Initializing ArrayList with some predefined values [duplicate]

Answer 1

Personnaly I like to do all the initialisations in the constructor

public Test()
{
  symbolsPresent = new ArrayList<String>();
  symbolsPresent.add("ONE");
  symbolsPresent.add("TWO");
  symbolsPresent.add("THREE");
  symbolsPresent.add("FOUR");
}

Edit : It is a choice of course and others prefer to initialize in the declaration. Both are valid, I have choosen the constructor because all type of initialitions are possible there (if you need a loop or parameters, ...). However I initialize the constants in the declaration on the top on the source.
The most important is to follow a rule that you like and be consistent in our classes.

Answer 2

Java 9 allows you to create an unmodifiable list with a single line of code using List.of factory:

public class Main {
    public static void main(String[] args) {
        List<String> examples = List.of("one", "two", "three");
        System.out.println(examples);
    }
}

Output:

[one, two, three]

Answer 3

I would suggest to use Arrays.asList() for single line initialization. For different ways of declaring and initializing a List you can also refer Initialization of ArrayList in Java

Answer 4

How about using overloaded ArrayList constructor.

 private ArrayList<String> symbolsPresent = new ArrayList<String>(Arrays.asList(new String[] {"One","Two","Three","Four"}));

Answer 5

Also, if you want to enforce the List to be read-only (throws a UnsupportedOperationException if modified):

List<String> places = Collections.unmodifiableList(Arrays.asList("One", "Two", "Three"));

Answer 6

import com.google.common.collect.Lists;

...


ArrayList<String> getSymbolsPresent = Lists.newArrayList("item 1", "item 2");

...