Valid date format check in Java

When I execute the below code I get a ‘True’ even though the date which I supply is incorrect (2010-55-04). Could someone please clarify why that is the case.

package basic;

import java.text.ParseException;
import java.text.SimpleDateFormat;

public class VerifyIfStrngIsValidDate {

    public static boolean checkdate(String dt1)
    {
        SimpleDateFormat df1=new SimpleDateFormat("yyyy-mm-dd");
        System.out.println(df1.toPattern());
        df1.setLenient(false);
        try {
            df1.parse(dt1);
        } catch (ParseException e) {

            return false;
        }
        return true;
    }

    public static void main(String[] args) {

        boolean res;
        res=checkdate("2010-55-04");
        System.out.println(res);
    }

}