Chapter 1.pdf

Ahmad Khoj King Abdulaziz University KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ KING ABDULAZIZ UNIVERSITY Chapter 1 Methods KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Introducing Method...

Ahmad Khoj King Abdulaziz University KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ KING ABDULAZIZ UNIVERSITY Chapter 1 Methods KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Introducing Methods A method is a collection of statements that are grouped together to perform an operation. Define a method Invoke a method modifier return value type method name formal parameters method public static int max(int num1, int num2) { int z = max(x, y); header int result; method actual parameters body parameter list (arguments) if (num1 > num2) result = num1; else result = num2; return value return result; } 3 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Introducing Methods, cont. Method signature is the combination of the method name and the parameter list. The variables defined in the method header are known as formal parameters. When a method is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. 4 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Introducing Methods, cont. A method may return a value. The returnValueType is the data type of the value the method returns. If the method does not return a value, the returnValueType is the keyword void. For example, the returnValueType in the main method is void. 5 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Calling Methods, cont. pass the value of i pass the value of j public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 6 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation i is now 5 public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 7 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation j is now 2 public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 8 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation invoke max(i, j) public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 9 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation invoke max(i, j) Pass the value of i to num1 Pass the value of j to num2 public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 10 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation declare variable result public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 11 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation (num1 > num2) is true since num1 is 5 and num2 is 2 public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 12 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation result is now 5 public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 13 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation return result, which is 5 public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 14 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation return max(i, j) and assign the return value to k public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 15 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬ animation Trace Method Invocation Execute the print statement public static void main(String[] args) { public static int max(int num1, int num2) { int i = 5; int result; int j = 2; int k = max(i, j); if (num1 > num2) result = num1; System.out.println( else "The maximum between " + i + result = num2; " and " + j + " is " + k); } return result; } 16 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Passing Parameters public static void nPrintln(String message, int n) { for (int i = 0; i < n; i++) System.out.println(message); } Suppose you invoke the method using nPrintln(“Welcome to Java”, 5); What is the output? Suppose you invoke the method using nPrintln(“Computer Science”, 15); What is the output? 17 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  CAUTION A return statement is required for a nonvoid method. The following method is logically correct, but it has a compilation error, because the Java compiler thinks it possible that this method does not return any value. public static int sign(int n) { if (n > 0) return 1; else if (n == 0) return 0; else if (n < 0) return –1; } To fix this problem, delete if (n num2) return num1; else return num2; } You can create more than methods in the same name if one of the following conditions is met: - Change datatype of parameters - Rearrange datatype of parameters - Change number of parameters 23 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  change datatype of parameters Overloading Methods Error 24 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Rearrange datatype of parameters Overloading Methods Error 25 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  change number of parameters Overloading Methods Error 26 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Overloading Methods Output: Output: First method Second method 27 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Ambiguous Invocation Sometimes there may be two or more possible matches for an invocation of a method, but the compiler cannot determine the most specific match. This is referred to as ambiguous invocation. Ambiguous invocation is a compilation error. 28 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Ambiguous Invocation 29 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Overloading Methods 30 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  The Math Class 31 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Create the following methods to calculate area of (Triangle and Rectangle): 1. public static void triangleArea (double base , double height) 2. public static double recArea(double length , double width)  What you should have inside each method: 1. triangleArea method: calculate triangle area using this formula: triangle = 0.5 * base * height 2. recArea method: calculate rectangle area using this formula: rectangle = length * width  Main – Make decision by using switch to choose which area will be calculated – When user chooses one, prompt him to enter base and height for triangle – When user chooses two, prompt him to enter length and width for rectangle – When user chooses other numbers, display this message “Wrong Choice” 32 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  33 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬  Benefits of Methods Write a method once and reuse it anywhere. Information hiding: hide the implementation from the user. Reduce complexity. 34 KING ABDULAZIZ UNIVERSITY ‫جامعة الملك عبد العزيز‬