Java Enums混乱

Question

我试图让我的头围绕枚举,一些代码行让我有些困惑.这可以直接从oracle docs站点获取,但在理解几行代码时遇到一些麻烦:

public class EnumTest {
    public enum Day {
        SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
        THURSDAY, FRIDAY, SATURDAY 
   }
    Day day;

    public EnumTest(Day day) {
    this.day = day;
    }

前5行(类EnumTest)非常好,真的很自我解释.我不明白的是上面代码的最后5行,令人困惑.有人可以在下面的完整代码的上下文中解释它们的含义吗？Enumtest(Day day)显然是一种方法,它的"this.day = day"和之前的"Day day"我没有得到.....

完整代码:

public class EnumTest {
    public enum Day {
        SUNDAY, MONDAY, TUESDAY, WEDNESDAY,
        THURSDAY, FRIDAY, SATURDAY 
    }
    Day day;

    public EnumTest(Day day) {
    this.day = day;
    }

    public void tellItLikeItIs() {
        switch (day) {
            case MONDAY:
                System.out.println("Mondays are bad.");
                break;

            case FRIDAY:
                System.out.println("Fridays are better.");
                break;

            case SATURDAY: case SUNDAY:
            System.out.println("Weekends are best.");
            break;

        default:
            System.out.println("Midweek days are so-so.");
            break;
        }
    }

    public static void main(String[] args) {
        EnumTest firstDay = new EnumTest(Day.MONDAY);
        firstDay.tellItLikeItIs();
        EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
        thirdDay.tellItLikeItIs();
        EnumTest fifthDay = new EnumTest(Day.FRIDAY);
        fifthDay.tellItLikeItIs();
        EnumTest sixthDay = new EnumTest(Day.SATURDAY);
        sixthDay.tellItLikeItIs();
        EnumTest seventhDay = new EnumTest(Day.SUNDAY);
        seventhDay.tellItLikeItIs();
    }
}

Answer 1

实际上,它并不像你认为的那样是一种方法.如果你注意到,有一个名为EnumTest的新类,那么你实际看到的是构造函数.然后它下面的行使用输入到构造函数中的this.day = day任何类对象实例设置日期EnumTest.可以在main方法中运行的示例代码是:

EnumTest fri = new EnumTest(Day.FRIDAY);

由于没有返回类型(即void或int等),您可以告诉它是构造函数.另一个线索是它具有相同的名称是持有它的类.