Java ArrayList and HashMap on-the-fly

Question

Can someone please provide an example of creating a Java ArrayList and HashMap on the fly? So instead of doing an add() or put(), actually supplying the seed data for the array/hash at the class instantiation?

To provide an example, something similar to PHP for instance:

$array = array (3, 1, 2); $assoc_array = array( 'key' => 'value' ); 

Answer 1

List<String> list = new ArrayList<String>() {  {     add("value1");     add("value2");  } };  Map<String,String> map = new HashMap<String,String>() {  {     put("key1", "value1");     put("key2", "value2");  } }; 

Answer 2

A nice way of doing this is using List.of() and Map.of() (since Java 8):

List<String> list = List.of("A", "B", "C");      Map<Integer, String> map = Map.of(1, "A",                                   2, "B",                                   3, "C"); 

Java 7 and earlier may use Google Collections:

List<String> list = ImmutableList.of("A", "B", "C");  Map<Integer, String> map = ImmutableMap.of(   1, "A",   2, "B",   3, "C");