Week 10

1
Week 10

• Introduction to Computer Science and
  Object-Oriented Programming
• COMP 111
• George Basham

2
Week 10 Topics

• 10.1.1 Wrappers and Auto-boxing
• 10.1.2 The Enhanced for Loop
• 10.1.3 Partially Filled Arrays
• 10.1.4 Common Array Algorithms
• 10.1.5 Regression Testing
• 10.1.6 Two-dimensional Arrays

3
10.1.1 Wrappers and Auto-boxing

• Because numbers are not objects in Java, you
  cannot directly enter them in array lists
• For example, this will not compile
• ArrayListltdoublegt data new ArrayListltdoublegt()
  // No
• To store sequences of numbers in an array list,
  you must turn them into wrapper classes

4
10.1.1 Wrappers and Auto-boxing Cont.
Primitive Type Wrapper Class
byte Byte
boolean Boolean
char Character
double Double
float Float
int Integer
long Long
short Short
5
10.1.1 Wrappers and Auto-boxing Cont.

• Beginning with Java 5.0, if you assign a
  primitive type to a wrapper class, the conversion
  is automatic (called auto-boxing)
• Double d 29.95
• Conversely, beginning with Java 5.0, wrapper
  classes are automatically converted to primitive
  types (called auto-unboxing)
• double x d

6
10.1.1 Wrappers and Auto-boxing Cont.

• This will work to store simple number types in an
  array list
• ArrayListltDoublegt data new ArrayListltDoublegt()
  // Yes
• data.add(29.95)
• double x data.get(0)

7
10.1.2 The Enhanced for Loop

• Java version 5.0 introduces a very convenient
  shortcut for a common loop type, when you need to
  iterate through an sequence of elements
• The new loop construct is know as the for each
  loop
• The for each loop has a very specific purpose,
  traversing the elements of a collection from the
  beginning to the end

8
10.1.2 The Enhanced for Loop Cont.

• double data new double100
• assume that array is then populated
• double sum 0
• for (double e data)
• sum sum e

9
10.1.2 The Enhanced for Loop Cont.

• ArrayListltBankAccountgt accounts new
  ArrayListltBankAccountgt()
• assume that array list is then populated
• double sum 0
• for (BankAccount a accounts)
• sum sum a.getBalance()

10
10.1.3 Partially Filled Arrays

• Since an array is fixed in length, and every
  element may not be populated with a value, we
  need to make sure not to access an element of an
  array that does not contain a valid value
• For an array of object references, this is even
  more important from the aspect that calling a
  method on a null reference will throw a runtime
  exception

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10.1.3 Partially Filled Arrays Cont.

• With a partially filled array, keep a companion
  variable to track how many elements are used
• public static final int LEN 100
• private int values new intLEN
• private valSize 0 // companion var

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10.1.3 Partially Filled Arrays Cont.

• public int addElement(int inVal)
• if (this.valSize gt LEN)
• return -1
• this.valuesthis.valSize inVal
• // element index will be returned
• // then incremented for next use
• return this.valSize

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10.1.4 Common Array Algorithms

• Demonstrated
• Counting Matches
• Searching for a Value (linear search)
• Finding the Maximum or Minimum
• Also (refer to textbook) Filling, Computing Sum
  and Average Values, Locating the Position of an
  Element, Removing an Element, Inserting an
  Element, Copying and Growing an Array, Printing
  Element Separators

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10.1.4 Common Array Algorithms Cont.

• Counting Matches
• double atLeast 5000.00
• int matches 0
• for (BankAccount a accounts)
• if (a.getBalance() gt atLeast)
• matches
• System.out.println(matches)

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10.1.4 Common Array Algorithms Cont.

• Searching for a Value (linear search)
• int accountNumber 1001
• for (BankAccount a accounts)
• if (a.getAccountNumber()
• accountNumber)
• System.out.println
• (a.getBalance()) break

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10.1.4 Common Array Algorithms Cont.

• Finding the Maximum or Minimum
• BankAccount max accounts.get(0)
• for (int i 1 i lt accounts.size() i)
• BankAccount a account.get(i)
• if (a.getBalance() gt max.getBalance())
• max a
• System.out.println(max.getAccountNumber())

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10.1.5 Regression Testing

• A test suite is a set of tests for repeated
  testing
• Regression testing involves repeating previously
  run tests to ensure that known failures of prior
  versions do not appear in new versions of the
  software
• Refactoring seeks to improve the internal design
  and implementation of code without affecting its
  externally visible behavior

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10.1.6 Two-Dimensional Arrays

• int table new int23
• The array identified by table will have 2 rows
  (the row is the FIRST subscript) and 3 columns
  (the column is the SECOND subscript).

00 01 02
10 11 12
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10.1.6 Two-Dimensional Arrays Cont.

• table00 22
• table01 1301
• . . .
• table12 43
• // Traversing the 2-D array
• for (int i 0 i lt 2 i) // rows
• for (int j 0 j lt 3 j) // cols
• System.out.println(tableij

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Reference Big Java 4th Edition by Cay Horstmann

• 10.1.1 Wrappers and Auto-boxing (section 7.3 in
  Big Java)
• 10.1.2 The Enhanced for Loop (section 7.4 in Big
  Java)
• 10.1.3 Partially Filled Arrays (section 7.5 in
  Big Java)
• 10.1.4 Common Array Algorithms (section 7.6 in
  Big Java)
• 10.1.5 Regression Testing (section 7.7 in Big
  Java)
• 10.1.6 Two-dimensional Arrays (section 7.8 in
  Big Java)