第一个元素在java.util.List中被覆盖

Question

I have a list converted to a String array. At index 0 of the array, I have assigned the String "Select a value" . Now when I am iterating over the String array, the first element is overridden by the value I have assigned as "Select a value".

Below is the code:

List<LocalDate> localDatesList = new ArrayList<LocalDate>();
localDatesList.add(new LocalDate());
localDatesList.add(new LocalDate().plusDays(1));
localDatesList.add(new LocalDate().plusDays(2));
localDatesList.add(new LocalDate().plusMonths(1));
localDatesList.add(new LocalDate().plusMonths(2));
List<String> tempDatesList = new ArrayList(localDatesList.size());
for (LocalDate date : localDatesList) {
    tempDatesList.add(date.toString());  
}
String[] formattedDates = tempDatesList.toArray(new String[localDatesList.size()]);
formattedDates[0]="Select a value";
for (String dates : formattedDates) {
    System.out.println(dates);
}

Output:

2016-10-14
2016-10-15
2016-11-13
2016-12-13

I tried to increase the size by 1, but null is added at the last index, and it's not showing the current date (first element I have added in the list).

Please suggest what I am missing, how can I add the value "Select a Value" at index zero or first element in the list. The first element is missing in the list when I added formattedDates[0]="Select a value" .

Answer 1

You are overriding your fist element in this line:

formattedDates[0]="Select a value";

change your code like this and add the "Select a Value" before your loop:

List<LocalDate> localDatesList = new ArrayList<LocalDate>();
localDatesList.add(new LocalDate());
localDatesList.add(new LocalDate().plusDays(1));
localDatesList.add(new LocalDate().plusDays(2));
localDatesList.add(new LocalDate().plusMonths(1));
localDatesList.add(new LocalDate().plusMonths(2));

List<String> tempDatesList = new ArrayList(localDatesList.size());
tempDatesList.add("Select a value");
for (LocalDate date : localDatesList) {
    tempDatesList.add(date.toString());
}

String[] formattedDates = tempDatesList.toArray(new String[localDatesList.size()]);
for (String dates : formattedDates) {
    System.out.println(dates);
}

Answer 2

You are overriding first element by your own. You can't increase the size of array, whatever you will assign for a particular position that will be updated with that value.If you change it will change for that particular position.

In your code you are assigning 0 position with select a value( formattedDates[0]="Select a value"; ).

So before changing list to array, add "Select a value" to list and then convert.Then it will work fine.

tempDatesList.add("Select a value");

then add dates

for (LocalDate date : localDatesList) {
    tempDatesList.add(date.toString());  
}

and then

tempDatesList.toArray(new String[localDatesList.size()]);

Here is the refined code:

List<String> localDatesList = new ArrayList<String>();
localDatesList.add(LocalDate.now().toString());
localDatesList.add(LocalDate.now().plusDays(1).toString());
localDatesList.add(LocalDate.now().plusDays(2).toString());
localDatesList.add(LocalDate.now().plusMonths(1).toString());
localDatesList.add(LocalDate.now().plusMonths(2).toString());
localDatesList.add("Select a value");
String[] formattedDates = localDatesList.toArray(new String[localDatesList.size()]);
for (String dates : formattedDates) {
    System.out.println(dates);
}

Answer 3

When you put the value "Select a value" you change the array's first value. You can do something like this:

String[] formattedDates = new String[localDatesList.size() + 1];
formattedDates[0]="Select a value";
System.arraycopy(tempDatesList.toArray(), 0, formattedDates, 1, tempDatesList.toArray().length);

Answer 4

I have modified the code for you.

public static void main(final String arhgsp[]) {
    final List<LocalDate> localDatesList = new ArrayList<>();
    localDatesList.add(LocalDate.now());
    localDatesList.add(LocalDate.now().plusDays(1));
    localDatesList.add(LocalDate.now().plusDays(2));
    localDatesList.add(LocalDate.now().plusMonths(1));
    localDatesList.add(LocalDate.now().plusMonths(2));
    final List<String> tempDatesList = new ArrayList<>(localDatesList.size());
    for (final LocalDate date : localDatesList) {
        tempDatesList.add(date.toString());
    }
    final String[] formattedDates = tempDatesList.toArray(new String[localDatesList.size()]);
    formattedDates[0] = "Select a value";
    for (final String dates : formattedDates) {
        System.out.println(dates);
    }
}

produced the output

Select a value
2016-10-14
2016-10-15
2016-11-13
2016-12-13

Hope this would work for you.