scala编程实战笔记(2-数值)

Char: 16位无符号Unicode
Byte: 8位有符号整数
Int： 32有符号整数
Long： 64有符号整数
Float : 32位单精度浮点型
Double：64双精度浮点

scala> Short.MinValue
Short.MinValue
res3: Short = -32768

scala> Long.MaxValue
Long.MaxValue
res4: Long = 9223372036854775807

其他更丰富的数值类型来自math库
日期数据：Joda time

2.1 字符串转数值

scala> "100".toInt  
"100".toInt
res7: Int = 100

scala> "100".toFloat
"100".toFloat
res8: Float = 100.0

scala> "foo".toInt
"foo".toInt
java.lang.NumberFormatException: For input string: "foo"

scala> BigDecimal("3.1415926")
BigDecimal("3.1415926")

• 处理基数和根

import java.lang.Integer
// 2进制
scala> Integer.parseInt("100", 2)      
Integer.parseInt("100", 2)
res12: Int = 4

隐式转换实现

scala> implicit class String2Int(s:String){
     | def toInt(radix:Int) = Integer.parseInt(s, radix)
     | }


scala> "100".toInt(2)   
"100".toInt(2)
res13: Int = 4

每次运行一个object必须定义main函数，另外一种方法参考http://spreadscala.iteye.com/blog/667534

object allrepl {
  def main(args:Array[String]):Unit={
    val x = "1000"
    println(x.toInt(2).getOrElse(0)) // out：8
    println("a".toInt(2).getOrElse(0)) //out:0
  }

  implicit class String2Int(s:String){
    // import java.lang.Integer
    def toInt(radix:Int):Option[Int] = {
      try {
        Some(Integer.parseInt(s, radix))
      } catch {
        case e: NumberFormatException => None
      }
    }
  }
}

对不同的数值类型之间相互转化的时候为了表面错误 判断方法：1.isValidByte

2.3 重载数据类型

在一个类中定义变量可以用占位符

cala> val a = 1
a: Int = 1

scala> val a:Long = 1
a: Long = 1

scala> val a = 1:Long
a: Long = 1

scala> val a = 1l
a: Long = 1

2.4 += 方法（不是操作符）

scala> var a = 1
a: Int = 1

scala> a += 1

scala> a
res5: Int = 2

+= -= *= /=

2.5 不同精度的比较运算设定误差范围

2.6 处理大数

scala> BigInt(123456789)
res0: scala.math.BigInt = 123456789
scala> BigDecimal(123456789)
res4: scala.math.BigDecimal = 123456789

scala> Double.PositiveInfinity
res2: Double = Infinity

scala> Double.NegativeInfinity
res3: Double = -Infinity

2.7 Random

scala> val r = scala.util.Random
r: util.Random.type = scala.util.Random$@759d26fb

scala> r.nextInt
res6: Int = 192058607
// 0-100
scala> r.nextInt(100)
res14: Int = 24

scala> r.nextDouble // 0-1
res8: Double = 0.5660426827712413

scala> r.nextFloat //0-1
res9: Float = 0.98220724

scala> r.setSeed(1000) //可在定义r的时候设定

2.8 数值区间

scala> 1 to 10
res15: scala.collection.immutable.Range.Inclusive = Range(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

scala> 1 to 10 by 2
res16: scala.collection.immutable.Range = Range(1, 3, 5, 7, 9)

scala> 1 until 10
res17: scala.collection.immutable.Range = Range(1, 2, 3, 4, 5, 6, 7, 8, 9)

scala> 1 until 10 toArray
warning: there was one feature warning; re-run with -feature for details
res18: Array[Int] = Array(1, 2, 3, 4, 5, 6, 7, 8, 9)

2.9 格式化数值金额

scala> import scala.math.Pi
import scala.math.Pi

scala> f"$Pi%1.3f"
res20: String = 3.142

scala> "%1.3f".format(Pi)
res21: String = 3.142

scala> import java.text.NumberFormat.getIntegerInstance
import java.text.NumberFormat.getIntegerInstance

scala> getIntegerInstance.format(1000000000)
res22: String = 1,000,000,000

scala> import java.text.NumberFormat.get
getAvailableLocales   getInstance          getNumberInstance    
getCurrencyInstance   getIntegerInstance   getPercentInstance   

• 货币

import java.util.{Currency, Locale}
val loc = new Locale("de", "DE")
val de = Currency.getInstance(loc)
val formater = java.text.NumberFormat.getCurrencyInstance
println(formater.format(10))  // 默认美元
formater.setCurrency(de)
println(formater.format(10))   // 欧元