Inner classes and implementation of ArrayList - Data Structures and Problem Solving Using Java - page 593

1 public void clear( ) // Version #1
2 {
3 Iterator<AnyType> itr = iterator( );
4

figure 15.18
Proposed
implementations of
clear for
AbstractCollection

while( !isEmpty( ) )

remove( itr.next( ) ); 5

6 }
7
8 public void clear( ) // Version #2
9 {
10 while( !isEmpty( ) )

remove( iterator( ).next( ) ); 11

12 }

Figure 15.18 contains two proposed implementations of clear for
AbstractCollection . Does either work?

15.10

PROGRAMMING PROJECTS
15.11 The Collection interface in the Java Collections API defines methods
removeAll , addAll , and containsAll . Add these methods to the Collection
interface and provide implementations in AbstractCollection .
15.12 Collections.unmodifiableCollection takes a Collection and returns an
immutable Collection . Implement this method. To do so, you will need
to use a local class (a class inside a method). The class implements the
Collection interface and throws an UnsupportedOperationException for
all mutating methods. For other methods, it forwards the request to the
Collection being wrapped. You will also have to hide an unmodifiable
iterator.

Two Collection objects are equal if either both implement the List inter-
face and contain the same items in the same order or both implement the
Set interface and contain the same items in any order. Otherwise, the
Collection objects are not equal. Provide, in AbstractCollection , an
implementation of equals that follows this general contract. Addition-
ally, provide a hashCode method in AbstractCollection that follows the
general contract of hashCode . (Do this by using an iterator and adding the
hashCode s of all the entries. Watch out for null entries.)

15.13