Scala series (2) – Data types, conditional expressions

1. Data types and operators

1.1 Data Types

Notice the difference between Scala types and Java

[!NOTE]

1. All types in Scala begin with a capital letter
2. Use plasticIntInstead of an Integer
3. Variables defined in Scala can be typed without being written, allowing the Scala compiler to infer automatically

1.2 the operator

• Scala does not have the ++ and — operators

• Unlike Java, in Scala, you can use ==,! Eq is used when comparing reference values

Reference code

val str1 = "abc"
val str2 = str1 + ""
str1 == str2   true
str1.eq(str2)   false
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1.3 Scala Type Hierarchy

Conditional expressions

2.1 Has a return value

[!NOTE]

• In Scala, conditional expressions also return values
• In Scala, there are no ternary expressions and you can use if expressions instead

scala> val age:Int = 20
age: Int = 20
// The result expression can return the result
scala> val result:Boolean = if(age == 20) true else false
result: Boolean = true

scala> print(result)
true
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2.2 Block expressions

• In Scala, {} is used to represent a block expression
• Like if expressions, block expressions have values
• The value is the value of the last expression

// return null because there is no last expression
scala> val a = {
     | println("jack")
     | }
jack
a: Unit = ()

// return the last value of 1 + 1
scala> val b = {
     | println("haode")
     | 1 + 1
     | }
haode
b: Int = 2
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3. The cycle

3.1 For Expression

grammar

for(I <- expression/array/set) {/ / expression
}
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3.1.1 Simple Loop

Walk through the numbers 1 to 10

// we can get the numbers from 1 to 10 first, and then iterate
scala> val nums = 1.to(10)                                                              
nums: scala.collection.immutable.Range.Inclusive = Range(1.2.3.4.5.6.7.8.9.10) 
                                                                                        
scala> for(i <- nums) println(i)      

// 2, use infix call method (later chapter will talk about, here is not introduced to everyone)
scala> for(i <- 1 to 10) println(i)
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3.1.2 Nested loops

for(i <- 1 to 3; j <- 1 to 5) {print("*");if(j == 5) println(""} result: ***** ***** *****Copy the code

3.1.3 guard

A guard is the ability to add an if statement to a for expression

grammar

for(I <- expression/array/setifExpression) {/ / expression
}
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// Add a guard to print a number divisible by 3
for(i <- 1 to 10 if i % 3= =0) println(i)
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3.1.4 Derivation for

• In the future, you can use the for derivation to generate a new set (a set of data)

• In the body of a for loop, we can use yield expressions to build a collection. We call for-expressions that use yield expressions derivations

// For: the for expression starts with yield and builds a collection
scala> val a = for(i <- 1 to 10) yield i * 10
a: scala.collection.immutable.IndexedSeq[Int] = Vector(10.20.30.40.50.60.70.80.90.100)
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3.2 the while loop

A while loop in Scala is the same as a while loop in Java

scala> var i = 1
i: Int = 1

scala> while(i <= 10) {
     | println(i)
     | i = i+1|}Copy the code

3.3 break and continue

• In scala, the break/continue keyword similar to Java and C++ has been removed
• If you must use break/continue, you need to use the breable and break methods of the break class of the Scala.util. control package.

3.3.1 implementation break

// import Break in scala.util. Control
import scala.util.control.Breaks. _// 2. Wrap the for expression with breakable
breakable{
    for(i <- 1 to 100) {
// 3. Add the 'break()' method call where the for expression needs to exit the loop
        if(i >= 50) break(a)else println(i)
    }
}
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3.3.2 rainfall distribution on 10-12 realize the continue

// import Break in scala.util. Control
import scala.util.control.Breaks. _// 2. Wrap the body of the for loop with breakable
for(i <- 1 to 100 ) {
    breakable{
        if(i % 10= =0) break(a)else println(i)
    }
}
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