CSI1390 – Java Programming Methods II Instructor: Saeid Nourian

Methods  Many names: –Method, function, procedure, subroutine, Macro  Java Syntax ( ) ( )  Example: int doWork (int duration) { return (duration * WORK_LOAD); }

Parameter Passing Types of Parameter Passing:  Passing Value –Primitive types  Passing Reference –Arrays –Objects

Passing Values 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; } 12 a 5 b 5 b a Stack Memory tmp swap scope main scope Does not work!

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!

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!

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)

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!

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!

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

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; }

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"); }