Local variable type inference in Java 10: How to use final var keyword in lambda expression

Local variable type inference in Java 10: How to use the final var keyword in lambda expressions

With the release of Java 10, a new feature-local variable type inference has been introduced. This feature allows you to use the var keyword instead of a specific type when declaring local variables, and the compiler will automatically infer the variable type based on the variable's initialization expression. This feature not only simplifies the code, but also enhances the readability and maintainability of the code. In this article, we will explore how to use the final var keyword in lambda expressions to achieve cleaner code.

First, let’s take a look at how local variable type inference works in Java 10. Here is a simple example:

final var message = "Hello, World!";
System.out.println(message);

In the above code, we use var The keyword declares a variable named message and initializes it to the string "Hello, World!". The compiler will infer that the message type is String based on the initialization expression, so there is no need to explicitly specify the type. We can then use the message variable like any other type.

Now, let us explore how to use the final var keyword in lambda expressions. Here is an example using lambda expressions:

final var numbers = List.of(1, 2, 3, 4, 5);
numbers.forEach((final var number) -> System.out.println(number));

In the above code, we declared a variable named numbers using the var keyword and initialized it to a list containing five integers. We then call the list's forEach method, passing a lambda expression as argument. Inside the lambda expression, we declare a variable called number using the final var keyword and initialize it to each element in the list. The compiler will infer that the type of number is an integer based on the initialization expression, so there is no need to explicitly specify the type. We can then use the number variable in a lambda expression, for example to output its value.

By using the final var keyword in lambda expressions, we can avoid repeatedly writing the variable type in the code, making the code more concise and readable. This is especially useful when you need to write a lot of code that uses lambda expressions.

However, it should be noted that when using the final var keyword in a lambda expression, the variable must be of final type. This is because the variables referenced in the lambda expression must be immutable to ensure that they remain unchanged during the execution of the lambda expression. If you try to modify the value of a final var variable, the compiler will report an error.

Although using the final var keyword in lambda expressions makes the code more concise, you also need to pay attention to keeping the code readable and maintainable. When naming variables, you should choose meaningful names so that readers can understand the meaning of the variables and the code can be easily maintained.

In summary, local variable type inference in Java 10 provides us with a more concise and readable way of writing code. By using the final var keyword in lambda expressions, we can avoid repeatedly writing the type of the variable, making the code more concise and readable. However, it is important to note that when using the final var keyword in a lambda expression, the variable must be of type final. In actual development, we should weigh the balance between simplicity and readability brought about by using the final var keyword.

I hope this article can help you better understand local variable type inference in Java 10 and use the final var keyword more flexibly in code writing.

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