有趣的优化问题

先上环境

$ java -version
java version "1.8.0_171"
Java(TM) SE Runtime Environment (build 1.8.0_171-b11)
Java HotSpot(TM) 64-Bit Server VM (build 25.171-b11, mixed mode)

测试代码

public class DemoTest {  
    interface Op {  
        int operate(int d);  
    }  
  
    static class M1 implements Op {  
        @Override  
        public int operate(int d) {  
            return d + 1;  
        }  
    }  
  
    static class M2 implements Op {  
        @Override  
        public int operate(int d) {  
            return d + 1;  
        }  
    }  
  
    public static void callMillion(Op op) {  
        int d = 0;  
        for (int i = 0; i < 1000000; i++) {  
            op.operate(d);  
        }  
    }  
  
    public static void main(String[] args) {  
        CyclicBarrier cyclicBarrier = new CyclicBarrier(3);  
        ExecutorService executorService = Executors.newFixedThreadPool(3);  
        // 执行 100W 次 M1
        executorService.submit(() -> {  
            try {  
                cyclicBarrier.await();  
            } catch (InterruptedException | BrokenBarrierException e) {  
                e.printStackTrace();  
            }  
            long start = System.nanoTime();  
            callMillion(new M1());  
            long cost = System.nanoTime() - start;  
            System.out.println("start:" + (start / 1000000) + ", test1: " + cost);  
        });  
        // 执行 100W 次 M2
        executorService.submit(() -> {  
            try {  
                cyclicBarrier.await();  
            } catch (InterruptedException | BrokenBarrierException e) {  
                e.printStackTrace();  
            }  
            long start = System.nanoTime();  
            callMillion(new M2());  
            long cost = System.nanoTime() - start;  
            System.out.println("start:" + (start / 1000000) + ", test2: " + cost);  
        });  
        // 执行 100W 次真实逻辑
        executorService.submit(() -> {  
            try {  
                cyclicBarrier.await();  
            } catch (InterruptedException | BrokenBarrierException e) {  
                e.printStackTrace();  
            }  
            long start = System.nanoTime();  
            int d = 0;  
            for (int i = 0; i < 1000000; i++) {  
                d += 1;  
            }  
            long cost = System.nanoTime() - start;  
            System.out.println("start:" + (start / 1000000) + ", test3: " + cost);  
        });  
        executorService.shutdown();  
    }  
}

可以先心里想一下答案是什么，然后再验证一下，如果出乎了你的意料，欢迎讨论