Scala学习-类,对象 - webdancer's Blog

Scala学习-类,对象

webdancer posted @ 2014年1月04日 01:39 in 编程语言 with tags scala , 4887 阅读

1.类:类是对象的蓝图,根据类,使用new关键字,就可以创建对象了。和Java一样,Scala的对象也包含:属性和方法。这部分和Java基本上相同。

  • 属性:默认是public的,使用private可以改变作用域;
  • 方法:定义类的方法与定义普通的相同;Scala没有静态方法。
    class ChecksumAccumulator {
      private var sum = 0
      def add(b: Byte) { sum += b }
      def checksum(): Int = ~ (sum & 0xFF) + 1
    }

在Scala的代码中,一个语句如果单独一行的话,可以不加分号,自动进行分号的推断;

  • class可以带参数,class Rational(a:Int,b:Int)
  • 使用override进行函数重载:
  • class Rational(a:Int,b:Int){
        overrride def toString = a + "/" + b
    }
  • preconditions:可以使用require()。
class Rational(a:Int, b:Int){
	require(b != 0)
	val  numer:Int = a
	val  demon:Int = b
	override def toString = a + "/" + b
	def add(that: Rational) = new Rational(
		a * that.demon + b * that.numer,
		b * that.demon
		)
}

2.使用object定义singleton 对象。

import scala.collection.mutable.Map

object ChecksumAccumulator {
  private val cache = Map[String, Int]()
  def calculate(s: String): Int =
    if (cache.contains(s))
      cache(s)
    else {
      val acc = new ChecksumAccumulator
      for (c <- s)
        acc.add(c.toByte)
      val cs = acc.checksum()
        cache += (s -> cs)
        cs
}
}

Singleton与class的名字相同,他们得放在同一源文件中,称为companion class 与companion object。不会创建新的类型;与class的名字不同,称为standalone对象,这种对象可以作为一个Scala程序的启动点。

 

3.Scala程序的启动类似Java,使用含有main方法的Singleton对象。

运行程序的话,首先使用scalac或是fsc进行编译,然后使用scala运行(不含后缀),终于Java的命令行是类似的。

也可是使用Application traits来启动程序,不过这种方法仅仅用在一些简单的,单线程程序中。

 

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