为什么字节参数不能识别为整数？

Question

I have the following enum:

public enum Months {
    JAN(31),
    FEB(28),
    MAR(31),
    APR(30),
    MAY(31),
    JUN(30),
    JUL(31),
    AUG(31),
    SEP(30),
    OCT(31),
    NOV(30),
    DEC(31);

    private final byte DAYS; //days in the month

    private Months(byte numberOfDays){
        this.DAYS = numberOfDays;
    }//end constructor

    public byte getDays(){
        return this.Days;
    }//end method getDays
}//end enum Months

It gives me an error that says "The constructor Months(int) is undefined" although I am passing a valid byte arguments. What am I doing wrong?

Answer 1

The simplest solution is to accept an int value

private Months(int numberOfDays){
    this.DAYS = (byte) numberOfDays;
}

BTW non-static fields should be in camelCase not UPPER_CASE

Also FEB has 29 days in some years.

public static boolean isLeapYear(int year) {
    // assume Gregorian calendar for all time
    return year % 4 == 0 && (year % 100 != 0 || year % 400 == 0);
}

public int getDays(int year) {
    return days + (this == FEB && isLeapYear(year) ? 1 : 0);
} 

Answer 2

Those numbers are int literals. You'd have to cast them to byte :

 JAN((byte)31),

Answer 3

The Java Language Specification says the following regarding lexical integer literals:

The type of a literal is determined as follows:

• The type of an integer literal (§3.10.1) that ends with L or l is long (§4.2.1).
• The type of any other integer literal is int (§4.2.1).

So it requires you to explicitly cast this integer literal to byte.