看到了一些有趣的java 代码

1. 　enum　居然有public static void main(String[] args) ,该例子出自wicked cool java.

package hezhb_test;

//enum Dessert{PIE, CAKE, ICECREAM, BROWNIE};
enum FruitCategory{SWEET, CITRUS,SMELLY,UNKNOWN};
//enum Fruit{APPLE, ORANGE,GRAPEFRUIT,BANANA,DURIAN};

public enum MyFruit {

    APPLE{ FruitCategory getCategory(){
            return FruitCategory.SWEET;}
    },

    ORANGE{ FruitCategory getCategory(){
        return FruitCategory.CITRUS;}
    },

    GRAPEFRUIT{ FruitCategory getCategory(){
        return FruitCategory.CITRUS;}
    },

    BANANA { FruitCategory getCategory(){
        return FruitCategory.SWEET;}
    },

    DURIAN { FruitCategory getCategory(){
        return FruitCategory.SMELLY;}
    };

    abstract FruitCategory getCategory();

    public static void main(String[] args){
        MyFruit a = MyFruit.APPLE;
        //toString() returns "APPLE"
        System.out.println("The toString(); for a:"+a);
        //getCategory() returns "SWEET"
        System.out.println("a.getCatetory() is: "+a.getCategory());
        for(MyFruit f: MyFruit.values()){
            System.out.println("Fruit is :"+f);
        }
    }
}

2.  写个ThreadSleepDemo看看纳秒的精度，感觉ms和ns的精度有点吓人啊。根本是无法控制的，误差肯定会很大.
当前我犯了个错误而eclipse居然没发现，我知道long在c里面printf要用%ld，我就顺手写了个%ld,然后执行出错，但是eclipse不认为我有错。
报错是这个:

Exception in thread "main" java.util.UnknownFormatConversionException: Conversion = 'l'

后来我改成了%d才能执行，看了看这个，发现java 没有%ld

package multithread;

public class ThreadSleepDemo {
    public static void main(String[] args){
        Runnable r = ()->{
            try{
                Thread.sleep(10);            //sleep 10ms
                Thread.sleep(0,10000);        //sleep 10000ns,0.01ms
            }catch(InterruptedException e){
                e.printStackTrace();
            }
        };

        Thread tA = new Thread(r);
        long startTime = System.nanoTime();
        r.run();
        long endTime = System.nanoTime();
        long eclapsed = endTime -startTime;
        System.out.printf("elapsed time is %d",eclapsed);
    }
}