Initializing ArrayList with some predefined values [duplicate]

Answer 1

public static final List<String> permissions = new ArrayList<String>() {{
    add("public_profile");
    add("email");
    add("user_birthday");
    add("user_about_me");
    add("user_location");
    add("user_likes");
    add("user_posts");
}};

Answer 2

I use a generic class that inherit from ArrayList and implement a constructor with a parameter with variable number or arguments :

public class MyArrayList<T> extends ArrayList<T> {
    public MyArrayList(T...items){
        for (T item : items) {
            this.add(item);
        }
    }
}

Example:

MyArrayList<String>myArrayList=new MyArrayList<String>("s1","s2","s2");

Answer 3

try this

new String[] {"One","Two","Three","Four"};

or

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

ARRAYS

Answer 4

If you just want to initialize outside of any method then use the initializer blocks :

import java.util.ArrayList;

public class Test {
private ArrayList<String> symbolsPresent = new ArrayList<String>();

// All you need is this block.
{
symbolsPresent = new ArrayList<String>();
symbolsPresent.add("ONE");
symbolsPresent.add("TWO");
symbolsPresent.add("THREE");
symbolsPresent.add("FOUR");
}


public ArrayList<String> getSymbolsPresent() {
    return symbolsPresent;
}

public void setSymbolsPresent(ArrayList<String> symbolsPresent) {
    this.symbolsPresent = symbolsPresent;
}

public static void main(String args[]) {    
    Test t = new Test();
    System.out.println("Symbols Present is" + t.symbolsPresent);

}    
}

Answer 5

You can also use the varargs syntax to make your code cleaner:

Use the overloaded constructor:

ArrayList<String> list = new ArrayList<String>(Arrays.asList("a", "b", "c"));

Subclass ArrayList in a utils module:

public class MyArrayList<T> extends ArrayList<T> {
    public MyArrayList(T... values) {
        super(Arrays.asList(values));
    }
}

ArrayList<String> list = new MyArrayList<String>("a", "b", "c");

Or have a static factory method (my preferred approach):

public class Utils {
  public static <T> ArrayList<T> asArrayList(T... values) {
    return new ArrayList<T>(Arrays.asList(values));
  }
}

ArrayList<String> list = Utils.asArrayList("a", "b", "c");

Answer 6

You can use Java 8 Stream API.
You can create a Stream of objects and collect them as a List.

private List<String> symbolsPresent = Stream.of("ONE", "TWO", "THREE", "FOUR")
    .collect(Collectors.toList());