java计算30天后日期

import java.util.Scanner;
public class Work2 {
    public static void main(String []args){
        Scanner in = new Scanner(System.in);
        int year = in.nextInt();
        int month = in.nextInt();
        int day = in.nextInt();
        int left = 0;
        boolean leap;

        if( (year%4==0 && year%100!=0) || year%400==0){
            leap = true;
        }
        switch(month){
            case 1: case 3: case 5: case 7: case 8: case 10:
                left = 31 - day;
                if (left<30) {
                    month++;
                    day = left;
                }
                else
                    day = 31;//输入为1号的特殊情况
                break;
            case 4: case 6: case 9: case 11:
                left = 30 - day;
                month ++;
                day = left;
                break;
            case 12:
                left = 31 - day;
                if(left<30){
                    month++;
                    year++;
                    day = left;
                }
                else
                    day = 31;
                break;
            case 2:
                if(leap = true){
                    left = 29- day;
                    month = 3;
                    day = left;
                }
                else{
                    left = 28 - day;
                    month ++;
                    day = left;
                }
                break;
        }
        System.out.println("该日期30天后的日期是："+year+" "+month+" "+day);
    }
}

         /*
         先给定一个时间，例如2017年10月1日
         */
         Calendar cld = Calendar.getInstance();
         cld.set(Calendar.YEAR, 2017);
         cld.set(Calendar.MONDAY,10);
         cld.set(Calendar.DATE,1);
          
        //调用Calendar类中的add()，增加时间量
       cld.add(Calendar.DATE, 30);
         System.out.println(year+"年"+month+"月"+date+"日");