8.6.1. Variable declaration #

Before we learn how to declare variables and constants, let’s look at some variables and constants.

• Variable: the amount whose value may change during the running of the program is called variable. Such as: time, age.

• Second, the constant whose value will not change during the running of the program is called constant. Such as: numeric value 3, character’A’.

In Scala, use the keyword “var” to declare variables and the keyword “val” to declare constants.

An example of declaring a variable is as follows:

var myVar : String = "Foo"
var myVar : String = "Too"

Variables are defined above myVar , we can modify it.

An example of a declaration constant is as follows:

val myVal : String = "Foo"

The constant is defined above myVal , it cannot be modified. If the program tries to modify the constant myVal , the program will make an error in the compilation time.

8.6.2. Variable type declaration #

The type of the variable is declared before the equal sign after the variable name. The syntax format for defining the type of a variable is as follows:

var VariableName : DataType [=  Initial Value]

or

val VariableName : DataType [=  Initial Value]

8.6.3. Variable type reference #

Declaring variables and constants in Scala does not necessarily specify the data type, which is inferred from the initial value of the variable or constant without specifying the data type.

Therefore, if you declare a variable or constant without specifying the data type, you must give its initial value, otherwise an error will be reported.

var myVar = 10;
val myVal = "Hello, Scala!";

In the above example, myVar will be inferred as Int type, myVal will be inferred as String type.

8.6.4. Scala multiple variable declarations #

Scala supports multiple variable declarations:

val xmax, ymax = 100  // xmax, ymax declare as100

If the method return value is a tuple, we can use the val to declare a tuple:

scala> val pa = (40,"Foo")
pa: (Int, String) = (40,Foo)