你能简化这个 if 语句吗？

Question

I am looking to somehow simplify the following: monthNbr==11||monthNbr==4||monthNbr==6||monthNbr==9 here:

public int daysPerMonth (int monthNbr){
    if(monthNbr==11||monthNbr==4||monthNbr==6||monthNbr==9){
        return 30;
    } else if (monthNbr==2) {
        return 28;
    } else {
        return 31;
    }
}

Answer 1

perhaps it would look nicer with the new switch expressions

public int daysPerMonth(int monthNbr) {
    return switch (monthNbr) {
        case 11, 4, 6, 9 -> 30;
        case 2 -> 28;
        default -> 31;
    };
}

Answer 2

Don't reinvent the wheel:

Month.of(monthNbr).length(isLeapYear)

Answer 3

Since Java 8, you can also do:

public int daysPerMonth(int monthNbr) {
    return YearMonth.of(Year.now().getValue(),monthNbr).lengthOfMonth();
}

and this will get you the number of the months for the current year.

Also, note, that Switch Expressions can be only used since Java 12.

Answer 4

Here is one smaller version, it should also be easy to extend to support leap years. Either by send the year or send year 2000 if you want leap year.

import java.util.*; 
import java.time.*;

public class HelloDays
{
     public static int daysPerMonth(int monthNbr)
     {
        YearMonth yearMonthObject = YearMonth.of(1999, monthNbr);
        return yearMonthObject.lengthOfMonth();  
     }
     
     public static void main(String []args)
     {
        System.out.println(daysPerMonth(1));  // 31
        System.out.println(daysPerMonth(2));  // 28
        System.out.println(daysPerMonth(4));  // 30
        
     }
}

Answer 5

You can use stream like this.

public int daysPerMonth(int monthNbr) {
    if (IntStream.of(11, 4, 6, 9).anyMatch(i -> monthNbr == i)) {
        return 30;
    } else if (monthNbr == 2) {
        return 28;
    } else {
        return 31;
    }
}