1. Declare variables

1.1 Complete Definition

In Scala, we use val or var to define variables in the following syntax:

// val defines variables that cannot be reassigned
// var defines variables that can be reassigned
val/varVariable name: Variable type = initial value eg:val name:String = "jack"
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  • In Scala, the defined variable type is written after the variable name
  • Scala statements do not require a semicolon at the end
  • Preferred to usevalDefine a variable and use it only if it needs to be reassignedvar

1.2 Type inference – Define variables

In Scala, we do not specify the type of a variable when we define it. Scala specifies the type of a variable based on its value.

The sample

// This is the complete format for defining variables
scala> val name:String = "Jack"
name: String = Jack
// The type of the variable is omitted when defining the variable
scala> val name = "Jack"
name: String = Jack

scala> val age = 23
age: Int = 23
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1.3 Lazy assignment

When large data needs to be saved, but does not need to be loaded into JVM memory immediately. Lazy assignment can be used to improve efficiency.

Syntax format:

lazy val/varVariable name = expressionCopy the code

Reference code

scala> lazy val sql = """ | select | * | from | user | """
sql: String = <lazy>   // Is not loaded into the JVM
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Now that you know how to define variables, you may have noticed that in Scala, we don’t use semicolons after variable declarations and assignments. We only use semicolons when we use multiple statements in the same line of code

2. The string

2.1 Use double quotation marks

val/varVariable name = "string" eg:val name = "tom"
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2.2 Interpolation expression

val/varThe variable name =s"${variable/expression}The string"
eg:
val name = "jack"
val name1 = s"${name}"
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  • Before the string is defineds
  • In a string, you can useThe ${}To reference a variable or write an expression
scala> val name = "jack"
name: String = jack

scala> val age = 23
age: Int = 23
${$} = ${$}
scala> val log = s"name=${name}, age=${age}"
info: String = name=zhangsan, age=30
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2.3 Use triple quotation marks

val/varThe variable name =String 1 String 2""
// Can be used to store a large amount of data, but lazy assignment is not covered here
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