我是一名初学者，对Java有一些经验。
我做了这个简单的日历程序，并在过去的一周里不断地修改。我想这样做，当用户输入一个月和一年时，会出现一系列完美的日期。但是，我想更改它，这样用户只需要一年，并且显示了整组月份。
例如，代码要求输入年份：。用户必须选择他们想要的任何年份（我已经处理了闰年问题），从1月到12月的所有月份都必须以正确的顺序显示。我试图修改我的代码，但我一直搞砸。我如何才能以最好的方式更改代码，以便在用户给出的一年中获得整个月数？

import java.util.Scanner;

public class Month
{
    private static final String[] MONTHS = {
            "", "January", "February", "March", "April", "May", "June", "July",
            "August", "September", "October", "November", "December"
        };

    private static final int[] NUMDAYS = {
            0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31
        };

    private int month;
    private int year;

    public Month(int month, int year) {
        this.month = month;
        this.year = year;
    }

    public int getMonth() {
        return month;
    }

    public int getYear() {
        return year;
    }

    private boolean isLeapYear() {
        if(year % 400 == 0) {
            return true;
        }
        if(year % 100 == 0) {
            return false;
        }
        return year % 4 == 0;
    }

    private int getNumDays() {
        if(month == 2) {
            if(isLeapYear()) {
                return 29;
            }
            else {
                return 28;
            }
        }
        else {
            return NUMDAYS[month];
        }
    }

    private int getStartDOW() {
        int m, y;
        if(month < 3) {
            m = month + 12;
            y = year - 1;
        }
        else {
            m = month;
            y = year;
        }
        return (13 * (m + 1) / 5 + y + y / 4 - y / 100 + y / 400) % 7;
    }

    public void printCalendar() {
        //I changed this part so that the month and year could be centered, if you have an 
        //easier or cleaner way to do it, I would appreciate learning it.

        if(month == 2||month == 11 || month == 12 || month == 9){
            System.out.println("    " + MONTHS[month] + " " + year);
        }else if(month == 3||month == 4 || month == 6 || month == 7 || month == 5){
            System.out.println("      " + MONTHS[month] + " " + year);
        }else if(month == 1||month == 10 || month == 8){

            //This is what I originally had System.out.println("    " + MONTHS[month] + " " 
            //+ year);
        }
        System.out.println(" S  M  T  W  T  F  S");
        int dow = getStartDOW();
        for(int i = 0; i < dow; i++) {
            System.out.print("   ");
        }
        int numdays = getNumDays();
        for(int i = 1; i <= numdays; i++) {
            System.out.printf("%2d ", i);
            if(dow == 6) {
                System.out.println();
                dow = 0;
            }
            else {
                dow++;
            }
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("Enter month (1-12)");
        int month = s.nextInt();
        System.out.println("Enter year: ");
        int year = s.nextInt();
        Month m = new Month(month, year);
        m.printCalendar();
    }
}