Scala学习笔记——函数式对象

用创建一个函数式对象（类Rational）的过程来说明

类Rational是一种表示有理数（Rational number）的类

package com.scala.first

/**
  * Created by common on 17-4-3.
  */
object Rational {
  def main(args: Array[String]) {

    var r1 = new Rational(1, 2)
    var r2 = new Rational(1)
    System.out.println(r1.toString)
    System.out.println(r1.add(r2).toString)
    var r3 = new Rational(2, 2)
    System.out.println(r3)
    System.out.println(r1 + r3)
  }
}

class Rational(n: Int, d: Int) {
  //检查先决条件，不符合先决条件将抛出IllegalArgumentException
  require(d != 0)
  //最大公约数
  private val g = gcd(n.abs, d.abs)

  private def gcd(a: Int, b: Int): Int = {
    if (b == 0) a else gcd(b, a % b)
  }

  //进行约分
  val numer: Int = n / g
  val denom: Int = d / g

  //辅助构造器
  def this(n: Int) = this(n, 1)

  //定义操作符
  def +(that: Rational): Rational = {
    new Rational(
      numer * that.denom + that.numer * denom,
      denom * that.denom
    )
  }

  //方法重载
  def +(i: Int): Rational = {
    new Rational(
      numer + i * denom, denom
    )
  }

  def *(that: Rational): Rational = {
    new Rational(
      numer * that.numer,
      denom * that.denom
    )
  }

  //方法重载
  override def toString = numer + "/" + denom

  //定义方法
  def add(that: Rational): Rational = {
    new Rational(
      numer * that.denom + that.numer * denom,
      denom * that.denom
    )
  }

  //定义方法，自指向this可写可不写
  def lessThan(that: Rational): Boolean = {
    this.numer * that.denom < that.numer * this.denom
  }

}