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  }}