CSI1390 – Java Programming Methods II

1. CSI1390 – Java ProgrammingMethods II Instructor: Saeid Nourian snourian@site.uottawa.ca

2. Methods • Many names: • Method, function, procedure, subroutine, Macro • Java Syntax <type> <func name> ( <parameters> ) • Example: int doWork (int duration) { return (duration * WORK_LOAD); }

3. Parameter Passing Types of Parameter Passing: • Passing Value • Primitive types • Passing Reference • Arrays • Objects

4. tmp <Garbage> main scope swap scope a a b b 12 5 5 12 Passing Values Does not work! void main() { int a = 12; int b = 5; swap (a, b); System.out.print(a+“,”+ b); } void swap (int a, int b) { int tmp; tmp = a; a = b; b = tmp; } Stack Memory 12 12 5

5. Passing References void main() { Integer a = new Integer(); a.value = 12; Integer b = new Integer(); b.value = 5 swap (a, b); System.out.print(a+”,”+b); } void swap (Integer a, Integer b) { Integer tmp = new Integer(); tmp.value = a.value; a.value = b.value; b.value = tmp.value; } Works!

6. Passing References void main() { Integer a = new Integer(12); Integer b = new Integer(5); swap (a, b); cout << a << b; } void swap (Integer a, Integer b) { Integer tmp; tmp = a; a = b; b = tmp; } Does not work!

7. Passing References void foo4 (int z[]) { } void foo2 (int z[][]) { } int[] a1 = new int[3]; foo1 (a1) int[][] a2 = new int[2][2]; foo3 (a2)

8. Passing References void main() { int[] myArray = new int[] {12, 5}; swap (myArray, 0, 1); System.out.print(myArray[0]+“,”+ myArray[0]); } void swap (int array[], int i, int j) { int tmp; tmp = array[i]; array[i] = array[j]; array[j] = tmp; } Works!

9. Passing References // Swaps a[i] with a[j]. private static void swap(int[] a, int i, int j) { if (i == j) return; int temp = a[i]; a[i] = a[j]; a[j] = temp; } Works!

10. Returning Values • Functions return a new copy of the “value” or “reference” • The following function: int func_1 () { int a = 7; return a; } • Returns the value 7

11. Returning Values & References // return value (primitive value) int getValue () { int v = 10; return v; } // return reference (object) String getLocalObject () { String s = new String(“7”); return s; } // return reference (array) int[] getArray () { int[] a = new int[] {7,9,10}; return a; }

12. Bubble Sort public static void bubbleSort(int[] a) { int numSwaps = 0; for (int i = 0; i < a.length; i++) for (int j = 1; j < a.length - i; j++) if (a[j-1] > a[j]) { swap(a, j-1, j); numSwaps++; } System.out.println(numSwaps + " swaps"); }