Transcript COS260Day15
COS 260 DAY 16 Tony Gauvin JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Agenda • Questions? • Assignment 3 not corrected • Still waiting for student submissions • Assignment 4 posted • All from chap 7 • Due Nov 10 @ 9:30 AM • Finish Chap 7 Arrays in Java • Programming Lab JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Ch 1 -2 Schedule for next two weeks • Oct 30 • More on Arrays • Nov 3 • Begin Inheritance, Polymorphism and Interfaces • Nov 6 • No Class, I am at a Board meeting in Lexington, KY • Nov 10 • Finish Inheritance, Polymorphism and Interfaces • Assignment 4 due JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved New Assignment Grading Criteria • Criteria 1 30 % Does the program compile with no errors or warnings? • Criteria 2 50% Does the program run and produce the intended outputs for the intended inputs? • Criteria 3 5% Is the Code properly Commented? • Criteria 4 5% Does the Code adhere to proper style and conventions for Java? • Criteria 5 10% Is the code an original creative work of the student? Using leveraged code without citation 0 Students submitting duplicate code as another student 0 JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Arrays Chapter 7 JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Objectives • Order (sort) the elements of an array • Search an array for a particular item • Define, use multidimensional array • Text fields, text areas in applets • Drawing arbitrary polygons in applets JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Sorting, Searching Arrays: Outline • Selection Sort • Other Sorting Algorithms • Searching an Array JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Selection Sort • Consider arranging all elements of an array so they are ascending order • Algorithm is to step through the array • Place smallest element in index 0 • Swap elements as needed to accomplish this • Called an interchange sorting algorithm JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Selection Sort • Figure 7.5a JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Selection Sort • Figure 7.5b ... JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Selection Sort • Algorithm for selection sort of an array JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Selection Sort • View implementation of selection sort, listing 7.10 class ArraySorter • Chapter 7 Code\ArraySorter.java • View demo program, listing 7.11 class SelectionSortDemo • Chapter 7 Code\SelectionSortDemo.java Sample screen output JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Other Sorting Algorithms • Selection sort is simplest • But it is very inefficient for large arrays • East to change from ascending to decending • Chapter 7 Code\ArraySorter2.java • Chapter 7 Code\SelectionSortDemo2.java • Java Class Library provides for efficient sorting • Has a class called Arrays • http://docs.oracle.com/javase/7/docs/api/java/util/Arrays.html • Class has multiple versions of a sort method JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Bubble sort (assignment 4 program 3) http://www.csit.parkland.edu/~mbrandyberry/CS1Java/Lessons/Lesson28/BubbleSort.htm JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Searching an Array • Method used in OneWayNoRepeatsList is sequential search • Looks in order from first to last • Good for unsorted arrays • Search ends when • Item is found … or … • End of list is reached • If list is sorted, use more efficient searches • Sort first • Search second • Fastest is binary search JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Multidimensional Arrays: Outline • Multidimensional-Array Basics • Multidimensional-Array Parameters and Returned Values • Java's Representation of Multidimensional • Ragged Arrays • Programming Example: Employee Time Records JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Multidimensional-Array Basics • Consider Figure 7.6, a table of values JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Multidimensional-Array Basics • Figure 7.7 Row and column indices for an array named table table[3][2] has a value of 1262 JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Multidimensional-Array Basics • We can access elements of the table with a nested for loop • Example: • View sample program, listing 7.12 class InterestTable • Chapter 7 Code\InterestTable.java JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Multidimensional-Array Basics Sample screen output JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Multidimensional-Array Parameters and Returned Values • Methods can have • Parameters that are multidimensional-arrays • Return values that are multidimensional-arrays • View sample code, listing 7.13 class InterestTable2 JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Java's Representation of Multidimensional Arrays • Multidimensional array represented as several onedimensional arrays • Given int [][] table = new int [10][6]; • Array table is actually 1 dimensional of type int[] • It is an array of arrays • Important when sequencing through multidimensional array JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Ragged Arrays • Not necessary for all rows to be of the same length • Example: JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Programming Example • Employee Time Records • Two-dimensional array stores hours worked • For each employee • For each of 5 days of work week • Array is private instance variable of class • View sample program, listing 7.14 class TimeBook • Chapter 7 Code\TimeBook.java JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Programming Example Sample screen output JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Programming Example • Figure 7.8 Arrays for the class TimeBook JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Graphics Supplement: Outline • Text Areas and Text Fields • Programming Example: A Question-and-Answer Applet • The Classes JTextArea and JTextField • Drawing Polygons JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Text Areas, Text Fields • Text area is object of class JTextArea • Displayed as a place for user to enter multiple lines of text • View sample code, listing 7.15 class Oracle • Chapter 7 Code\Oracle.java Sample screen output JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved JTextArea and JTextField • Class JTextArea • Used for multiple lines of user input • Class JtextField • Used for single line of user input • Both classes include methods • setText • getText JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Drawing Polygons • Class Graphics has method drawRect • But only 4 sides and only 90 degree corners • Method drawPolygon can draw polygon of any number of sides • Three arguments int for x values of coordinates • Array of int for y values of coordinates • Array of • Number of points (vertices) • A polyline like a polygon, not closed JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Drawing Polygons • Figure 7.9 A polygon and a polyline JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Drawing Polygons • View sample applet, listing 7.16 class House House is a filled polygon Door is a polyline Window is an ordinary polygon Sample screen output JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Summary • An array is a collection of variables all of the same type • Arrays are objects, created with operator new • Elements numbered starting with 0, ending with 1 less than length • Indexed variable can be used as a parameter – treated like variable of base type JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Summary • Entire array can be passed as parameter to a method • Method return value can be an array • Partially filled array usually stores values in initial segment, use an int to track how many are used • Privacy leak caused by returning array corresponding to private instance variable JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved Summary • Selection sort orders an array into ascending or descending order • Multidimensional arrays are implemented as an array of arrays • Treat two-dimensional array as a table with rows and columns • Text fields, text areas in an applet provide areas for text input/output • Possible to draw polygons, polylines in an applet JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch ISBN 0133862119 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved