Abstract class with final uninitialized field

Question

I was wondering if the below code makes any sense, since the compiler warns that "the blank final field objects may not have been initialized". Is there a better way of doing this?

public abstract Test {   protected final ArrayList<Object> objects; }  public TestSubA extends Test {    public TestSubA() {     objects = new ArrayList<Objects>(20);     // Other stuff   } }  public TestSubB extends Test {    public TestSubB() {     objects = new ArrayList<Objects>(100);     // Other stuff   } } 

Answer 1

I would make the field final and force the constructors to pass the value up:

public abstract class Test {   private final ArrayList<Object> objects;    protected ArrayList<Object> getObjects() {     return objects;   }    protected Test(ArrayList<Object> objects) {     this.objects = objects;   } }  public class TestSubA extends Test {    public TestSubA() {     super(new ArrayList<Object>(20));     // Other stuff   } }  public class TestSubB extends Test {    public TestSubB() {     super(new ArrayList<Object>(100));     // Other stuff   } } 

Answer 2

The problem with initializing the final parameters directly in the constructor of the sub-classes is that you need to do it all in one line since super() must be the first statement of the constructor. So instead, I prefer to make the constructor non-public and make a static build method like this:

public abstract class Test {   protected final ArrayList<Object> objects;    protected Test(ArrayList<Object> objects) {     this.objects = objects;   } }  public class TestSubA extends Test {   public static TestSubA build() {     ArrayList<Object> objects = new ArrayList<Object>(20);     objects.put(...);     // Other stuff     return new TestSubA(objects);   }    private TestSubA(ArrayList<Object> objects) {     super(objects);   } }