Generic Collections - Java: How to Program Early Objects - page 696

identically to method add (line 15). Line 17 calls LinkedList method addFirst to add
"cyan" as the new first item in the LinkedList . The add operations are permitted because
they operate on the LinkedList object, not the view returned by asList . [ Note: When
"cyan" is added as the first element, "green" becomes the fifth element in the
LinkedList .]
Line 20 calls the List interface's toArray method to get a String array from links . The
array is a copy of the list's elements—modifying the array's contents does not modify the list.
The array passed to method toArray is of the same type that you'd like method toArray to
return. If the number of elements in that array is greater than or equal to the number of ele-
ments in the LinkedList , toArray copies the list's elements into its array argument and
returns that array. If the LinkedList has more elements than the number of elements in the
array passed to toArray , toArray allocates a new array of the same type it receives as an argu-
ment, copies the list's elements into the new array and returns the new array.

Common Programming Error 16.2
Passing an array that contains data to toArray can cause logic errors. If the number of
elements in the array is smaller than the number of elements in the list on which toArray
is called, a new array is allocated to store the list's elements— without preserving the ar-
ray argument's elements . If the number of elements in the array is greater than the num-
ber of elements in the list, the elements of the array (starting at index zero) are overwritten
with the list's elements. Array elements that are not overwritten retain their values.

16.7 Collections Methods
Class Collections provides several high-performance algorithms for manipulating collec-
tion elements. The algorithms (Fig. 16.5) are implemented as static methods. The meth-
ods sort , binarySearch , reverse , shuffle , fill and copy operate on List s. Methods
min , max , addAll , frequency and disjoint operate on Collection s.

Method Description

Sorts the elements of a List .

sort

Locates an object in a List , using the high-performance binary search algorithm
which we introduced in Section 7.15 and discuss in detail in Section 19.4.

binarySearch

Reverses the elements of a List .

reverse

Randomly orders a List 's elements.

shuffle

Sets every List element to refer to a specified object.

fill

Copies references from one List into another.

copy

Returns the smallest element in a Collection .

min

Returns the largest element in a Collection .

max

Appends all elements in an array to a Collection .

addAll

Calculates how many collection elements are equal to the specified element.

frequency

Determines whether two collections have no elements in common.

disjoint

Fig. 16.5 | Collections methods.