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1Java

Methods and Inner

ClassPart II

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2Java

Overloading with var-args10

Overloading9

Accessing var-args8

Var-args7

Changing array contents in a method6

Changing the member variable value of an object reference that is passed5

Passing reference type4

What is happening?3

Passing primitive type2

Arguments passing1

Contents

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3Java

Test your understanding20

Static Inner Class19

Result of execution18

Creating InnerClass instance17

Non static inner class16

Types of Inner Class15

Inner class14

Non-Static Initializer13

Static Initializer12

Initializers11

Contents

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4Java

know

Argument passing

var-arg

Method overloading

Initializers

Inner classes and static inner classes

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5Java

Be Able To

Implement method overloading

Use inner classes and static inner classes

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6Java

Arguments passing

Arguments passing in java is always pass by

value.

Two types of arguments can be passed in amethod call

-- Primitive type -- Reference type

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7Java

Passing primitive type

public class StudentTest{

public static void swap(int reg1,intreg2){

int temp;

temp=reg1;

reg1=reg2;reg2=temp; }

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8Java

public static void main(String args[]){

int r1=10, r2=20;swap(r1,r2);

System.out.println(r1=+ r1);

System.out.println(r2=+r2);

}

}

The program prints r1=10 and r2=20.

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9Java

main()

r1=10, r2=20

swap(r1,r2)

reg1=20,reg2=10

Changes made in swap

is not reflected in main()

Stack

What is happening?

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10Java

Passing reference type

public class StudentTest{public static void swap(Studentp,Student q){

Student temp;temp=p;

p=q;

q=temp;

}Folder 2

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11Java

public static void main(String a[]){

Student s1=new Student(John);Student s2=new Student(Mary);

swap(s1,s2);

System.out.println(s1=+s1.getName());

System.out.println(s2=+ s2.getName()

}

}The program prints :

s1=John

s2=Mary

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12Java

main()

s2s1

swap(s1,s2)

qp

John..

Mary..

stack

heap

After swap() s1 and s2 of main remains unchanged and p and

q are no longer available.

Ch i th b i bl

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13Java

Changing the member variable

value of an object reference that is

passedpublic class StudentTest{public static void change(Student p){

p.setName(Mary); }public static void main(String args[]){

Student s1=new Student(John);

change(s1);System.out.println(s1=+s1.getName());}}

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t k

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14Java

main()

s1

change(s1)

p

John

stack

heap

Mary

Change made to the member variable name reflected inmain().

Prints Mary.

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15Java

public class StudentTest{public static void sort(Student s[]){

Student temp;

for(int i=0;i

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}}}

public static void main(String args[]){

Student s1[]=new Student[2];

s1[0]=new Student("Mary");

s1[1]=new Student("John");

sort(s1);

for(int i=0;i

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17Java

main()

s1

sort(s1)

s

Mary..

John..

stack

heap

Changes made to the array content reflected in the main method.

0

1

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18Java

What is the result when you execute the following?

class StudentTest{

public static void main(String args[]){Student s1[]=new Student[2];s1[0]=new Student("Mary");s1[1]=new Student("John");change(s1);for(int i=0;i

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19Java

Var-args

This is a new feature in 1.5 .

Allows you to specify that a method can take multiple

arguments of same type. The number arguments

may be 0, one or more.void go(int x)

void go(char c, int x)

void go(Animal a)

In a method only the last argument can be of variablelength.

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20Java

Accessing var-args

public class Person{

public Person(String name, Stringnicknames)

{if(nicknames.length!=0){

for(String nm:nicknames)

System.out.println(nm);

System.out.println(nicknames[0]);

} }} Folder 6

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21Java

Can you write main() methodas

public static void

main(String... args)

instead of args[] ?

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22Java

What is the difference between an array and

var-args? (Are bothstatic void vararg1(int[] i) &

static void vararg2(int i))

same ?)

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23Java

Overloading

public class CollegeUtility {

public static voidsortStudent(Student s[]){

..}

public static voidsortCollege(College c[]){

..}

public static voidsortFaculties(Faculty c[])

{..}}

So

many

sort

method

names !

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24Java

public class CollegeUtility {

public static void sort(Students[]){..}

public static void sort(College

c[]){..}public static void sort(Facultyc[]){..}

public static void sort(Facilityc[]){..}

}Overloading sort method much simpler

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25Java

List1:All the methods where the name

and number of arguments of calling

method == name and number of

arguments of called method

List1 is empty Error

List2 contains > 1 element

List2: From list1, find all themethods that exactly match

the argument type ofcalling method.

yes

yes

no

Overloaded method

resolution

Error: No matching

method found

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26Java

no

List3: Find all the methods from

List1 where arguments of

calling methods areautomatically convertibleinto arguments of calledmethods.

List3 contains= 1 element

no

List2 contains 1 element

no

Matching method found

yes

yes

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27Java

no

List3 contains 0 elementyes

Error

no

List4: Find among the

methods in List 3 methods

which are more specific

List4 contains 1 element Matching method found

Error

yes

no

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28Java

Examples//exact match

public class StudentTest{

public static void display(int regno){

System.out.println(Registration No."+regno);

}public static void display(String name){System.out.println(Name. "+name);}

public static void main(String str[]){

Student s1=new Student(Mary);

display(s1.getName());

display(s1.getRegNo());

}}Folder 8

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29Java

//automatic conversion

public class StudentTest{

public static void display(long regno){System.out.println(Registration No."+regno);

}

public static void display(String name){System.out.println(Name. "+name);}

public static void main(String str[]){

Student s1=new Student(Mary);display(s1.getRegNo());

}}

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//more specific

public class Fee {

int id;

double amtPaid;

void pay(int id,double amt){

this.id=id;

amtPaid=amt;

}

void pay(int id,float amt) {

this.id=id;

amtPaid=amt; }

public static voidmain(String[] args){

Fee f1= newFee();

f1.pay(123,400);

}

}

Look at the conversion

sequence to find out whichargument is more specific.

Slide 34 of Nuts and Bolts

Folder 10

http://../Java/mod_Instructor_slides/3.%20Nuts%20and%20Bolts.ppthttp://../Java/mod_Instructor_slides/3.%20Nuts%20and%20Bolts.ppt

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31Java

//ambiguous

public class StudentManager{

public static void

changeSemester(int id, long sem){

}

public static voidchangeSemester(long id, int seam){

}

public static void main(String str[]){changeSemester(1,2);}

}

Automatic

conversion

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32Java

class AddVarargs {

static void go(int x, int y){ System.out.println("int,int");}static void go(byte... x){ System.out.println("byte... ");}public static void main(String[] args){

byte b = 5;go(b,b);}}

Overloading with var-args

Folder 11

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33Java

static void vararg(int[] i){}

static void vararg(int... x){}

cannot be overloaded.

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34Java

Initializers

Initializers are blocks of code that are used to

initialize member variables.

a) Static Initializers

b) Non-Static Initializers

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35Java

But I can declare and initialize variables

in same line like this:

class X{

int var=1; }

Why will I require a block of code ?

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36Java

Let us say that you initialize

your variables after readingtheir values from a file.

Reading from a file requires a

sequence of operations at the

minimum - opening a file,

reading and then closing a file

this means a block of java

statements. This cannot be

done in one statement like

yours. So we do this ininitializers !

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37Java

Yes, you can certainly put them in

the constructor. But if you have

more than one constructor thenrepeating the same code everywhere

would be a pain. Also note that if

you want to initialize your static

variables in the similar way beforethe object is created then static

initializer is the only place !

I can put that code in

the constructor !

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38Java

Static Initializer

public class CollegeConstants{

public static final int YEAR_OF_INCEPTION;

public static final String COLLEGE_NAME ;

static{

/*

Open the file and set the required

YEAR_OF_INCEPTION, COLLEGE_NAME*/

}

Static block

Non Static Initializer

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39Java

Non-Static Initializerpublic class OldStudent {

{private int regNo;

private String name;

{/*

Open the file and set the required reg_no, nameof each student

*/

}

}

Non-Static block

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40Java

To understand what gets called

when, we shall execute the codegive below.

public class W{

public W(){

System.out.println("W constructor"); }}

public class Z{

W w= new W();

{

System.out.println("instance block");

} Folder 12

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41Java

static{

System.out.println("static block");}

public Z(){

System.out.println("Z constructor");}

public static void main(String st[]){

new Z();}

}

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42Java

Output:

static block

W constructor

instance block

Z constructor

Can you guess what will be printed

if you comment new Z() in

main()?

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43Java

Inner class

An inner class is a class defined inside the scope of

another class. It is also called Nested class.

The class inside which the inner class is defined iscalled outer class.

Inner class can access all members of the outer classincluding private members.

Based on where the inner class is defined, the inner

class can be classified into two types.

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44Java

Member class

Non Static Inner Class or simply inner

class

Static Inner Class

Local Inner Class

Local named class or simply local innerclass

Anonymous Inner Class

Types of Inner Class

Note that in some books they dont

consider static inner classes as

inner classes. They are just

considered as nested classes.

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45Java

Non static inner class Structure:

public class OuterClass{

public class InnerClass{..}

}

Non static inner class object cannot be created

without a outer class object.

The private fields and methods of the member classes

are available to the enclosing class. The private fieldsand methods of the member classes are also available

to other member classes.

Can be declared as private, default orprotected.

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46Java

OuterClass out= new OuterClass();OuterClass.InnerClass in=out.new

InnerClass();

Or

OuterClass.InnerClass in=newOuterClass().new InnerClass();

Within OuterClass, InnerClass object can be createdby

InnerClass in=new InnerClass();

Creating InnerClass instance

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47Java

Example: linked list Node class can be viewed as inner class of

LinkedList class because Node class as astandalone class does not make any sense by

itself.

We will look at implementing a SinglyLinkedListclass with following options:

Inserting at the head, at the tail

Finding a particular node given an index.

Deleting a particular node given an index.

Printing nodes

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48Java

public class SinglyLinkedList{

private Node headNode;

private int noOfNodes=0;

class Node {

private Node nextNode;private String currentObject;

public String toString() {String s=(String)(currentObject);

return s;

}

}

Inner class

headNode

null

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49Java

public StringinsertFirst(Object addobj) {Node tempNode = new Node();

tempNode.currentObject=addobj;noOfNodes++;

if (headNode==null)headNode=tempNode;

else {

current=headNode;headNode=tempNode;

headNode.nextNode = current;}return

(String)headNode.currentObject;}

First node

tempNode

headNode

headnode

current

tempNode

null

null

null

private member of Node class

bli St i i tL t(Obj t dd bj) {

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50Java

public String insertLast(Object addobj) {Node create=new Node();create.currentObject=addobj;

noOfNodes++;if(headNode==null)headNode=create;

else {

Node tempNode = headNode;while(tempNode.nextNode!=null) {tempNode = tempNode.nextNode;}

tempNode.nextNode=create;}

return (String)create.currentObject;}

create

headNodeFirst node

Iterate till the end ofthe list and get the

last node.

headNode

tempNode

create

public String findNode(int index){Inappropriate index

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51Java

if(index>noOfNodes) return null;

Node tempNode = headNode;

int i=0;while(i++!=index)tempNode=tempNode.nextNode;return tempNode;}

public Node deleteNode(int index) {if(index>=noOfNodes) return null;

Node tempNode = headNode;

noOfNodes--;if(index==0){headNode=headNode.nextNode;return tempNode;}

headNode

0 1

Inappropriate index

For index=1

tempNode returned

Deletion of the first nod

headNode

returned

dIterate till you find the correcti d

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52Java

Node prevNode=null;int i=0;while(i++!=index){

prevNode=tempNode;tempNode=tempNode.nextNode; }

if(i==noOfNodes+1){

prevNode.nextNode=null;}

elseprevNode.nextNode=tempNode.nextNode;return tempNode;}

}

Deleting index=1

headNode

prevNode

0 1 2

Last Node

headNode

prevNode2

tempNode

tempNode

null

returned

returned

index.

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53Java

public String toString() {String s="";

for(Node n=headNode;n!=null;n=n.nextNode)s=s+"\n"+((String)(n.currentObject.toString()));

return s;}}//end of class

This should be pretty straight forward now!

class SampleTest {

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54Java

public static void main(String args[]) SinglyLinkedList s = new SinglyLinkedList();SinglyLinkedList.Node n;

//Insertions.insertFirst("Rama");s.insertLast("Sita");s.insertFirst("Hanuman");

s.insertLast("Ravana");// printingSystem.out.println("\nPrinting list

\n"+s.toString());

//Deletion

int temp=3;

How would you create

an instance of Node

class inside this class?

if(n==null)

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if(n==null)System.out.println("Invalid ID");

else

System.out.println("Deleting " +n);//Searchtemp=2;if((n=s.findNode(temp))==null)System.out.println(" Invalid ID");

elseSystem.out.println("Found "+ n);

// printingSystem.out.println("\nPrinting list

\n"+s.toString());}

}

Result of execution

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56Java

Result of execution

Printing list

Hanuman

Rama

Sita

Ravana

Deleting Ravana

Found Sita

Printing list

Hanuman

Rama

Sita

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57Java

In lab find out what .class

files are generated when

you compile the LinkedList

class ?

Static Inner Class

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58Java

Static Inner Class A static inner class is a class thats a static member of

the outer class which can access only static members ofthe outer class(including private members). It is alsocalled top-level class.

Structure:

public class OuterClass{public static class InnerClass{} }

Creating instance: Outside the outer class:OuterClass.InnerClass sinner=new OuterClass.InnerClass();

Inside the outer class:InnerClass inner=new InnerClass();

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59Java

Why static inner class

cannot access instance

members of the outer

class?

class Sort{

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private static void insertionSort(int[] a,int s, int temp) {

int j = s;while (j > 0 && a[j-1] > temp){

a[j] = a[j - 1];j--;}a[j] = temp;}

private static int binarySearch(int numbers[],int key ){

int low,high;int div=numbers.length;

low=0;

No. of elements currently in the array

Sorted arrayNew element to be addedto a in sorted position

slide elements down to

make room

Sorted array

Search elementFolder 14

high=numbers.length-1;

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61Java

while(true){div=(low+high)/2;if(key>numbers[div])

low=div+1;else if (key high) return -1;

}}

static class List{private int capacity;private int size;private int[] nums;

List(int capacity){

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62Java

this.capacity=capacity;nums=new int[capacity];

}

public void add(int i){if(capacity==size) {System.out.println("Over flow");return;

}insertionSort(nums,size,i);size++;}

public void search(int i){

int pos=-1;if((pos=binarySearch(nums,i))!=-1)elseSystem.out.println("\nNot Found ");

}

private static methodsof the outer class

public void display(){

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63Java

public void display(){for(int i=0;i

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64Java

Test your understandingclass E {

E() {System.out.print("E");}

static class Z {Z(){

System.out.print("Z");}}

public static void main(String args[]){

new E.Z();}}What is the result of attempting to compile and run the

program?

class B {

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65Java

private static String s1 = "s1";final String s2 = "s2";

B () {new Z("s5","s6");}static class Z {final String s3 = "s3";static String s4 = "s4";

Z (final String s5, String s6){

System.out.print(???);}}

public static void main(Stringargs[]) {new B();}}Which variable cannot be substituted for ???

without causing a compile-time error?

class F {

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66Java

{public void m1() {Z.m1();}

private static class Y {

private static void m1() {System.out.print("Y.m1 ");}}private static class Z {

private static void m1(){System.out.print("Z.m1 ");Y.m1();

}}

public static void main(String[] args){new F().m1();}}What is the result of attempting to compile and run the

program?

class Outer {

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67Java

{static class StaticNested {

static final int a = 25; // 1

static final int b; // 2static int c; // 3int d; // 4static {b = 42;} // 5

}class NonStaticInner {static final int e = 25; // 6static final int f; // 7

static int g; // 8int h; // 9static {f = 42;} // 10

}}Compile-time errors are generated at which lines?

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There are two more types of inner

class: Local and Anonymous

Inner class. We will look at themafter Interfaces.

Thanks !