Java多線程讀文件比單線程提高效率的實例

假設有兩個文本文件Arrays-1.txt和Arrays-2.txt,內容格式如下:

1

2

3

4

.

.

.

用單線程分別讀這兩個文件並求和,花費時間time1;用兩個線程同時讀這兩個文件並求和,花費時間time2;結果顯示:time1>time2,因此說明多線程可以提高效率.測試計算機配置:雙核Intel Core i3 cpu550,4G RAM

import java.io.*;
public class ThreadsSum6{
    public static void main(String[] args) throws IOException {
       String str;
       long sum1=0;
       long start = System.currentTimeMillis();
       FileReader fr=new FileReader("arrays-1.txt");
       //建立文件輸入流
       BufferedReader br=new BufferedReader(fr);
       //建立緩沖輸入流

       while ((str=br.readLine())!=null) {
             sum1+=Integer.parseInt(str);
       }
       fr=new FileReader("arrays-2.txt");
       br=new BufferedReader(fr);
       while ((str=br.readLine())!=null) {
             sum1+=Integer.parseInt(str);
       }
       fr.close();
       long end = System.currentTimeMillis();
       System.out.println("sum1="+sum1);
       System.out.println("time1="+(end - start));

       start = System.currentTimeMillis();
       ReadFileThread th1=new ReadFileThread("arrays-1.txt");
       ReadFileThread th2=new ReadFileThread("arrays-2.txt");
       th1.start();
       th2.start();
       try{//等待線程結束
        th1.join();
        th2.join();
       }catch(Exception e){}
       long sum2=th1.getSum()+th2.getSum();
       end = System.currentTimeMillis();

       System.out.println("sum2="+sum2);
       System.out.println("time2="+(end - start));
   }
}
class ReadFileThread extends Thread{
    long sum=0;
    FileReader fr;
    BufferedReader br;
    String str;
    public ReadFileThread(String fileName){
        try{
            fr=new FileReader(fileName);
            //建立文件輸入流
            br=new BufferedReader(fr);
            //建立緩沖輸入流
        }
        catch(Exception e){System.out.println("error1");}
    }
    public void run(){
        try{
             while((str=br.readLine())!=null) {
                sum+=Integer.parseInt(str);
             }
             fr.close();                
        }
        catch(Exception e){System.out.println("error2");}
    }
    long getSum(){
        return sum;
    }
}