double inputData = new double[arrayLength]; 
// ... 給inputData賦值 
FastFourierTransformer fft = new FastFourierTransformer(DftNormalization.STANDARD); 
Complex[] result = fft.transform(inputData, TransformType.FORWARD); 

import org.apache.commons.math3.transform.DftNormalization; 
import org.apache.commons.math3.transform.FastFourierTransformer; 
import org.apache.commons.math3.transform.TransformType; 
interface TestCase 
{ 
  public Object run(List<Object> params) throws Exception; 
  public List<Object> getParams(); 
} 
class CalcFFT implements TestCase 
{ 
  public CalcFFT() 
  { 
   System.out.print("本算例用于計算快速傅立葉變換。正在初始化 計算數據(" + arrayLength + "點)... ..."); 
   inputData = new double[arrayLength]; 
   for (int index = 0; index < inputData.length; index++) 
   { 
     inputData[index] = (Math.random() - 0.5) * 100.0; 
   } 
   System.out.println("初始化完成"); 
  } 
  @Override 
  public List<Object> getParams() 
  { 
   return null; 
  } 
  @Override 
  public Object run(List<Object> params) throws Exception 
  { 
   FastFourierTransformer fft = new FastFourierTransformer(DftNormalization.STANDARD); 
   Complex[] result = fft.transform(inputData, TransformType.FORWARD); 
   return result; 
  } 
  private double[] inputData = null; 
  private final int arrayLength = 4 * 1024*1024; 
} 
public class TimeCostCalculator 
{ 
  public TimeCostCalculator() 
  { 
  } 
  /** 
  * 計算指定對象的運行時間開銷。 
  * 
  * @param testCase 指定被測對象。 
  * @return 返回sub.run的時間開銷，單位為s。 
  * @throws Exception 
  */ 
  public double calcTimeCost(TestCase testCase) throws Exception 
  { 
   List<Object> params = testCase.getParams(); 
   long startTime = System.nanoTime(); 
   testCase.run(params); 
   long stopTime = System.nanoTime(); 
   System.out.println("start: " + startTime + " / stop: " + stopTime); 
   double timeCost = (stopTime - startTime) * 1.0e-9; 
   //   double timeCost = BigDecimal.valueOf(stopTime - startTime, 9).doubleValue(); 
   return timeCost; 
  } 
  public static void main(String[] args) throws Exception 
  { 
   TimeCostCalculator tcc = new TimeCostCalculator(); 
   double timeCost; 
   System.out.println("--------------------------------------------------------------------------"); 
   timeCost = tcc.calcTimeCost(new CalcFFT()); 
   System.out.println("time cost is: " + timeCost + "s"); 
   System.out.println("--------------------------------------------------------------------------"); 
  } 
}