Chapter 11
Arrays Continued
Fundamentals of Java
Objectives
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Use string methods appropriately.
Write a method for searching an array.
Understand why a sorted array can be
searched more efficiently than an unsorted
array.
Write a method to sort an array.
Fundamentals of Java
Objectives (cont.)
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3
Write methods to perform insertions and
removals at given positions in an array.
Understand the issues involved when
working with arrays of objects.
Perform simple operations with Java’s
ArrayList class.
Fundamentals of Java
Vocabulary
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Array list
Binary search
Bubble sort
Immutable object
Insertion sort
Fundamentals of Java
Vocabulary (cont.)
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Linear search
Selection sort
Substring
Wrapper class
Fundamentals of Java
Advanced Operations on Strings
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Most text-processing applications examine
and manipulate the characters in strings.
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String objects are immutable.
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Separating strings into segments
Searching for/replacing specific characters or
substrings
Inserting text into a string
No mutators in the String class
Fundamentals of Java
Advanced Operations on
Strings (cont.)
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Table 11-1: Some commonly used String methods
Fundamentals of Java
Advanced Operations on
Strings (cont.)
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Table 11-1: Some commonly used String methods (cont.)
Fundamentals of Java
Advanced Operations on
Strings (cont.)
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Table 11-1: Some commonly used String methods (cont.)
Fundamentals of Java
Advanced Operations on
Strings (cont.)
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Example 11.2: Count the words and compute
the average word length in a sentence.
Fundamentals of Java
Advanced Operations on
Strings (cont.)
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Example 11.2: Count the words and compute the
average word length in a sentence (cont.).
Fundamentals of Java
Searching
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Linear search: Search a data structure (such
as an array) from beginning to end
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Searching an array of objects:
Fundamentals of Java
Searching (cont.)
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Binary search: An efficient search algorithm
based on eliminating half of the data from the
search at each iteration
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Data must be sorted first.
Examine midpoint of data, then decide which
half of the data to continue searching on.
 Discard
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other half of data.
Fundamentals of Java
Searching (cont.)
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Binary search code:
Fundamentals of Java
Searching (cont.)
Figure 11-1: Trace of a binary search of an array
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Fundamentals of Java
Searching (cont.)
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To compare objects, best if the class
implements the Comparable interface
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compareTo method
Table 11-2: Behavior of the method compareTo
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Fundamentals of Java
Searching (cont.)
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Binary search for objects:
Fundamentals of Java
Searching (cont.)
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Implementing a Comparable class example:
Fundamentals of Java
Sorting
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Arranging the elements of a collection of data
(such as an array) in an ordered fashion
Figure 11-2: Array before and after sorting
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Fundamentals of Java
Sorting: Selection Sort
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Basic idea:
Table 11-3: Trace of data during a selection sort
Fundamentals of Java
Sorting: Selection Sort (cont.)
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Must be able to find smallest number in an
array and swap items in an array
Fundamentals of Java
Sorting: Bubble Sort
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Pass through array comparing adjacent
elements
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If out of order, swap.
Table 11-4: Trace of data during one pass
of a bubble sort
Fundamentals of Java
Sorting: Bubble Sort (cont.)
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Pseudocode:
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Fewer data exchanges than selection sort
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Sort can stop early if array already sorted
Fundamentals of Java
Sorting: Insertion Sort
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After kth pass of sorting loop (k starting at 1),
first k items should be in sorted order.
Table 11-4: Trace of data during an insertion sort
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Fundamentals of Java
Sorting: Insertion Sort (cont.)
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Pseduocode:
Fundamentals of Java
Sorting (cont.)
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Any of the search algorithms can be altered
to support sorting of objects.
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Object’s class(es) should implement Comparable
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Have compareTo method
Example:
Fundamentals of Java
Insertions and Removals
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Steps for insertion:
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1. Check for available space.
2. Check validity of target index.
 Between
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0 and logical size
3. Shift items from logical end of array to target
index down by one position.
4. Assign new item to cell at target index.
5. Increment logical size by one.
Fundamentals of Java
Insertions and Removals (cont.)
Figure 11-3: Inserting an item into an array
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Fundamentals of Java
Insertions and Removals (cont.)
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Steps for removal:
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1. Check validity of target index.
 Between
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0 and logical size
2. Shift items from target index to logical end of
array up by one position.
3. Decrement logical size by one.
Fundamentals of Java
Insertions and Removals (cont.)
Figure 11-4: Removing an item from an array
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Fundamentals of Java
Working with Arrays of Objects
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When array type is an interface type, abstract
class, or superclass of 1+ other classes, array
may contain different object types.
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Might not all respond to common set of
messages
Fundamentals of Java
Working with Arrays of
Objects (cont.)
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What if you want to perform an operation
specific to one of the types in the array?
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Most general arrays have type Object.
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Can use the instanceOf operator to determine
the specific type of element in the array
Can hold any type of object
Fundamentals of Java
The Class java.util.ArrayList
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Contains sequence of elements ordered by
position
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Unlike an array in that:
It uses methods rather than [] to manipulate
elements.
 It tracks the logical size and physical size.
 The logical size is 0 when created.
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Size automatically adjusted as needed
The positions available for access range from 0 to
the logical size minus 1.
Fundamentals of Java
The Class java.util.ArrayList
(cont.)
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Generic array list: Programmer must specify
element type for the list
Raw array list: Can contain objects of any
reference type
Declaring/instantiating a generic array list:
Fundamentals of Java
The Class java.util.ArrayList
(cont.)
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Table 11-6: Some commonly used ArrayList methods
Fundamentals of Java
The Class java.util.ArrayList
(cont.)
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ArrayList objects cannot directly store
primitive types.
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Must use wrapper classes
 Classes
that contain the value of a primitive type
 Boolean, Integer, Double, Character
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Fundamentals of Java
The Class java.util.ArrayList
(cont.)
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ArrayList objects automatically “box” and
“unbox” primitive values when used with
ArrayList methods.
Fundamentals of Java
The Class java.util.ArrayList
(cont.)
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Advantages of ArrayList over arrays:
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Includes many methods for tasks such as
insertions, removals, and searches
Tracks own logical size and grows or shrinks
automatically with the number of elements
contained in it
Fundamentals of Java
Graphics and GUIs: Menus
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A drop-down menu system consists of a
menu bar, a number of menus, and several
selections for each menu.
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May have sub-menus
Menu item object for each menu selection
(class JMenuItem)
Menu object for each menu (class JMenu)
Menu bar object in which all of the menu
objects will appear (class JMenuBar)
Fundamentals of Java
Graphics and GUIs: Menus (cont.)
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Listener objects are attached to menus.
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When menu items are selected, events are fired
and the listener objects respond.
Figure 11-6: New user interface for the
student test scores program
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Fundamentals of Java
Graphics and GUIs: Menus (cont.)
Example 11.6: TestScoresView class (with menus)
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Fundamentals of Java
Graphics and GUIs: Menus (Cont.)
Example 11.6: TestScoresView class (with menus, cont.)
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Fundamentals of Java
Summary
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Linear search: Simple search that works
well for small- and medium-sized arrays
Binary search: Clever search that works
well for large arrays but assumes that the
elements are sorted
Comparisons of objects are accomplished by
implementing the Comparable interface,
which requires the compareTo method.
Fundamentals of Java
Summary (cont.)
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Selection sort, bubble sort, and insertion sort
are simple sort methods that work well for
small- and medium-sized arrays.
Insertions and removals of elements at
arbitrary positions are complex operations
that require careful design and
implementation.
Fundamentals of Java
Summary (cont.)
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One can insert objects of any class into an
array of Object. When retrieved from the
array, objects must be cast down to their
classes before sending them most
messages.
The limitation of a fixed-size array can be
overcome by using Java’s ArrayList class.
Fundamentals of Java
Summary (cont.)
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An array list tracks and updates its logical
size and provides many useful client
methods.
Wrapper class, such as Integer, provides a
way of packaging a value of a primitive type,
such as int, in an object so that it can be
stored in an array of Object or an array list.
Fundamentals of Java