测试某个方法运行时间的模板

//: io/MappedIO.java
import java.nio.*;
import java.nio.channels.*;
import java.io.*;

public class MappedIO {
  private static int numOfInts = 4000000;
  private static int numOfUbuffInts = 200000;
  private abstract static class Tester {
    private String name;
    public Tester(String name) { this.name = name; }
    public void runTest() {
      System.out.print(name + ": ");
      try {
        long start = System.nanoTime();
        test();
        double duration = System.nanoTime() - start;
        System.out.format("%.2f\n", duration/1.0e9);
      } catch(IOException e) {
        throw new RuntimeException(e);
      }
    }
    public abstract void test() throws IOException;
  }
  private static Tester[] tests = {
    new Tester("Stream Write") {
      public void test() throws IOException {
        DataOutputStream dos = new DataOutputStream(
          new BufferedOutputStream(
            new FileOutputStream(new File("temp.tmp"))));
        for(int i = 0; i < numOfInts; i++)
          dos.writeInt(i);
        dos.close();
      }
    },
    new Tester("Mapped Write") {
      public void test() throws IOException {
        FileChannel fc =
          new RandomAccessFile("temp.tmp", "rw")
          .getChannel();
        IntBuffer ib = fc.map(
          FileChannel.MapMode.READ_WRITE, 0, fc.size())
          .asIntBuffer();
        for(int i = 0; i < numOfInts; i++)
          ib.put(i);
        fc.close();
      }
    },
    new Tester("Stream Read") {
      public void test() throws IOException {
        DataInputStream dis = new DataInputStream(
          new BufferedInputStream(
            new FileInputStream("temp.tmp")));
        for(int i = 0; i < numOfInts; i++)
          dis.readInt();
        dis.close();
      }
    },
    new Tester("Mapped Read") {
      public void test() throws IOException {
        FileChannel fc = new FileInputStream(
          new File("temp.tmp")).getChannel();
        IntBuffer ib = fc.map(
          FileChannel.MapMode.READ_ONLY, 0, fc.size())
          .asIntBuffer();
        while(ib.hasRemaining())
          ib.get();
        fc.close();
      }
    },
    new Tester("Stream Read/Write") {
      public void test() throws IOException {
        RandomAccessFile raf = new RandomAccessFile(
          new File("temp.tmp"), "rw");
        raf.writeInt(1);
        for(int i = 0; i < numOfUbuffInts; i++) {
          raf.seek(raf.length() - 4);
          raf.writeInt(raf.readInt());
        }
        raf.close();
      }
    },
    new Tester("Mapped Read/Write") {
      public void test() throws IOException {
        FileChannel fc = new RandomAccessFile(
          new File("temp.tmp"), "rw").getChannel();
        IntBuffer ib = fc.map(
          FileChannel.MapMode.READ_WRITE, 0, fc.size())
          .asIntBuffer();
        ib.put(0);
        for(int i = 1; i < numOfUbuffInts; i++)
          ib.put(ib.get(i - 1));
        fc.close();
      }
    }
  };
  public static void main(String[] args) {
    for(Tester test : tests)
      test.runTest();
  }
} /* Output: (90% match)
Stream Write: 0.56
Mapped Write: 0.12
Stream Read: 0.80
Mapped Read: 0.07
Stream Read/Write: 5.32
Mapped Read/Write: 0.02
*///:~