javasecond20.ppt

7/28/2019 JavaSecond20.ppt

1/20

Arrays

Creation of an Array involves 3 steps:

Declare the array

Create memory locations

Put values into the memory locations


2/20

Arrays

Arrays can be declared in two forms:

1. Type arrayname[ ];

2. Type[ ] arrayname;

Examples:

1. int number[ ];

2. float average[ ];

3. int[ ] coutner;

4. float[ ] marks;

* We do not enter the size of the array in the declaration.


3/20

Creation of Arrays

Arrayname= new type[size];

Number =new int[5];

Average=new float[10];

It is also possible to combine these twosteps:

int number[ ]=new int[5];


4/20

Initialization of Arrays

arrayname[subscript]=value;

Example:

Number[0]=35;

Or you can use loops to initialize an array


5/20

Two-Dimensional Arrays

int myArray[ ] [ ];

myArray=new int[3][4];

Or

int myArray[ ][ ]=new int[3][4];

Initializing 2-D arrays

int table[2][3]={

{0,0,0},

{1,1,1}};

Or through loops


6/20

Strings & StringBuffer

In Java, Strings are class objects and implemented usingtwo classes, namely, String and StringBuffer.

A java is not a character array and is not NULL

terminated. String stringName;

StringName=new String(string);

Or

String firstName=new String(Jaypee);

To get the length of the string:

int n=firstName.length( );

Concatenation using +


7/20

String Methods

s2=s1.toLowerCase( );

s2=s1.toUpperCase( );

s1.equals(s2)

s1.equalsIgnoreCase(s2) s1.length( );

s1.concat(s2)

s1.substring(n)

s1.substring(n,m) p.toString( )// Creates a string representation of object p

String. valueOf(variable) // Converts parameter value tostring representation


8/20

StringBuffer Class

It is a peer class of String. String creates strings offixed length. StringBuffer creates strings offlexible length that can be modified in terms of

both length and content.

StringBuffer str=new StringBuffer(objectlanguage);

s1.append(s2); s1.insert(n,s2) // inserts string s2 at position n of s1

s1.setLength(n)


9/20

Vectors

Vector is a generic dynamic array that can hold objects ofany type and any number

The objects do not have to be homogenous.

Arrays can be easily implemented as vectors

Vector intVect=new Vector( );

Vector list=new Vector(3);

Advantages over Array:

It is dynamic

Disadvantages over Array:

Cannot hold primitive data type (int, float etc)


10/20

Vector Methods

List.addElement(item)

List.elementAt(10);

List.size( )

List.removeElement(item)

List.removeElementAt(n) List.removeAllElements( )


11/20

Program With Vectors

class MyVector{

public static void main(String args[])

{

java.util.Vector v=new java.util.Vector();

v.addElement("Neha");

v.addElement("Mragendra");

v.addElement("Gaurav");

System.out.println(v);

v.removeElementAt(2); System.out.println(v);

}

}


12/20

Program using Import

import java.util.Vector;

class MyVector{

public static void main(String args[])

{

Vector v=new Vector();

v.addElement("Neha");

v.addElement("Mragendra");

v.addElement("Gaurav");

System.out.println(v);

v.removeElementAt(2); System.out.println(v);

}

}


13/20

Wrapper Classes

You know Vectors cannot handle primitive

data types like int , float, long ,char and

double.

So, what should we do?


14/20

Wrapper Classes

Ans: convert primitive types to object types

How?


15/20

Wrapper classes

Ans: Through the use of Wrapper classes

Simple Type Wrapper Class

boolean Boolean

char Character

double Double

float Floatint Integer

long Long


16/20

Converting Primitive Numbers to

Object Numbers Integer IntVal=new Integer(i);

Float FloatVal=new Float(f);

Double DoubleVal=new Double(d);

Long LongVal=new Long(l);


17/20

Converting Object Numbers to

Primitive Numbers using

typeValue() method

int i=IntVal.intValue( );

float f=FloatVal.floatValue( ); long l=LongVal.longValue( );

double d=DoubleVal.doublevalue( );


18/20

Converting Numbers to Strings

using toString( ) Method str=Integer.toString(i)

str=Float.toString(f);

str=Double.toString(d);

str=Long.toString(l);


19/20

Converting Numeric Strings to

Primitive Numbers Using Parsing

Method int i=Integer.parseInt(str);

long l=Long.parseLong(str);


20/20

Converting String objects to

Numeric objects using the ValueOf() DoubleVal=Double.ValueOf(str);

FloatVal=Float.ValueOf(str);

IntVal=Integer.ValueOf(str);

LongVal=Long.ValueOf(str);

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