09_String_Arrays_Vectors.pdf

Class String

java.lang.Object

java.lang.String

public final class String extends Object

•The String class represents character strings

How to Create String objects

String str = "abc";

char data[] = {'a', 'b', 'c'};

String str = new String(data);

String cde = "cde";

C lass String has method for

The class String includes methods for

• examining individual characters of the sequence

• comparing strings

• searching strings

• extracting substrings

• creating a copy of a string

char charAt(int index) Returns the char value at the specified index.

int

compareTo(String anotherString) Compares two strings lexicographically.

int

compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case differences.

String

concat(String str) Concatenates the specified string to the end of this string.

boolean

contentEquals(StringBuffer sb) Compares this string to the specified StringBuffer.

static String

copyValueOf(char[] data) Returns a String that represents the character sequence in the array specified.

static String

copyValueOf(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified.

boolean

endsWith(String suffix) Tests if this string ends with the specified suffix.

boolean equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case considerations.

int hashCode() Returns a hash code for this string.

int indexOf(int ch) Returns the index within this string of the first occurrence of the specified character.

int indexOf(int ch, int fromIndex) Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.

int indexOf(String str) Returns the index within this string of the first occurrence of the specified substring.

int indexOf(String str, int fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.

boolean isEmpty() Returns true if, and only if, length() is 0.

int lastIndexOf(int ch) Returns the index within this string of the last occurrence of the specified character.

int lastIndexOf(int ch, int fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward

int

lastIndexOf(String str) Returns the index within this string of the rightmost occurrence of the specified substring.

int

lastIndexOf(String str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring,

searching backward starting at the specified index. int length() Returns the length of this string.

char[] toCharArray() Converts this string to a new character array. String toLowerCase()

String

toString() This object (which is already a string!) is itself returned.

static String valueOf(boolean b) static String valueOf(char c)

static String valueOf(char[] data)

static String valueOf(char[] data, int offset, int count) static String valueOf(double d)

static String valueOf(float f) static String valueOf(int i) static String valueOf(long l)

static String

Substring

•

String Str=“abcdefgh”;

•

Str.subString(3);

•

Str.subString(2,4);

•

Str.subString(3,3)



cefgh

length or length()

String a[]={“a”,”b”};

a.length



2

indexOf()

String str=“Nihar ranjan roy”;

int i=str.indexOf(‘a’);

charAt()

String str=“Nihar”;

Char ch=str.charAt(2);

replace()replaces every occurrence of on character with another.

String lang=“english”;

equals() vs ==

“nihar”.equals(“nihar”); Or

String name=“nihar”; Name.equals(“nihar”);

equalsIgnoreCase()

equals compares for contents

==  compares for two object references, to see

Example

String s1=“java” String s2=“JAVA”;

toString()

Class Student {String name; int roll

}

Student Obj=new Student(); System.out.println(Obj) ;

 what is the output?;

Class Student {….

…..

public String toString() {

System.out.println(“Student@”+name+”@”+”roll”); }

StringBuffer

String class objects are immutable and with fixed length in contrast to StringBuffer class objects whose length can be varied and we can insert characters either in the middle or at the end

Constructor

StringBuffer() 16 char

StringBuffer(int i)

Principal methods

•

append

•

insert

•

length

•

capacity

•

reverse

StringBuffer name=new

StringBuffer(“Nihar”); name.append(“ Roy”);

Append example

class StrBuffer {

public static void main(String args[]) {

StringBuffer str=new StringBuffer(10); str.append("India is");

System.out.println(str);

System.out.println(str.length()); System.out.println(str.capacity()); str.append("a beautiful country"); System.out.println(str.length()); System.out.println(str.capacity()); }

Arrays

Collection of elements of the same type

that are referred by a common name.

int arr=new int[5];



All initialise with default value

MultiDimensional

int arr[][]=new int[4][4];

Initialisation



Arr[0][0]=45;

Arr[0][1]=34;

….

Or

Vector

package import java.util.*;

It permits to store different elements that are of different class.

• Vector in also an expandable array of objects

• Array can be either increased of decreased after

some its elements have been deleted

• We cannot use simple data types in vector

• Vector automatically increased its size when

Constructor

Vector()

Vector(int size)

Vector(int size, int increment)



The value is incremented whenever it

Methods in Vector class

addElement()at the last position

elementAt(int i)returns element at that position

Size()no of objects present

Capacityno of spaces allocated

removeElement(Object o)removes the first

occurrence of the object o in the vectore if and only if it is found

How to add primitive data types

Vector v=new Vector(2,4);

v.addElement(new Integer(1200));

v.addElement(new Character(‘N’));

v.addElement(new Boolen(true));