The problem

Using the result of an assignment expression can be quite unclear, except for simple cases where the result is used to initialise another variable, such as x = y = 0.

Consider a common pattern of lazily initialising a field:

class Lazy<T> {
  private T t = null;

  abstract T create();

  public T get() {
    if (t != null) {
      return t;
    }
    return t = create();
  }
}

class Lazy<T> {
  private T t = null;

  abstract T create();

  public T get() {
    if (t != null) {
      return t;
    }
    t = create();
    return t;
  }
}

At the cost of another line, it’s now clearer what’s happening. (Note that neither the before nor the after are thread-safe; this particular example would be better served with Suppliers.memoizing.)

Suppression

Suppress false positives by adding the suppression annotation @SuppressWarnings("AssignmentExpression") to the enclosing element.