jdk7 fork/join 性能测试-不如for循环~~很奇怪

两种方法计算 Fibonacci

package jdk7;

import java.util.concurrent.RecursiveAction;
import java.util.Date;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.ForkJoinTask;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;

public  class Fibonacci extends RecursiveTask<Long>{ 
    final int n; 
   
    Fibonacci(int n) { 
        this.n = n; 
    } 
 
    private Long compute(int small) { 
        final Long[] results = { 1l, 1l, 2l, 3l, 5l, 8l, 13l, 21l, 34l, 55l, 89l }; 
        return results[small]; 
    } 
 
    public Long compute() { 
        if (n <= 10) { 
            return compute(n); 
        } 
// 分别计算每个 列表的 数据
//        Fibonacci f1 = new Fibonacci(n - 1); 
//        Fibonacci f2 = new Fibonacci(n - 2); 
////        System.out.println("fork new thread for " + (n - 1)); 
//        f1.fork(); 
////        System.out.println("fork new thread for " + (n - 2)); 
//        f2.fork(); 
//        return f1.join() + f2.join();
       
       
        Fibonacci f1 = new Fibonacci(n - 1); 
        f1.fork(); 
        Fibonacci f2 = new Fibonacci(n - 2); 
        return f2.compute() + f1.join(); 
    }
   
    //非递归实现
public Long sum() {
long f1 = 1, f2 = 1;
long m = 0;
if (n <= 2) {
return 1l;
} else {
for (int i = 3; i <= n; i++) {
m = f1 + f2;
f2 = f1;
f1 = m;
}
return m;
}
}
   
    public static void main(String args[]) throws InterruptedException, ExecutionException{ 
//    Fibonacci f = new Fibonacci(100);
//   
//    long t1 = new Date().getTime();
//    Integer i = f.compute();
//    long t2 = new Date().getTime();
//    System.out.println(i+"耗时:"+(t2-t1)); 
    long t1 = new Date().getTime();
    ForkJoinTask<Long> fjt = new Fibonacci(41); 
        ForkJoinPool fjpool = new ForkJoinPool(); 
        fjpool.execute(fjt); 
        Long resultInt = fjt.get(); 
        long t2 = new Date().getTime();
       
        Long j = new Fibonacci(42).sum();
        long t3 = new Date().getTime();
        System.out.println(resultInt+"耗时:"+(t2-t1)); 
        System.out.println(j+"耗时:"+(t3-t2)); 
    }
 
} 

结果如下：
fork/join 性能不如 for循环

267914296耗时:417
267914296耗时:0