This document discusses advanced operations on arrays in Java, including searching, sorting, insertions, and removals. It covers linear and binary search algorithms, selection, bubble, and insertion sort methods, and how to implement searches and sorts for arrays of objects. It also introduces the ArrayList class in Java and how it provides a more flexible alternative to arrays.

1. Chapter 11
Arrays Continued
Fundamentals of Java

2. Fundamentals of Java
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Objectives
 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.

3. Fundamentals of Java
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Objectives (cont.)
 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.

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Vocabulary
 Array list
 Binary search
 Bubble sort
 Immutable object
 Insertion sort

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Vocabulary (cont.)
 Linear search
 Selection sort
 Substring
 Wrapper class

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Advanced Operations on Strings
 Most text-processing applications examine
and manipulate the characters in strings.
– Separating strings into segments
– Searching for/replacing specific characters or
substrings
– Inserting text into a string
 String objects are immutable.
– No mutators in the String class

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Advanced Operations on
Strings (cont.)
Table 11-1: Some commonly used String methods

8. Fundamentals of Java
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Advanced Operations on
Strings (cont.)
Table 11-1: Some commonly used String methods (cont.)

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Advanced Operations on
Strings (cont.)
Table 11-1: Some commonly used String methods (cont.)

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Advanced Operations on
Strings (cont.)
Example 11.2: Count the words and compute
the average word length in a sentence.

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Advanced Operations on
Strings (cont.)
Example 11.2: Count the words and compute the
average word length in a sentence (cont.).

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Searching
 Linear search: Search a data structure (such
as an array) from beginning to end
 Searching an array of objects:

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Searching (cont.)
 Binary search: An efficient search algorithm
based on eliminating half of the data from the
search at each iteration
– Data must be sorted first.
– Examine midpoint of data, then decide which
half of the data to continue searching on.
 Discard other half of data.

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Searching (cont.)
 Binary search code:

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Searching (cont.)
Figure 11-1: Trace of a binary search of an array

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Searching (cont.)
 To compare objects, best if the class
implements the Comparable interface
– compareTo method
Table 11-2: Behavior of the method compareTo

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Searching (cont.)
 Binary search for objects:

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Searching (cont.)
 Implementing a Comparable class example:

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Sorting
 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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Sorting: Selection Sort
 Basic idea:
Table 11-3: Trace of data during a selection sort

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Sorting: Selection Sort (cont.)
 Must be able to find smallest number in an
array and swap items in an array

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Sorting: Bubble Sort
 Pass through array comparing adjacent
elements
– If out of order, swap.
Table 11-4: Trace of data during one pass
of a bubble sort

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Sorting: Bubble Sort (cont.)
 Pseudocode:
 Fewer data exchanges than selection sort
– Sort can stop early if array already sorted

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Sorting: Insertion Sort
 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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Sorting: Insertion Sort (cont.)
 Pseduocode:

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Sorting (cont.)
 Any of the search algorithms can be altered
to support sorting of objects.
– Object’s class(es) should implement Comparable
 Have compareTo method
 Example:

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Insertions and Removals
 Steps for insertion:
– 1. Check for available space.
– 2. Check validity of target index.
 Between 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.

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Insertions and Removals (cont.)
Figure 11-3: Inserting an item into an array

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Insertions and Removals (cont.)
 Steps for removal:
– 1. Check validity of target index.
 Between 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.

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Insertions and Removals (cont.)
Figure 11-4: Removing an item from an array

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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.
– Might not all respond to common set of
messages
Working with Arrays of Objects

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Working with Arrays of
Objects (cont.)
 What if you want to perform an operation
specific to one of the types in the array?
– Can use the instanceOf operator to determine
the specific type of element in the array
 Most general arrays have type Object.
– Can hold any type of object

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The Class java.util.ArrayList
 Contains sequence of elements ordered by
position
– 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.
– Size automatically adjusted as needed
 The positions available for access range from 0 to
the logical size minus 1.

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The Class java.util.ArrayList
(cont.)
 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:

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The Class java.util.ArrayList
(cont.)
Table 11-6: Some commonly used ArrayList methods

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The Class java.util.ArrayList
(cont.)
 ArrayList objects cannot directly store
primitive types.
– Must use wrapper classes
 Classes that contain the value of a primitive type
 Boolean, Integer, Double, Character

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The Class java.util.ArrayList
(cont.)
 ArrayList objects automatically “box” and
“unbox” primitive values when used with
ArrayList methods.

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The Class java.util.ArrayList
(cont.)
 Advantages of ArrayList over arrays:
– 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

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Graphics and GUIs: Menus
 A drop-down menu system consists of a
menu bar, a number of menus, and several
selections for each menu.
– 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)

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Graphics and GUIs: Menus (cont.)
Figure 11-6: New user interface for the
student test scores program
 Listener objects are attached to menus.
– When menu items are selected, events are fired
and the listener objects respond.

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Graphics and GUIs: Menus (cont.)
Example 11.6: TestScoresView class (with menus)

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Graphics and GUIs: Menus (Cont.)
Example 11.6: TestScoresView class (with menus, cont.)

43. Fundamentals of Java
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Summary
 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.

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Summary (cont.)
 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.

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Summary (cont.)
 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.

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Summary (cont.)
 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.