最终未初始化字段的抽象类

Question

我想知道下面的代码是否有意义,因为编译器警告"空白的最终字段对象可能尚未初始化".有没有更好的方法呢？

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

我会使字段最终并强制构造函数传递值:

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

直接在子类的构造函数中初始化最终参数的问题是,您需要在一行中完成所有操作,因为super()必须是构造函数的第一个语句.所以相反,我更喜欢使构造函数非公共,并创建一个这样的静态构建方法:

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);
  }
}