关于java中AbstractList的hashCode function的问题

Question

At line 540, why could we use this pointer of AbstractList in foreach?

538. public int hashCode() {
539.     int hashCode = 1;
540.     for (E e : this)
541.         hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
542.     return hashCode;
543. }

Screenshot

Answer 1

It iterates over the list items and create a hash code depended for that. For every item you add or remove from list changes hashcode. This is the default implementation to create uniqueness for a list.

Answer 2

The question can be divided in two parts:

---

"why could we use this pointer of AbstractList"

this always returns the actual instance; it is also valid in an abstract class, being similar, in that case, to a parameter defined as AbstractList this initialized with the actual instance. Like in:

public int hashCode(AbstractList this) {
    ...
}

See JLS 15.8.3. this for more details.

---

"why could we use... AbstractList in foreach"

the AbstractList can be used in the enhanced for loop because it implements the Iterable interface. See documentation JLS 14.14.2. The enhanced for statement :

The type of the Expression must be a subtype of the raw type Iterable or an array type

and of Iterable :

Implementing this interface allows an object to be the target of the enhanced for statement (sometimes called the "for-each loop" statement).