Scala functional style deferent from java OOP(特点)
该程序通过一段斐波那契数列的计算,比较一下Scala的函数式编程与java的面向对象的不同。
不多说了上代码。
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/* * To change this template, choose Tools | Templates * and open the template in the editor. */// "_"符号相当于java的* 比如是java.util.* import scala.actors._import scala.actors.Actor._import scala.util.Randomimport java.util.Dateobject Actors{ def main(args: Array[String]){ val actors = new Array[Actor](250000) for(i <- 0 to 249999){ //actor循环,高并发模型 actors(i) = actor{ loop{ react{ case fibNum: Int => calculate(fibNum, i) } } } } val random = new Random() for(a <- actors){ a ! random.nextInt(25) } } //执行打印 def calculate(fibNum: Int, i: Int) = { val answer = fibonacci(fibNum) if((i + 1) % 1000 == 0){ val idPlusOne = i + 1 println("The " + fibNum + "th fibonacci number is " + answer + " (thread: " + idPlusOne + ")") } if((i + 1) % 250000 == 0){ System.exit(0) } } //斐波那契数列匹配,是不是比java定义同样的方法简单多了？连变量都不要了。 def fibonacci( n: Int): Int = n match { case 0 => 0 case 1 => 1 case _ => fibonacci(n -1) + fibonacci(n - 2) }}?
再看看实现同样功能的java代码吧
import java.util.Date;import java.util.Random; public class JavaThreads extends Thread{ private static int THREAD_COUNT = 250000; private int fibNum; private int jid; public JavaThreads(int id, int fibNum){ this.jid = id; this.fibNum = fibNum; } public void run(){ int answer = fibonacci(fibNum); if(this.jid % 1000 == 0){ System.out.println("The " + fibNum + "th fibonacci number is " + answer + " (thread: " + this.jid + ")"); } } private int fibonacci(int i){ if(i < 2){ return i;} return fibonacci(i - 1) + fibonacci(i - 2); } public int getJid(){ return jid; } public void setJid(int jid){ this.jid = jid; } public int getFibNum(){ return fibNum; } public void setFibNum(int fibNum){ this.fibNum = fibNum; } public static void main(String args[]){ Date beginDate = new Date(); long memoryBegin = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory(); JavaThreads threads[] = new JavaThreads[THREAD_COUNT]; Random random = new Random(); for(int i = 0; i < THREAD_COUNT; i++){ threads[i] = new JavaThreads(i, random.nextInt(25)); } for(JavaThreads thread : threads){ thread.start(); } long memoryEnd = Runtime.getRuntime().totalMemory() - Runtime.getRuntime().freeMemory(); Date endDate = new Date(); System.out.println("Completed in " + ((endDate.getTime() - beginDate.getTime())/1000) + " seconds"); System.out.println("Used memory: " + (memoryEnd - memoryBegin)); } }?
相信上面的java代码大家很熟悉了。该段demo其实展现了scala很多特性
比如:
1、object Actors {} 相当与 java的单例设计.没有过多的说明只是定义类的类型不一样,省去了java中构造私有的步骤达到同样的功能。
2、scala由于是基于JVM的,可以调用java类库. 代码中 import java.util.Date ;
3、val变量相当于java中的常量了(貌似是众多函数式编程语言的使用规范).var可以是变量,但用的少。
4、循环结构简洁、易于明白脱离了数组下标所带来的麻烦,for(i <- 0 to 249999).
5、actors高并发模型是借鉴Erlang,在公司的时候、服务器后台使用的比较多。
6、类型自动推测。把函数当返回值使用。
说实话,scala的特点真的蛮多的.特别是和java放在一起。相信你即使没有学过scala，只要有java基础一定看的出大概了。怎么样心动了么？
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