CSI1390 – Java ProgrammingCSI1390 – Java Programming

Methods IIMethods II

Instructor: Saeid NourianInstructor: Saeid Nourian

snourian@site.uottawa.casnourian@site.uottawa.ca

MethodsMethods

Many names:Many names:– Method, function, procedure, subroutine, Method, function, procedure, subroutine,

MacroMacro Java SyntaxJava Syntax

<type> <func name> <type> <func name> (( <parameters> <parameters> )) Example:Example:

int doWork (int duration) {int doWork (int duration) {return (duration * WORK_LOAD);return (duration * WORK_LOAD);

}}

Parameter PassingParameter Passing

Types of Parameter Passing:Types of Parameter Passing: Passing Value Passing Value

– Primitive typesPrimitive types Passing ReferencePassing Reference

– ArraysArrays– ObjectsObjects

Passing ValuesPassing Values

void main() {void main() {int a = 12;int a = 12;int b = 5;int b = 5;swap (a, b);swap (a, b);System.out.print(a+“,”+ b);System.out.print(a+“,”+ b);

}}

void swap (int a, int b) {void swap (int a, int b) {int tmp;int tmp;tmp = a;tmp = a;a = b;a = b;b = tmp;b = tmp;

}} 12a

5b

5b

12a

Stack Memory

<Garbage>tmp 12

5

12

swap scope

main scope

Does not work!

Passing ReferencesPassing Referencesvoid main() {void main() {

Integer a = new Integer();Integer a = new Integer();a.value = 12;a.value = 12;Integer b = new Integer();Integer b = new Integer();b.value = 5b.value = 5swap (a, b);swap (a, b);System.out.print(a+”,”+b);System.out.print(a+”,”+b);

} }

void swap (Integer a, Integer b) {void swap (Integer a, Integer b) {Integer tmp = new Integer();Integer tmp = new Integer();tmp.value = a.value;tmp.value = a.value;a.value = b.value;a.value = b.value;b.value = tmp.value;b.value = tmp.value;

}}

Works!

Passing ReferencesPassing References

void main() {void main() {Integer a = new Integer(12);Integer a = new Integer(12);Integer b = new Integer(5);Integer b = new Integer(5);swap (a, b);swap (a, b);cout << a << b;cout << a << b;

}}

void swap (Integer a, Integer b) {void swap (Integer a, Integer b) {Integer tmp;Integer tmp;tmp = a;tmp = a;a = b;a = b;b = tmp;b = tmp;

}}

Does not work!

Passing ReferencesPassing References

void foo4 (int z[]) {void foo4 (int z[]) {

}}

void foo2 (int z[][]) {void foo2 (int z[][]) {

}}

int[] a1 = new int[3];int[] a1 = new int[3];foo1 (a1)foo1 (a1)

int[][] a2 = new int[2][2];int[][] a2 = new int[2][2];foo3 (a2) foo3 (a2)

Passing ReferencesPassing References

void main() {void main() {int[] myArray = new int[] {12, 5}; int[] myArray = new int[] {12, 5}; swap (myArray, 0, 1);swap (myArray, 0, 1);System.out.print(myArray[0]+“,”+ myArray[0]);System.out.print(myArray[0]+“,”+ myArray[0]);

}}

void swap (int array[], int i, int j) {void swap (int array[], int i, int j) {int tmp;int tmp;tmp = array[i];tmp = array[i];array[i] = array[j];array[i] = array[j];array[j] = tmp;array[j] = tmp;

}}

Works!

Passing ReferencesPassing References

// Swaps a[i] with a[j]. // Swaps a[i] with a[j]. private static void swap(int[] a, int i, int j) private static void swap(int[] a, int i, int j) { {

if (i == j) if (i == j) return; return;

int temp = a[i]; int temp = a[i]; a[i] = a[j]; a[i] = a[j]; a[j] = temp; a[j] = temp;

} }

Works!

Returning ValuesReturning Values

Functions return a new Functions return a new copycopy of the of the “value” or “reference” “value” or “reference”

The following function:The following function:int func_1 () {int func_1 () {

int a = 7;int a = 7;

return a;return a;

}} Returns the value 7Returns the value 7

Returning Values & ReferencesReturning Values & References// return value (primitive value)// return value (primitive value)int getValue () {int getValue () {

int v = 10;int v = 10;return v;return v;

}}

// return reference (object)// return reference (object) String getLocalObject () {String getLocalObject () {

String s = new String(“7”);String s = new String(“7”);return s;return s;

}}

// return reference (array)// return reference (array) int[] getArray () {int[] getArray () {

int[] a = new int[] {7,9,10};int[] a = new int[] {7,9,10};return a;return a;

}}

Bubble SortBubble Sort

public static void bubbleSort(int[] a) public static void bubbleSort(int[] a) { {

int numSwaps = 0; int numSwaps = 0; for (int i = 0; i < a.length; i++) for (int i = 0; i < a.length; i++)

for (int j = 1; j < a.length - i; j++) for (int j = 1; j < a.length - i; j++) if (a[j-1] > a[j]) { if (a[j-1] > a[j]) {

swap(a, j-1, j); swap(a, j-1, j); numSwaps++; numSwaps++;

} } System.out.println(numSwaps + " swaps"); System.out.println(numSwaps + " swaps");

} }