Data Structures and Algorithms in Java[1].pdf - Fulvio Frisone

Moreover, the java.util.ArrayList class has features in addition to those
of our simplified array list ADT. For example, the class
java.util.ArrayList also includes a method, clear(), which removes
all the elements from the array list, and a method, toArray(), which returns an
array containing all the elements of the array list in the same order. In addition,
the class java.util.ArrayList also has methods for searching the list,
including a method indexOf(e), which returns the index of the first occurrence
of an element equal to e in the array list, and a method lastIndexOf(e),
which returns the index of the last occurrence of an element equal to e in the array
list. Both of these methods return the (invalid) index value − 1 if an element equal
to e is not found.
6.1.5 Implementing an Array List Using Extendable
Arrays
In addition to implementing the methods of the IndexList interface (and some
other useful methods), the class java.util.ArrayList provides an an
interesting feature that overcomes a weakness in the simple array implementation.
Specifically, a major weakness of the simple array implementation for the array list
ADT given in Section 6.1.3, is that it requires advance specification of a fixed
capacity, N, for the total number of elements that may be stored in the array list. If
the actual number of elements, n, of the array list is much smaller than N, then this
implementation will waste space. Worse, if n increases past N, then this
implementation will crash.
Instead, the java.util.ArrayList uses an interesting extendable-array
technique so that we never have to worry about array overflows when using this
class.
As with the java.util.ArrayList class, let us provide a means to grow the
array A that stores the elements of an array list S. Of course, in Java (and other
programming languages), we cannot actually grow the array A; its capacity is fixed
at some number N, as we have already observed. Instead, when an overflow occurs,
that is, when n = N and we make a call to the method add, we perform the
following additional steps:
1. Allocate a new array B of capacity 2N
2. Let B[i ]← A[i], for i = 0,... , N − 1
3. Let A ← B, that is, we use B as the array supporting S
4. Insert the new element in A.
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