How to convert ArrayList to String[] in java, Arraylist contains VO objects

Question

Please help me to convert ArrayList to String[]. The ArrayList contains values of type Object(VO).

For example,

The problem is that I need to convert a country List to String Array, sort it and then put it in a list. However I am getting a ClassCastException.

Solution 1

String [] countriesArray = countryList.toArray(new String[countryList.size()]);

I have assumed that your country List name is countryList.

So to convert ArrayList of any class into array use following code. Convert T into the class whose arrays you want to create.

List<T> list = new ArrayList<T>();    
T [] countries = list.toArray(new T[list.size()]);

Solution 2

Please help me to convert ArrayList to String[], ArrayList Contains Values Object(VO) as Values.

As you mentioned that list contains Values Object i.e. your own class you need toString() overridden to make this work correctly.

This code works. Assuming VO is your Value Object class.

    List<VO> listOfValueObject = new ArrayList<VO>();
    listOfValueObject.add(new VO());
    String[] result = new String[listOfValueObject.size()];
    for (int i = 0; i < listOfValueObject.size(); i++) {
        result[i] = listOfValueObject.get(i).toString();
    }
    Arrays.sort(result);
    List<String> sortedList = Arrays.asList(result);

The snippet of

    List<VO> listOfValueObject = new ArrayList<VO>();
    listOfValueObject.add(new VO());
    String[] countriesArray = listOfValueObject.toArray(new String[listOfValueObject.size()]);

will give you ArrayStoreException due VO is not the String type as required by native method arraycopy subsequently called from toArray one.

Solution 3

In case your ArrayList contains Strings, you can simply use the toArray method:

String[] array = list.toArray( new String[list.size()] );

If that is not the case (as your question is not completely clear on this), you will have to manually loop over all elements

List<MyRandomObject> list;
String[] array = new String[list.size() ];
for( int i = 0; i < list.size(); i++ ){
  MyRandomObject listElement = list.get(i);
  array[i] = convertObjectToString( listElement );
}

Solution 4

String[] array = list.toArray(new String[list.size()]);

What are we doing here:

• String[] array is the String array you need to convert your ArrayList to
• list is your ArrayList of VO objects that you have in hand
• List#toArray(String[] object) is the method to convert List objects to Array objects

Solution 5

As correctly suggested by Viktor, I have edited my snippet.

The is a method in ArrayList(toArray) like:

List<VO> listOfValueObject // is your value object
String[] countries  = new String[listOfValueObject.size()];
for (int i = 0; i < listOfValueObject.size(); i++) {
    countries[i] = listOfValueObject.get(i).toString();
}

Then to sort you have::

Arrays.sort(countries);

Then re-converting to List like ::

List<String> countryList = Arrays.asList(countries);

View more solutions

Comments

[Viktor Stolbin]

toArray(new String[...]) will work only if list is of the same String type, won't it? Assuming the question the list is of type ValueObject.

[Viktor Stolbin]

This also will throw a ArrayStoreException.

[Viktor Stolbin]

And this will throw a ArrayStoreException too.

[Sashi Kant]

@ViktorStolbin: thanks of your suggestion, have edited my snippet, plz check

[Pramod Kumar]

It means that your are storing the wrong type of object into an array. You should reveal your code

[Viktor Stolbin]

It depends on what type the input list is :) I believe it is rather of type Value Object than the String type. You can see this in the question topic.

[user1000535]

Thank you very much, it helps me a lot to solve my problem, I got exact solution. the code is, List<CountryVO> countryList=new ArrayList<CountryVO>(); CountryVO vo=new CountryVO(); vo.setName("Malaisie"); countryList.add(vo); CountryVO vo1=new CountryVO(); vo1.setName("Allemagne"); countryList.add(vo1); String[] array = new String[countryList.size() ]; for( int i = 0; i < countryList.size(); i++ ){ CountryVO listElement = countryList.get(i); array[i]=listElement.getName(); }Arrays.sort(array); Thanks to All