How to add new elements to an array?
The size of an array can't be modified. If you want a bigger array you have to instantiate a new one.
A better solution would be to use an ArrayList
which can grow as you need it. The method ArrayList.toArray( T[] a )
gives you back your array if you need it in this form.
List<String> where = new ArrayList<String>();
where.add( ContactsContract.Contacts.HAS_PHONE_NUMBER+"=1" );
where.add( ContactsContract.Contacts.IN_VISIBLE_GROUP+"=1" );
If you need to convert it to a simple array...
String[] simpleArray = new String[ where.size() ];
where.toArray( simpleArray );
But most things you do with an array you can do with this ArrayList, too:
// iterate over the array
for( String oneItem : where ) {
...
}
// get specific items
where.get( 1 );
Use a List<String>
, such as an ArrayList<String>
. It's dynamically growable, unlike arrays (see: Effective Java 2nd Edition, Item 25: Prefer lists to arrays).
import java.util.*;
//....
List<String> list = new ArrayList<String>();
list.add("1");
list.add("2");
list.add("3");
System.out.println(list); // prints "[1, 2, 3]"
If you insist on using arrays, you can use java.util.Arrays.copyOf
to allocate a bigger array to accomodate the additional element. This is really not the best solution, though.
static <T> T[] append(T[] arr, T element) {
final int N = arr.length;
arr = Arrays.copyOf(arr, N + 1);
arr[N] = element;
return arr;
}
String[] arr = { "1", "2", "3" };
System.out.println(Arrays.toString(arr)); // prints "[1, 2, 3]"
arr = append(arr, "4");
System.out.println(Arrays.toString(arr)); // prints "[1, 2, 3, 4]"
This is O(N)
per append
. ArrayList
, on the other hand, has O(1)
amortized cost per operation.
See also
- Java Tutorials/Arrays
- An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed.
- Java Tutorials/The List interface