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Java var Best Practices

Post Date: 18 Oct 2023


Java, with each release and update, continually evolves to simplify the developer’s journey while preserving its core tenets of readability and robustness. One of the notable introductions in Java 10 was the var keyword. As with most new features, it sparked debates and questions regarding its efficacy and best practices.

The Essence of the var Keyword in Java

The var keyword in Java is primarily a tool for type inference, allowing the Java compiler to infer the type of the variable from its initializer. This means that instead of explicitly declaring the type, we let the compiler decide based on the context.

For example:

var name = "John Doe";  // inferred as String
var age = 25;  // inferred as int

At compile time, the above code translates to:

String name = "John Doe";
int age = 25;

However, this feature is not a sign of Java becoming a dynamic language like JavaScript. It’s a convenience, not a transition.

Benefits of Using var

1. Enhanced Readability

Often, the argument for using the var keyword centers around the readability of the code. When used judiciously, it can make the code more legible and user-friendly. Especially in scenarios where the right-hand side of the declaration clearly reveals the type, adding explicit types might be redundant.

2. Simplification of Generic Types

In modern Java coding, there are situations where generic types can get overly verbose. With var, you can simplify the declaration without sacrificing clarity:

Map<String, List<String>> map = new HashMap<>();

With var, this becomes:

var map = new HashMap<String, List<String>>();

3. Encourages Use of Interface Instead of Implementation

When you employ var, it subtly nudges developers to program for an interface rather than for a specific implementation. This adheres to one of the popular design patterns and promotes better software maintenance.

Misconceptions and Guidelines

It’s Not a Transition to a Dynamic Language

Although languages like JavaScript, Scala, and TypeScript offer type inference, Java remains staunchly static. var does not change this. As evident in the context provided, var does not infer types at runtime but rather at compile time. Therefore, Java maintains its status as a static language, and concerns about it becoming akin to JS or ECMAScript are misplaced.

Where You Can’t Use var

While var is undeniably convenient, there are cases where its usage is inappropriate or even prohibited. For instance, you cannot initialize a var with null because the compiler wouldn’t have enough context to determine its type.

// This will cause a compile-time error.
var something = null;

Moreover, when considering software maintenance, overuse or misuse of var can lead to less understandable code, complicating debugging, code refactoring, and bug fixing.

Best Practices

Favor Clarity Over Brevity

If using var makes the code less understandable, prefer explicit typing.

Here’s an example illustrating the concept that “Clarity is Key” when using the var keyword in Java:

public class ClarityExample {
    public static void main(String[] args) {
        // Without var, the type is explicit
        String greeting = "Hello, Java!";

        // With var, the type is still clear
        var message = "Hello, Java!";


In this example, we have two variables: greeting and message, both initialized with the same string, “Hello, Java!”. The first variable, greeting, is declared explicitly with its type (String). The second variable, message, uses the var keyword.

Despite using var, the type of message remains clear because the assignment “Hello, Java!” makes it evident that message is of type String. This demonstrates that in cases where the type is obvious from the initialization value, using var can make the code more concise without sacrificing clarity.

Keeping Java’s Static Typing Intact

One significant point in favor of var is that it helps maintain Java’s status as a statically typed language. In some scenarios, like when dealing with null, var is not allowed. While this may seem restrictive, it’s actually a good thing. Allowing var in such cases would undermine Java’s commitment to strong typing. Fortunately, this restriction is the exception rather than the rule, and in most everyday coding situations, you’ll find that var can be used quite liberally.

Here’s an illustrative example to support the point mentioned:

Example: var and Null Initialization

In dynamically typed languages, it’s possible to have a variable without a specific type until runtime. However, Java’s static typing prevents such ambiguity. With the introduction of var, this fundamental principle remains intact.

Incorrect Use of var

// This will throw a compile-time error
var unknownType = null;

In the example above, attempting to initialize a var variable with null is prohibited. The Java compiler cannot infer a type solely from null, which would defy the concept of static typing.

Correct Use of var

var personName = "John Doe";
var dateOfBirth = LocalDate.of(1990, 1, 15);

In these instances, the compiler can easily infer the types (String and LocalDate, respectively) based on the assigned values, ensuring that static typing remains consistent throughout the codebase.

The bottom line is, while var brings a level of flexibility and conciseness to Java, it doesn’t compromise the language’s core principle of being statically typed.

Descriptive Variable Names

Descriptive variable names are essential, especially when using the var keyword, as they provide context and clarity to what the variable represents. Adhering to this practice aligns with the principles of “clean code”, which emphasizes that code should be easy to understand, modify, and maintain by anyone reading it, not just its original author. By choosing descriptive names, developers contribute to a codebase that’s more sustainable and collaborative.

Non-descriptive Variable Names with var

var a = "John Doe";
var b = LocalDate.of(1990, 1, 15);
var c = new ArrayList<String>();

In the above example, variable names a, b, and c do not provide any context or meaning. A developer reading this code would have to spend extra effort figuring out the purpose of each variable.

Descriptive Variable Names with var

var personName = "John Doe";
var dateOfBirth = LocalDate.of(1990, 1, 15);
var listOfTasks = new ArrayList<String>();

Here, each variable name (personName, dateOfBirth, and listOfTasks) explicitly describes its purpose or the kind of data it holds, making the code more readable and self-explanatory.

Context is Key

The context in which you use var is crucial. Clear and meaningful variable names, along with well-designed code, can make all the difference. For instance, if you have a method like .getPerson(), using var to declare a variable assigned from this method call doesn’t hinder understanding; it enhances it. The reader can reasonably infer that the variable is of type Person.

Let’s delve into a practical example to elucidate the point:

Example: Using var with Clear Context

In a class dealing with person management, let’s assume there is a method getPerson() that retrieves a Person object from a database or a service:

public Person getPerson(int id) {
    // Logic to fetch the person from a database or service using the id

When calling this method and storing the result in a variable, using var becomes quite intuitive:

var retrievedPerson = getPerson(12345);

In this context, even though we’re using var, it’s evident that retrievedPerson is of type Person. The method’s name, getPerson(), provides a clear context. Thus, there’s no ambiguity or loss of clarity for a developer reading the code.

However, if the method name was ambiguous like getData(12345), using var might not be as clear since the context wouldn’t readily indicate the type of the returned data. This is why well-named methods and variables are pivotal when leveraging the var keyword in Java.

Avoid Initializing with Complex Expressions

Initializing var with complex expressions can lead to reduced readability, as the inferred type might not be immediately evident.

Complex Initialization with var

var result = someList.stream()
        .filter(obj -> obj.isActive())

In the above example, a developer unfamiliar with the code might wonder:

  1. What type is someList?
  2. What does the filtered list contain?
  3. What is the final type of result?

While a seasoned developer can infer that result is an int due to the mapToInt and sum methods, for someone less familiar with Java streams, this might not be immediately clear.

More Clear Initialization

A clearer approach would be to break down the expression:

var activeObjects = someList.stream()
        .filter(obj -> obj.isActive())
var summedValue = activeObjects.stream()

Here, the expressions are simplified, and each variable has a clear and specific purpose, making the code more understandable.

Always Refer to the Guidelines

Adhering to the recommended coding rules and standards ensures that you use var efficiently without sacrificing readability.

In Conclusion

The introduction of the var keyword is a testament to Java’s adaptability and its endeavor to simplify and refine coding without compromising on its foundational principles. While it offers a streamlined approach, developers should use it judiciously, always prioritizing code clarity and maintainability. As with all tools, it’s not about whether it’s inherently good or evil—it’s about how you use it.

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