String Class
A String is a series of
characters and is different from any array of characters. It is an object which implies once a string
is created, we can not change it. This
makes the strings to be constant. Objects
of string class can not grow once they are created. The ‘+’ operator is used to join two strings
together.
String Literals
String literals are created, by
specifying characters in double quotes.
They are called literals because their value is constant and can not
change. For example:
String name = “P. Pandit”;
String Pool
Whenever a string is created,
internally it is treated as an instance of a String. A Java program can contain many string
literals. Hence it holds a String Pool that represents all the
literals created in the program.
Whenever a string literal is created, the String Pool is searched to see
if it exists. If the string literal is
exists, new instance is not created for that String Pool. Here an existing instance is assigned to the
new string. This saves lot of memory
space. For example:
String day = “Monday”;
String weekday = “Monday”;
Here an instance for the day
whose value is Monday is created in the String Pool. When the variable named weekday is created
holding same value as the variable day, an existing instance is assigned to the
variable weekday. So both day and
weekday point to the same string in the String Pool.
Example 1( String Concat)
class StringCon
{
public static void main(String
ars[])
{
String A = new
String("Sandhyashree");
String B = new
String("Sports");
String C = new
String("Leena's ");
String D = new String("Software");
System.out.println("
");
System.out.println("String
Before Concatenation without + Operator");
System.out.println(A);
System.out.println(B);
System.out.println("
");
A = A+ " " +B;
System.out.println("String
After Concatenation with + Operator");
System.out.println(A);
System.out.println("
");
System.out.println("String
Before Concatenation without Concat Function");
System.out.println(C);
System.out.println(D);
System.out.println("
");
System.out.println("String
After Concatenation with Concat Function");
C=C.concat(D);
System.out.println("
");
System.out.println(C);
}
}
Example 2(String Constructor)
class StringCons {
public static void main(String
ars[]) {
String str1 = new String( );
String str2 = new
String("Hello Guies");
char ch[] = {'A','B','C','D','E'};
String str3 = new String(ch);
String str4 = new String(ch,0,2);
System.out.println(str1);
System.out.println("
");
System.out.println(str2);
System.out.println("
");
System.out.println(str3);
System.out.println("
");
System.out.println(str4);
}
}
String class methods
String class provides different
methods. The methods are divided as
follows:
Return_type Method name (parameters) Set 1
Ø
char charAt(int
index)
Ø
boolean endsWith(String
suffix)
Ø
boolean startsWith(String
suffix)
Ø
int length(
)
Example 3(String Method 1 )
class StringMethod{
public static void main(String
ars[]){
String name = new
String("Anand Infotec");
char ch = name.charAt(5);
System.out.println("character
at 5 th Index is "+ch);
int length=name.length( );
System.out.println("
");
System.out.println("Length
of name is "+length);
if(name.startsWith("Anand")) {
System.out.println("Name
starts with Anand");
}
if(name.endsWith("Infotec")){
System.out.println("Name
ends with Infotec ");
}
}
}
Return_type Method name (parameters) Set 2
Ø
String copyValueOf(char
ch[ ], int start_index, int count)
Ø
String copyValueOf(char
ch [ ] )
Ø
char [ ] toCharArray(
)
Return_type Method name (parameters) Set 3
Ø
int indexOf(char
ch)
Ø
int indexOf(char
ch, int startindex)
Ø
int indexOf(String
str)
Ø
int indexOf(String
str, int startindex)
Return_type Method name (parameters) Set 4
Ø
int lastindexOf(char
ch)
Ø
int lastindexOf(char
ch, int startindex)
Ø
int lastindexOf(String
str)
Ø
int lastindexOf(String
str, int startindex)
Return_type Method name (parameters) Set 5
Ø
boolean equals(Object
ob)
Ø
String toUpperCase(String)
Ø
String toLowerCase(String)
Ø
String trim(
)
Return_type Method name (parameters) Set 6
Ø
String substring(int
index)
Ø
String substring(int
startindex, int endindex)
Ø
String valueOf(double)
Ø
String valueOf(Boolean)
Ø
String valueOf(char)
StringBuffer class
The String class is used to
support operations on strings of characters.
The String class supports constant strings. Often it so happens that, strings have to be
modified. That is insertions/deletions might
be necessary in some part of the strings.
This can not be done or handled by the String class, but by the
StringBuffer class. StringBuffer class
provides various methods to manipulate string object. StringBuffer class supports growable,
modifiable strings.
Thus objects of StringBuffer
class are expandable and flexible.
Characters of strings can be inserted in between in the StringBuffer
object as well as they can be appended at the end. The various StringBuffer methods are as
follows:-
Set 1
Ø
StringBuffer append(String str)
Ø
StringBuffer append(char ch [ ] )
Ø
StringBuffer append(char ch [ ], int
offset, int length)
Ø
StringBuffer append(int no)
Example 4(String Buffer
Constructor)
class StringBuffCons{
public static void main(String
ars[]){
StringBuffer s1 = new
StringBuffer( );
StringBuffer s2 = new
StringBuffer(20);
StringBuffer s3 = new
StringBuffer("String Buffers");
StringBuffer s4 = new
StringBuffer(5);
System.out.println("s3 =
" +s3);
System.out.println("length
of s2 "+s2.length( ));
System.out.println("length
of s3 "+s3.length( ));
System.out.println("capacity
of s1 "+s1.capacity( ));
System.out.println("capacity
of s2 "+s2.capacity( ));
System.out.println("capacity
of s3 "+s3.capacity( ));
System.out.println("capacity
of buffer s4 "+s4.capacity( ));
s4.ensureCapacity(8);
System.out.println("capacity
of buffer s4 "+s4.capacity( ));
s4.ensureCapacity(30);
System.out.println("capacity
of buffer s4 "+s4.capacity( ));
}
}
Set 2
Ø
StringBuffer insert(int insertposition, String str)
Ø
StringBuffer insert(int insertposition, char ch)
Ø
StringBuffer insert(int insertposition, float f)
Set 3
Ø
char charAt(int
index)
Ø
void setCharAt(int
index, char ch)
Ø
void getChars(int
begin, int end, char destination[ ], int begin)
Ø
void setLength(int
length)
Set 4
Ø
StringBuffer reverse( )
Practical Examples
Example 1(String Methods1)
class StringMethods1
{
public static void main(String
ars[]){
char name[] =
{'A','n','a','n','d','I','n','f','o','t','e','c'};
String
subname=String.copyValueOf(name,5,3);
System.out.println(subname);
String
fullname=String.copyValueOf(name);
System.out.println(fullname);
String text = new
String("Hello World");
char
textArray[]=text.toCharArray( );
for(int i=6;i<text.length(
);i++)
System.out.print(textArray[i]+"\t");
}
}
Example 2(String Methodss2)
class StringMethods2 {
public static void main(String
args[]) {
String day = new
String("Sunday");
int index1 = day.indexOf('n');
System.out.println("Index of
Character 'n' " +index1);
int index2 = day.indexOf('n',3);
if(index2==-1)
System.out.println("Index of
Character 'n' not found");
int index3 =
day.indexOf("Sun");
System.out.println("Index of
String Sun is "+index3);
int index4 =
day.indexOf("day");
System.out.println("Index of
String day from specified index is "+index4);
String day1 = new String("Sunday
Monday");
int index5 =
day1.lastIndexOf('n');
System.out.println("Last
Index of Character 'n' " +index5);
int index6 =
day1.lastIndexOf('n',7);
if(index6==-1)
System.out.println("Last
Index of Character 'n' not found");
else
System.out.println("Last
Index of Character 'n' " +index6);
int index7 =
day1.lastIndexOf("ay");
System.out.println("Last
Index of String ay is "+index7);
int index8 =
day1.lastIndexOf("day",6);
System.out.println("Index of
Character day from specified index is " +index8);
}
}
Example 3(String Methodss3)
class StringMethod3{
public static void main(String
args[]){
String lower = new
String("good morning");
System.out.println(lower
+"in Upper Case : "+lower.toUpperCase( ));
String upper = new
String("Sandhyashree");
System.out.println(upper
+"in Lower Case : "+upper.toLowerCase( ));
String spaces = new
String(" Spaces ");
System.out.println(spaces
+"after Trimming : "+spaces.trim( ));
String text1 = new
String("TEXT");
String text2 = new
String("TEXT");
if (text1.equals(text2))
System.out.println("Text 1
and Text2 are Equal ");
System.out.println("
");
String text3 = new
String("An Apple a Day keeps Doctor Away");
String sub1 =
text3.substring(text3.indexOf('k'));
System.out.println(sub1);
String sub2 = text3.substring(3,8);
System.out.println(sub2);
System.out.println(String.valueOf(45.00));
System.out.println(String.valueOf(true));
System.out.println(String.valueOf('$'));
String replacedStr =
text3.replace(' ','*');
System.out.println(replacedStr);
}
}
Example 4(String Buffer Method1)
import java.awt.*;
class StringBuffMethod1{
public static void main(String
args[]){
StringBuffer s1= new
StringBuffer("Microsoft");
System.out.println("s1
before append " +s1);
System.out.println("s1 after
append " );
s1.append("Windows XP");
System.out.println("s1
"+s1 );
char ch[]={'
','C','l','a','s','s'};
char
ch1[]={'O','n','e','E','x','a','m','p','l','e'};
s1.append(ch);
System.out.println("s1
"+s1 );
s1.append(ch,0,1);
s1.append(ch1,3,7);
System.out.println("s1
"+s1 );
s1.append(1);
System.out.println("s1
"+s1 );
}
}
Example 5(String Buffer Method2)
import java.awt.*;
class StringBuffMethod2{
public static void main(String
args[]){
StringBuffer s1= new
StringBuffer("Java sion");
System.out.println("s1
before append " +s1);
System.out.println("s1 after
append " );
s1.insert(5,"Ver");
System.out.println("s1
"+s1 );
s1.append(" For You");
System.out.println("s1
"+s1 );
s1.insert(13,1.2);
System.out.println("s1
"+s1 );
s1.insert(16,' ');
System.out.println("s1
"+s1 );
}
}
Example 6(String Buffer Method3)
import java.awt.*;
class StringBuffMethod3{
public static void main(String
args[]){
String name="James Gosling -
Inventor of Java";
StringBuffer s1= new StringBuffer
(name);
if(s1.charAt(14)=='-')
s1.setCharAt(14,':');
System.out.println("s1
"+s1 );
char ch[] = new char[14];
s1.getChars(0,13,ch,0);
System.out.println("New
array is " +String.valueOf(ch));
s1.setLength(s1.length( )+10);
System.out.println("s1
"+s1 );
s1.setLength(5);
System.out.println("s1
"+s1 );
}
}
Example 7(String Buffer Reverse
Method)
import java.awt.*;
class reverseString{
public static void main(String
args[]){
System.out.println("Original
String Reversed String");
for(int i
=0;i<args.length;i++){
StringBuffer str = new
StringBuffer(args[i]);
System.out.println(" "+args[i]+"\t\t\t"+
" "+str.reverse( ));
}
}
}
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