Java泛型擦除有点懵

Question

public class FX1 {
    public static void main(String[] args) {
        Map<DayOfWeek, String> map = new EnumMap<>(DayOfWeek.class);
        map.put(DayOfWeek.MONDAY, "星期一");
        map.put(DayOfWeek.TUESDAY, "星期二");
        map.put(DayOfWeek.WEDNESDAY, "星期三");
        map.put(DayOfWeek.THURSDAY, "星期四");
        map.put(DayOfWeek.FRIDAY, "星期五");
        map.put(DayOfWeek.SATURDAY, "星期六");
        map.put(DayOfWeek.SUNDAY, "星期日");
        System.out.println(map);
        System.out.println(map.get(DayOfWeek.MONDAY));
    }
}

public class FX2 {
    public static void main(String[] args) {
        Map<String, Integer> map = new TreeMap<>();
        map.put("orange", 1);
        map.put("apple", 2);
        map.put("pear", 3);
        for (String key : map.keySet()) {
            System.out.println(key);
        }
    }
}

为什么第一个类中实例化必须要传入DayOfWeek.class，而第二个类中实例不传任何参数，传入了反而报错。求各位大佬解答

Answer 1

这个跟泛型擦除没有关系 , TreeMap没有参数为Class的构造方法 , 你传入Class当然会报错