统计方法运行时间【Java实现】

接口Command：定义命令的执行操作

package common;

public interface Command {

    // 运行方法
    void run();

}

　CommandRuntime 类:统计命令运行时间，使用命令模式

package common;

public class CommandRuntime {

    private Command command;

    public CommandRuntime(Command command)
    {
        this.command = command;
    }

    public long runtime() {

        long start = System.currentTimeMillis();
        command.run();
        long end = System.currentTimeMillis();

        return end-start;
    }

}

CombinationCommand:  解决组合问题的命令， 采用类适配器模式：

package algorithm.problems;

import algorithm.permutation.Combination;

import common.Command;

public class CombinationCommand extends Combination implements Command {

    public CombinationCommand(int n) {
        super(n);
    }

    public void run() {
        solution();
    }

}

CombinationRuntime: 测量组合问题的运行时间

package algorithm.problems;

import java.io.BufferedWriter;
import java.io.FileWriter;
import java.io.IOException;

import common.CommandRuntime;

public class CombinationRuntime {

    public static void main(String[] args)
    {
        try {
            BufferedWriter fileWriter = new BufferedWriter(new FileWriter("runtime.txt"));
            fileWriter.write("runtime: ");
            fileWriter.newLine();
            for (int i=1; i < 30; i++) {
                   CommandRuntime comRuntime = new CommandRuntime(new CombinationCommand(i));
                   long runtime = comRuntime.runtime();
                   fileWriter.write( "n = " + i + " : " + runtime + " ms");
                   fileWriter.newLine();
            }
            System.out.println("over.");
            fileWriter.close();

        } catch (IOException e) {
            e.printStackTrace();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

}

　　另外一种使用反射机制实现的运行时间测量框架：

package common;

import java.lang.reflect.Constructor;
import java.lang.reflect.Method;

public class RuntimeMeasurement {

    public RuntimeMeasurement(int maxsize) {
        this.maxsize = maxsize;
        time = new double[maxsize];
    }

    // 问题最大规模: 以 10 的 size 次幂计
    private int maxsize ;

    // 运行时间以 ms 计
    private double[] time ;

    /**
     * measureTime : 对指定类型的对象调用指定参数列表的指定方法，并测量其运行时间
     * @param type  指定对象类型，必须有一个 参数类型为 int 的公共构造器方法
     * @param methodName  指定测试方法名称，要求是空参数列表
     */
    public void measureTime(Class<?> type, String methodName)
    {
        try {
             Constructor<?> con = type.getConstructor(int.class);
             Method testMethod = null;
             for (int i = 0; i < time.length; i++) {
                  Object obj = con.newInstance(power10(i+1));
                  testMethod = type.getMethod(methodName, new Class<?>[]{});
                  long start = System.nanoTime();
                  testMethod.invoke(obj, new Object[] {});
                  long end = System.nanoTime();
                  time[i] =  ((end - start) / (double)1000000) ;
                }

        } catch (Exception e) {
                e.printStackTrace();
                System.out.println(e.getMessage());
        }

    }

    /**
     * showTime : 显示已经测量获得的运行时间，在 measureTime 方法调用后调用该方法。
     */
    public void showTime()
    {
        for (int i=0; i < time.length; i++) {
            System.out.printf("n = %12d : " , power10(i+1));
            System.out.printf("%12.3f\n", time[i]);
        }
    }

    private int power10(int n)
    {
        int result = 1;
        while (n > 0) {
            result *= 10;
            n--;
        }
        return result;
    }

}