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Java Programming: From Problem Analysis to Program Design, 3e Chapter 7

Java Programming: From Problem Analysis to Program Design, 3e Chapter 7. User-Defined Methods. Chapter Objectives. Understand how methods are used in Java programming Learn about standard (predefined) methods and discover how to use them in a program Learn about user-defined methods

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Java Programming: From Problem Analysis to Program Design, 3e Chapter 7

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  1. Java Programming: From Problem Analysis to Program Design, 3eChapter 7 User-Defined Methods

  2. Chapter Objectives • Understand how methods are used in Java programming • Learn about standard (predefined) methods and discover how to use them in a program • Learn about user-defined methods • Examine value-returning methods, including actual and formal parameters Java Programming: From Problem Analysis to Program Design, 3e

  3. Chapter Objectives (continued) • Explore how to construct and use a value-returning, user-defined method in a program • Learn how to construct and use user-defined void methods in a program • Explore variables as parameters • Learn about the scope of an identifier • Become aware of method overloading Java Programming: From Problem Analysis to Program Design, 3e

  4. Predefined Classes • Methods already written and provided by Java • Organized as a collection of classes (class libraries) • To use: import package • Method type: data type of value returned by method Java Programming: From Problem Analysis to Program Design, 3e

  5. Predefined Classes (continued) Java Programming: From Problem Analysis to Program Design, 3e

  6. Predefined Classes (continued) Java Programming: From Problem Analysis to Program Design, 3e

  7. Predefined Classes (continued) Java Programming: From Problem Analysis to Program Design, 3e

  8. Predefined Classes (continued) Java Programming: From Problem Analysis to Program Design, 3e

  9. class Character(Package: java.lang) Java Programming: From Problem Analysis to Program Design, 3e

  10. class Character(Package: java.lang) (continued) Java Programming: From Problem Analysis to Program Design, 3e

  11. class Character(Package: java.lang) (continued) Java Programming: From Problem Analysis to Program Design, 3e

  12. Syntax: Value-Returning Method Java Programming: From Problem Analysis to Program Design, 3e

  13. User-Defined Methods • Value-returning methods • Used in expressions • Calculate and return a value • Can save value for later calculation or print value • modifiers: public, private, protected, static, abstract, final • returnType: type of the value that the method calculates and returns (using return statement) • methodName: Java identifier; name of method Java Programming: From Problem Analysis to Program Design, 3e

  14. Syntax • Syntax: Formal Parameter List -The syntax of the formal parameter list is: • Method Call -The syntax to call a value-returning method is: Java Programming: From Problem Analysis to Program Design, 3e

  15. Syntax (continued) • Syntax: Actual Parameter List -The syntax of the actual parameter list is: • Syntax: return Statement -The return statement has the following syntax: • return expr; Java Programming: From Problem Analysis to Program Design, 3e

  16. Equivalent Method Definitions public static double larger(double x, double y) { doublemax; if(x >= y) max = x; else max = y; returnmax; } Java Programming: From Problem Analysis to Program Design, 3e

  17. Equivalent Method Definitions (continued) public static doublelarger(doublex, doubley) { if(x >= y) returnx; else returny; } Java Programming: From Problem Analysis to Program Design, 3e

  18. Equivalent Method Definitions (continued) public static doublelarger(doublex, doubley) { if(x >= y) returnx; returny; } Java Programming: From Problem Analysis to Program Design, 3e

  19. Programming Example: Palindrome Number • Palindrome: integer or string that reads the same forwards and backwards • Input: integer or string • Output: Boolean message indicating whether integer string is a palindrome Java Programming: From Problem Analysis to Program Design, 3e

  20. Solution: isPalindrome Method public static boolean isPalindrome(String str) { int len = str.length(); int i, j; j = len - 1; for (i = 0; i <= (len - 1) / 2; i++) { if (str.charAt(i) != str.charAt(j)) return false; j--; } return true; } Java Programming: From Problem Analysis to Program Design, 3e

  21. Sample Runs: Palindrome Number Java Programming: From Problem Analysis to Program Design, 3e

  22. Sample Runs: Palindrome Number (continued) Java Programming: From Problem Analysis to Program Design, 3e

  23. Flow of Execution • Execution always begins with the first statement in the method main • User-defined methods execute only when called • Call to method transfers control from caller to called method • In method call statement, specify only actual parameters, not data type or method type • Control goes back to caller when method exits Java Programming: From Problem Analysis to Program Design, 3e

  24. Programming Example: Largest Number • Input: set of 10 numbers • Output: largest of 10 numbers • Solution • Get numbers one at a time • Method largest number: returns the larger of 2 numbers • For loop: calls method largest number on each number received and compares to current largest number Java Programming: From Problem Analysis to Program Design, 3e

  25. Solution: Largest Number static Scanner console = new Scanner(System.in); public static void main(String[] args) { double num; double max; int count; System.out.println("Enter 10 numbers."); num = console.nextDouble(); max = num; for (count = 1; count < 10; count++) { num = console.nextDouble(); max = larger(max, num); } System.out.println("The largest number is " + max); } Java Programming: From Problem Analysis to Program Design, 3e

  26. Sample Run: Largest Number • Sample Run: • Enter 10 numbers: • 10.5 56.34 73.3 42 22 67 88.55 26 62 11 • The largest number is 88.55 Java Programming: From Problem Analysis to Program Design, 3e

  27. Void Methods • Similar in structure to value-returning methods • Call to method is always stand-alone statement • Can use return statement to exit method early Java Programming: From Problem Analysis to Program Design, 3e

  28. Void Methods: Syntax • Method Definition • -The general form (syntax) of a void method without parameters is as follows: • modifier(s) void methodName() • { • statements • } • Method Call (Within the Class) -The method call has the following syntax: methodName(); Java Programming: From Problem Analysis to Program Design, 3e

  29. Void Methods with Parameters: Syntax Java Programming: From Problem Analysis to Program Design, 3e

  30. Void Methods with Parameters: Syntax (continued) Java Programming: From Problem Analysis to Program Design, 3e

  31. Primitive Data Type Variables as Parameters • A formal parameter receives a copy of its corresponding actual parameter • If a formal parameter is a variable of a primitive data type: • Value of actual parameter is directly stored • Cannot pass information outside the method • Provides only a one-way link between actual parameters and formal parameters Java Programming: From Problem Analysis to Program Design, 3e

  32. Reference Variables as Parameters • If a formal parameter is a reference variable: • Copies value of corresponding actual parameter • Value of actual parameter is address of the object where actual data is stored • Both formal and actual parameter refer to same object Java Programming: From Problem Analysis to Program Design, 3e

  33. Uses of Reference Variables as Parameters • Can return more than one value from a method • Can change the value of the actual object • When passing address, would save memory space and time, relative to copying large amount of data Java Programming: From Problem Analysis to Program Design, 3e

  34. Reference Variables as Parameters: type String Java Programming: From Problem Analysis to Program Design, 3e

  35. Reference Variables as Parameters: type String (continued) Example 7-11 public class Example7_11 { public static void main(String[] args) { int num1; //Line 1 IntClass num2 = new IntClass(); //Line 2 char ch; //Line 3 StringBuffer str; //Line 4 num1 = 10; //Line 5 num2.setNum(15); //Line 6 ch = 'A'; //Line 7 str = new StringBuffer("Sunny"); //Line 8 System.out.println("Line 9: Inside main: " + "num1 = " + num1 + ", num2 = " + num2.getNum() + ", ch = " + ch + ", and str = " + str); //Line 9 Java Programming: From Problem Analysis to Program Design, 3e

  36. Reference Variables as Parameters: type String (continued) funcOne(num1, num2, ch, str); //Line 10 System.out.println("Line 11: After funcOne: " + "num1 = " + num1 + ", num2 = " + num2.getNum() + ", ch = " + ch + ", and str = " + str); //Line 11 } Java Programming: From Problem Analysis to Program Design, 3e

  37. Reference Variables as Parameters: type String (continued) public static void funcOne(int a, IntClass b, char v, StringBuffer pStr) { int num; //Line 12 int len; //Line 13 num = b.getNum(); //Line 14 a++; //Line 15 b.addToNum(12); //Line 16 v = 'B'; //Line 17 len = pStr.length(); //Line 18 pStr.delete(0, len); //Line 19 pStr.append("Warm"); //Line 20 System.out.println("Line 21: Inside funcOne: \n" + " a = " + a + ", b = " + b.getNum() + ", v = " + v + ", pStr = " + pStr + ", len = " + len + ", and num = " + num); //Line 21 } } Java Programming: From Problem Analysis to Program Design, 3e

  38. Reference Variables as Parameters: type String (continued) Java Programming: From Problem Analysis to Program Design, 3e

  39. Reference Variables as Parameters: type String (continued) num1 = 10; //Line 5 num2.setNum(15); //Line 6 ch = 'A'; //Line 7 str = new StringBuffer("Sunny"); //Line 8 Java Programming: From Problem Analysis to Program Design, 3e

  40. Reference Variables as Parameters: type String (continued) System.out.println("Line 9: Inside main: " + "num1 = " + num1 + ", num2 = " + num2.getNum() + ", ch = " + ch + ", and str = " + str); //Line 9 Java Programming: From Problem Analysis to Program Design, 3e

  41. Reference Variables as Parameters: type String (continued) int num; //Line 12int len; //Line 13 num = b.getNum(); //Line 14 Java Programming: From Problem Analysis to Program Design, 3e

  42. Reference Variables as Parameters: type String (continued) num = b.getNum(); //Line 14 Java Programming: From Problem Analysis to Program Design, 3e

  43. Reference Variables as Parameters: type String (continued) a++; //Line 15 Java Programming: From Problem Analysis to Program Design, 3e

  44. Reference Variables as Parameters: type String (continued) b.addToNum(12); //Line 16 Java Programming: From Problem Analysis to Program Design, 3e

  45. Reference Variables as Parameters: type String (continued) v = 'B'; //Line 17 Java Programming: From Problem Analysis to Program Design, 3e

  46. Reference Variables as Parameters: type String (continued) len = pStr.length(); //Line 18 Java Programming: From Problem Analysis to Program Design, 3e

  47. Reference Variables as Parameters: type String (continued) pStr.delete(0, len); //Line 19 Java Programming: From Problem Analysis to Program Design, 3e

  48. Reference Variables as Parameters: type String (continued) pStr.append("Warm"); //Line 20 Java Programming: From Problem Analysis to Program Design, 3e

  49. Reference Variables as Parameters: type String (continued) System.out.println("Line 21: Inside funcOne: \n" + " a = " + a + ", b = " + b.getNum() + ", v = " + v + ", pStr = " + pStr + ", len = " + len + ", and num = " + num); //Line 21 Java Programming: From Problem Analysis to Program Design, 3e

  50. Reference Variables as Parameters: type String (continued) Java Programming: From Problem Analysis to Program Design, 3e

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