Java Calendar Diferença entre DATE e DAY_OF_MONTH

Olá Felipe, como vai?

ao que me parece são a mesma coisa... veja a documentação:

Calendar.DATE:

Field number for get and set indicating the day of the month. This is a synonym for DAY_OF_MONTH. The first day of the month has value 1. See Also: DAY_OF_MONTH < 1.8 >

Calendar.DAY_OF_MONTH:

Field number for get and set indicating the day of the month. This is a synonym for DATE. The first day of the month has value 1. See Also: DATE < 1.8 >

Executando o código abaixo teremos os mesmos valores:

import java.util.Calendar;

public class TesteCalendarJava {

    public static void main(String[] args) {

        // create a calendar
        Calendar cal = Calendar.getInstance();

    int a1 = cal.getActualMaximum(Calendar.DAY_OF_MONTH);
        System.out.println("ActualMaximum day DAY_OF_MONTH:" + a1);

        int date = cal.getActualMaximum(Calendar.DATE);
        System.out.println("ActualMaximum day DATE:" + date);
    }
}