how can i get last 7 days from current day in ascending order in java?

Question

I am using following code to get the last 7 days:

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd ");
Calendar cal = Calendar.getInstance();
Date date = cal.getTime();
String[] days = new String[6];
days[0] = sdf.format(date);

for(int i = 1; i < 6; i++){
    cal.add(Calendar.DAY_OF_MONTH, -1);
    date = cal.getTime();
    days[i] = sdf.format(date);
}

for(String x: days){
    System.out.println(x);
}

And this is giving the following output:

2016-04-14
2016-04-13
2016-04-12
2016-04-11
2016-04-10
2016-04-09

But I want this instead:

2016-04-09
2016-04-10
2016-04-11
2016-04-12
2016-04-13
2016-04-14

If I use the following line below the code it will give me the correct order:

List<String> list = Arrays.asList(days);
Collections.reverse(list);
days = (String[]) list.toArray();

for(String x: days){
    System.out.println(x);
}

But is there any other way to get the last 7 days in ascending order in one shot?

Answer 1

I would simplify your method a bit, if you want this output you don't need to create an String[] array, either loop twice, you can achieve same with a single for-loop, one Calendar and the SimpleDateFormat

SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd ");
Calendar cal = Calendar.getInstance();
// get starting date
cal.add(Calendar.DAY_OF_YEAR, -6);

// loop adding one day in each iteration
for(int i = 0; i< 6; i++){
    cal.add(Calendar.DAY_OF_YEAR, 1);
    System.out.println(sdf.format(cal.getTime()));
}

OUTPUT:

2016-04-09 
2016-04-10 
2016-04-11 
2016-04-12 
2016-04-13 
2016-04-14 

Working IDEONE demo

Answer 2

Using java8 and joda you can write something like:

LocalDate weekBeforeToday = LocalDate.now().minusDays(7);
IntStream.rangeClosed(1, 7)
    .mapToObj(weekBeforeToday::plusDays)
    .forEach(System.out::println);

It prints:

2016-04-08
2016-04-09
2016-04-10
2016-04-11
2016-04-12
2016-04-13
2016-04-14

If you need collection you have to use collector.

In your example you're printing 6 days so I don't now if it's your mistake or you need 6 days instead of 7.