One of scala variables and data types

1、 String output

（1） character string , adopt + Connection No

（2）printf usage ： character string , adopt % Pass value .

（3） String template （ Interpolation string ）： adopt $ Get the value of the variable

package com.atguigu.chapter02

object TestCharType {

    def main(args: Array[String]): Unit = {

        var name: String = "jinlian"
        var age: Int = 18

        //（1） character string , adopt + Connection No 
        println(name + " " + age)

        //（2）printf Usage string , adopt % Pass value .
        printf("name=%s age=%d\n", name, age)

        //（3） character string , adopt $ quote 
	// Multiline string , stay Scala in , You can use three double quotes to surround multiple lines of string .// Input content , With spaces 、\t And so on , As a result, the beginning of each line cannot be neatly aligned .
// application scala Of stripMargin Method , stay scala in stripMargin The default is “|” As a connector ,// Add a... Before the line header of multi line wrap “|” A symbol is enough .
        val s =
            """
              |select
              |    name,
              |    age
              |from user
              |where name="zhangsan"
            """.stripMargin
println(s)

// If you need to operate on variables , Then you can add ${}
        val s1 =
            s"""
              |select
              |    name,
              |    age
              |from user
              |where name="$name" and age=${age+2}
            """.stripMargin
        println(s1)

		  val s2 = s"name=$name"
        println(s2)
    }
}

2、 Keyboard entry

In programming , Need to receive the data input by the user , You can use keyboard input statements to get .

1） Basic grammar

StdIn.readLine()、StdIn.readShort()、StdIn.readDouble()

2） Case practice

demand ： Can receive user information from the console ,【 full name , Age , salary 】.

import scala.io.StdIn

object TestInput {

    def main(args: Array[String]): Unit = {

        // 1  Enter a name 
        println("input name:")
        var name = StdIn.readLine()

        // 2  Enter the age 
        println("input age:")
        var age = StdIn.readShort()

        // 3  Enter salary 
        println("input sal:")
        var sal = StdIn.readDouble()

        // 4  Print 
        println("name=" + name)
        println("age=" + age)
        println("sal=" + sal)
    }
}

3、 Type conversion

Cast

The reverse process of automatic type conversion , Convert a numeric type with high precision to a numeric type with low precision . When you use it, you need to add the forced conversion function , But it may cause accuracy reduction or overflow , Pay special attention to

Java  :  int num = (int)2.5
Scala :  var num : Int = 2.7.toInt

（1） Send the data from High precision Convert to Low precision , You need to use to cast

（2） The strong rotation symbol is only valid for the nearest operand , Curly braces are often used to increase priority

object TestForceTransfer {

    def main(args: Array[String]): Unit = {

        //（1） Convert data from high precision to low precision , You need to use to cast 
        var n1: Int = 2.5.toInt //  There is a loss of accuracy in this 
        
        //（2） The strong rotation symbol is only valid for the nearest operand , Curly braces are often used to increase priority 
        var r1: Int = 10 * 3.5.toInt + 6 * 1.5.toInt  // 10 *3 + 6*1 = 36
        var r2: Int = (10 * 3.5 + 6 * 1.5).toInt  // 44.0.toInt = 44

        println("r1=" + r1 + " r2=" + r2)
    }
}

Numerical types and String Conversion between types

1） Basic type rotation String type （ grammar ： Put the value of the basic type +"" that will do ）

（2）String Type to basic numeric type （ grammar ：s1.toInt、s1.toFloat、s1.toDouble、s1.toByte、s1.toLong、s1.toShort）

object TestStringTransfer {

    def main(args: Array[String]): Unit = {

        //（1） Basic type rotation String type （ grammar ： Put the value of the basic type +""  that will do ）
        var str1 : String = true + ""
        var str2 : String = 4.5 + ""
        var str3 : String = 100 +""

        //（2）String Type to basic numeric type （ grammar ： Call the relevant API）
        var s1 : String = "12"

        var n1 : Byte = s1.toByte
        var n2 : Short = s1.toShort
        var n3 : Int = s1.toInt
        var n4 : Long = s1.toLong
    }
}