveness of their code.
2. This can reduce readability for sure, BUT this is even more an opportunity to improve our codebase.
3. Let me know your thoughts 💭 and share your feedbacks 🖊️ in the comments.
4. Many languages, particularly scripting languages, have a loosely typed variable type named var.
5. In this case, it’s not clear what type x is, which can make the code harder to understand.

One of my recent experience which happened at work where my manager asked, “Why are you using var keyword everywhere in your code? I gave him detailed explanation about the usage of var keyword after which he was convinced and approved my PR. Later in the code, seeing processor vs someVerySpecificProcessor as the variable name makes a lot of difference. The type will be exactly the same of the value the variable gets assigned to. On this example, the path variable is of type Path, and the stream variable is of type InputStream. Michael Brennan, in his blog post Why You Should Always Use the ‘var’ Keyword in C#, makes some compelling points.

In addition to the other problems mentioned in this answer about var, there is another subtle issue. Although I agree with some of the arguments above, I have fairly specific rules that I use to determine whether I will use var or specify the type literally.