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Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

Chapter 3: Using Objects Objectives. Object-Oriented Program Intro to Objects and Classes Roles of Constructor & Methods String Class String Operations and Methods Prepares you for defining your own classes and creating and manipulating the objects of those classes.

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Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

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  1. Chapter 3: Using Objects Objectives • Object-Oriented Program • Intro to Objects and Classes • Roles of Constructor & Methods • String Class • String Operations and Methods • Prepares you for defining your own classes and creating and manipulating the objects of those classes Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  2. Values versus Objects, Objects and Variables • Numbers • Have values but they do have behaviors • Objects • Have attributes and behaviors • System.in • References an InputStream • Attribute: keyboard • Behaviors: reading • System.out • References an OutputStream • Attribute: monitor • Behaviors: printing

  3. Other Java object types • String • Rectangle • Color • JFrame Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  4. Representation

  5. Shorthand representation Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  6. Examples • Consider String a = "excellence“; String b = a; • What is the representation? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  7. Examples • Consider String a = "excellence“; String b = a; • What is the representation? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  8. Examples The first two parameters of the int x = 3; int y = 4; position of the upper-left-hand int width = 5; corner of the new Rectangle int height = 2; new Rectangle r = Rectangle(x, y, width, height); The third and fourth parameters of the Rectangle constructor the new Rectangle Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  9. Examples

  10. Uninitialized versus null • Consider String dayOfWeek; BufferedReader inStream; Rectangle frame; • What is the representation? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  11. Uninitialized versus null • Consider String dayOfWeek; BufferedReader inStream; Rectangle frame; • What is the representation? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  12. Uninitialized versus null • Consider String fontName = null; BufferedReader fileStream = null; Rectangle boundingBox = null; • What is the representation? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  13. Assignment • Consider String word1 = "luminous"; String word2 = "graceful"; Word1 = word2; • Initial representation Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  14. Assignment • Consider String word1 = "luminous"; String word2 = "graceful"; Word1 = word2; • After assignment Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  15. Final variables • Consider final String POEM_TITLE = “Appearance of Brown"; final String WARNING = “Weather ball is black"; • What is the representation? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  16. Final variables Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  17. Final variables • Consider final Rectangle BLOCK = new Rectangle(6,9,4,2); BLOCK.setLocation(1,4); BLOCK.resize(8,3); • Initial representation Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  18. Final variables • Consider final Rectangle BLOCK = new Rectangle(6,9,4,2); BLOCK.setLocation(1,4); BLOCK.resize(8,3); • Initial representation Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  19. Final variables • Consider String LANGUAGE = "Java"; Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  20. Using objects • Consider BufferedReader stdin = new BufferedReader( new InputStreamReader(System.in)); System.out.print("Enter your account name: "); String response = stdin.readLine(); Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  21. Using objects • Consider BufferedReader stdin = new BufferedReader( new InputStreamReader(System.in)); System.out.print("Enter your account name: "); String response = stdin.readLine(); Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  22. Using objects • Consider BufferedReader stdin = new BufferedReader( new InputStreamReader(System.in)); System.out.print("Enter your account name: "); String response = stdin.readLine(); • Suppose the user interaction is Enter your account name: artiste Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  23. String representation • Consider • String alphabet = "abcdefghijklmnopqrstuvwxyz"; • Standard shorthand representation • Truer representation

  24. String representation • Consider • String alphabet = "abcdefghijklmnopqrstuvwxyz"; • char c1 = alphabet.charAt(9); • char c2 = alphabet.charAt(15); • char c3 = alphabet.charAt(2); • What are the values of c1, c2, and c3? Why? Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  25. Program WordLength.java public class WordLength { public static void main(String[] args) throws IOException { BufferedReader stdin = new BufferedReader( new InputStreamReader(System.in)); System.out.print("Enter a word: "); String word = stdin.readLine(); int wordLength = word.length(); System.out.println("Word" + word + "haslength“ + wordLength + "."); } } Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  26. More String methods • Consider String weddingDate = "August 21, 1976"; String month = weddingDate.substring(0, 6); System.out.println("Month is " + month + "."); • What is the output? Month is August. Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  27. More String methods • Consider String fruit = "banana"; String searchString = "an"; int n1 = fruit.indexOf(searchString, 0); int n2 = fruit.indexOf(searchString, n1 + 1); int n3 = fruit.indexOf(searchString, n2 + 1); System.out.println("First search: " + n1); System.out.println("Second search: " + n2); System.out.println("Third search: " + n3); • What is the output? First search: 1 Second search: 3 Third search: -1 Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  28. More String methods • Consider int v1 = -12; double v2 = 3.14; char v3 = 'a'; String s1 = String.valueof(v1); String s2 = String.valueof(v2); String s3 = String.valueof(v3); Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

  29. Assignment 3 – Reading: Chapter 3 3-12. 3-13. 3-15. 3-17. 3-25. Week 2-3 05/23/2005 Course ISM4234-004 Dr. Simon Qiu

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