Local variable type inference in Java 10: How to simplify your code using var keyword

Local variable type inference in Java 10: How to use the var keyword to simplify code

Introduction:
In Java 10, the feature of local variable type inference is introduced. By using the var keyword, Can simplify the coding process. This article will introduce the use of the var keyword and demonstrate its effect of simplifying the code through sample code.

1. What is local variable type inference?
Local variable type inference means that when declaring local variables, you can use the var keyword instead of explicit type declaration. The compiler will infer the type of the variable based on the type of the assignment expression to simplify code writing.

2. How to use the var keyword

1. Declaration syntax
   The syntax for using the var keyword to declare a local variable is as follows:
   var variable name = expression ;
2. Variable initialization
   When using the var keyword to declare a local variable, it must be initialized. The compiler infers the type of a variable from the type of the assignment expression.
3. Inference rules
   The compiler infers the type of the variable based on the type of the assignment expression. The inference rules are as follows:
4. If the type of the assignment expression is clear (such as int, String, etc.) , the compiler will infer the variable's type to that type.
5. If the assignment expression is a generic method call, the compiler will infer the type of the variable to the type of the actual type parameter.
6. If the assignment expression is a lambda expression, the compiler will infer the type of the variable to the corresponding function interface type.
7. If the type of the assignment expression is a constructor of a collection or array of unknown type, the compiler will infer the type of the variable to the type of the collection or array.

3. Examples of using the var keyword to simplify the code
The following is a few example codes to demonstrate the effect of using the var keyword to simplify the code.

1. Basic type variable declaration
   The code using the var keyword to declare a basic type variable is as follows:

   var num = 10;
   System.out.println(num);

   The above code is equivalent to:

   int num = 10;
   System.out.println(num);

2. Reference type variable declaration
   The code using the var keyword to declare a reference type variable is as follows:

   var name = "Java";
   System.out.println(name);

   The above code is equivalent to:

   String name = "Java";
   System.out.println(name);

3. Collection type variable declaration
   The code using the var keyword to declare a collection type variable is as follows:

   var list = new ArrayList<String>();
   list.add("Java");
   System.out.println(list.get(0));

   The above code is equivalent to:

   ArrayList<String> list = new ArrayList<>();
   list.add("Java");
   System.out.println(list.get(0));

4. lambda expression variable declaration
   The code to declare a lambda expression variable using the var keyword is as follows:

   var runnable = (Runnable) () -> {
    System.out.println("Hello Java 10!");
   };
   runnable.run();

   The above code is equivalent to:

   Runnable runnable = (Runnable) () -> {
    System.out.println("Hello Java 10!");
   };
   runnable.run();

Summary:
By using the var keyword, you can simplify the code writing process, especially during the declaration of local variables. However, in actual use, the var keyword needs to be used with caution to avoid reducing the readability of the code. In the case of strong readability, you can use the var keyword to simplify the code and improve development efficiency.

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