String handling in java

String Handling

The basic aim of String Handling concept is storing the string data in the main memory (RAM), manipulating the data of the string, retrieving the part of the String etc. String Handling provides a lot of concepts that can be performed on a string such as concatenation of string, comparison of string, find sub string etc.

Character

It is an identifier enclosed within single quotes (‘ ‘).
Example: ‘A’, ‘$’, ‘p’

String:

String is a sequence of characters enclosed within double quotes (” “) is known as String.
Example: “Java Programming”.

In java programming to store the character data we have a fundamental datatype called char. Similarly to store the string data and to perform various operation on String data, we have three predefined classes they are:

  1. String
  2. StringBuffer
  3. StringBuilder

 

1. String class

It is a predefined class in java.lang package can be used to handle the String. String class isimmutable that means whose content cannot be changed at the time of execution of program.

String class object is immutable that means when we create an object of String class it never changes in the existing object.
Example:

class StringHandling

{

public static void main(String arg[])

{

String s=new String("java"); 

s.concat("software");

System.out.println(s);

}

}

Output

java

Explanation: Here we cannot change the object of String class so output is only java not java software.

 

Methods of String class

A. length()

length(): This method is used to get the number of character of any string.

class StringHandling

{

public static void main(String arg[])

{

int l;

String s=new String("Java"); 

l=s.length();

System.out.println("Length: "+l);

}

}

Output

Length: 4

B. charAt(index)

charAt(): This method is used to get the character at a given index value.

class StringHandling

{

public static void main(String arg[])

{

char c;

String s=new String("Java"); 

c=s.charAt(2);

System.out.println("Character: "+c);

}

}

Output

Character: v

C. toUpperCase()

toUpperCase(): This method is use to convert lower case string into upper case.

class StringHandling

{

public static void main(String arg[])

{

String s="Java"; 

System.out.println("String: "+s.toUpperCase());

}

}

Output

String: JAVA

D. toLowerCase()

toLowerCase(): This method is used to convert lower case string into upper case.

class StringHandling

{

public static void main(String arg[])

{

String s="JAVA"; 

System.out.println("String: "+s.toLowerCase());

}

}

Output

String: java

E. concat()

concat(): This method is used to combined two string.

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="Raddy"; 

System.out.println("Combined String: "+s1.concat(s2));

}

}

Output

Combined String: HiteshRaddy

F. equals()

equals(): This method is used to compare two strings, It return true if strings are same otherwise return false. It is case sensitive method.

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="Raddy"; 

String s3="Hitesh";

System.out.println("Compare String: "+s1.equals(s2));

System.out.println("Compare String: "+s1.equals(s3));

}

}

Output

Compare String: false

Compare String: true

G. equalsIgnoreCase()

equalsIgnoreCase(): This method is case insensitive method, It return true if the contents of both strings are same otherwise false.

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="HITESH"; 

String s3="Raddy";

System.out.println("Compare String: "+s1.equalsIgnoreCase(s2));

System.out.println("Compare String: "+s1.equalsIgnoreCase(s3));

}

}

Output

Compare String: true

Compare String: false

H. compareTo()

compareTo(): This method is used to compare two strings by taking unicode values, It return 0 if the string are same otherwise return +ve or -ve integer values.

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="Raddy";

int i;

i=s1.compareTo(s2);

if(i==0)

{

System.out.println("Strings are same");

}

else

{

System.out.println("Strings are not same");

}

}

}

Output

Strings are not same

I. compareToIgnoreCase()

compareToIgnoreCase(): This method is case insensitive method, which is used to compare two strings similar to compareTo().

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="HITESH";

int i;

i=s1.compareToIgnoreCase(s2);

if(i==0)

{

System.out.println("Strings are same");

}

else

{

System.out.println("Strings are not same");

}

}

}

Output

Strings are same

J. startsWith()

startsWith(): This method return true if string is start with given another string, otherwise it returns false.

class StringHandling

{

public static void main(String arg[])

{

String s="Java is programming language";

System.out.println(s.startsWith("Java"));

}

}

Output

true

K. endsWith()

endsWith(): This method return true if string is end with given another string, otherwise it returns false.

class StringHandling

{

public static void main(String arg[])

{

String s="Java is programming language";

System.out.println(s.endsWith("language"));

}

}

Output

true

L. subString()

subString(): This method is used to get the part of given string.

Example 1:

class StringHandling

{

public static void main(String arg[])

{

String s="Java is programming language";

System.out.println(s.substring(8)); // 8 is starting index

}

}

Output

programming language

 

Example 2:

class StringHandling

{

public static void main(String arg[])

{

String s="Java is programming language";

System.out.println(s.substring(8, 12));

}

}

Output

prog

M. indexOf()

indexOf(): This method is used find the index value of given string. It always gives starting index value of first occurrence of string.

class StringHandling

{

public static void main(String arg[])

{

String s="Java is programming language";

System.out.println(s.indexOf("programming"));

}

}

Output

8

N. lastIndexOf()

lastIndexOf(): This method used to return the starting index value of last occurence of the given string.

class StringHandling

{

public static void main(String arg[])

{

String s1="Java is programming language";

String s2="Java is good programming language";

System.out.println(s1.lastIndexOf("programming"));

System.out.println(s2.lastIndexOf("programming"));

}

}

Output

8

13

O. trim()

trim(): This method remove space which are available before starting of string and after ending of string.

class StringHandling

{

public static void main(String arg[])

{

String s="    Java is programming language    ";

System.out.println(s.trim());

}

}

Output

Java is programming language

P. split()

split(): This method is used to divide the given string into number of parts based on delimiter (special symbols like @ space , ).

class StringHandling

{

public static void main(String arg[])

{

String s="java@outlook.com";

String[] s1=s.split("@");  // divide string based on @

for(String c:s1) //  foreach loop 

{

System.out.println(c); 

}

}

}

Output

java

@outlook.com

Q. replace()

replace(): This method is used to return a duplicate string by replacing old character with new character.

Note: In this method data of original string will never be modify.

class StringHandling

{

public static void main(String arg[])

{

String s1="java";

String s2=s1.replace('j', 'k');

System.out.println(s2);

}

}

Output

kava

2. StringBuffer

It is a predefined class in java.lang package can be used to handle the String, whose object is mutable that means content can be modify. 
StringBuffer class is working with thread safe mechanism that means multiple thread are not allowed simultaneously to perform operation of StringBuffer.

StringBuffer class object is mutable that means when we create an object of StringBulder class it can be change.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("java");

sb.append("software");

System.out.println(sb);

}

}

Output

javasoftware

Explanation: Here we can changes in the existing object of StringBuffer class so output is javasoftware.

Difference between String and StringBuffer

  String StringBuffer
1 The data which enclosed within double quote (” “) is by default treated as String class. The data which enclosed within double quote (” “) is not by default treated as StringBuffer class
2 String class object is immutable StringBuffer class object is mutable
3 When we create an object of String class by default no additional character memory space is created. When we create an object of StringBuffer class by default we get 16 additional character memory space.

Similarities between String and StringBuffer

  • Both of them are belongs to public final, so that they never participates in inheritance that is is-A relationship is not possible but they can always participates in As-A and Uses-A relationship.
  • We cannot override the method of String and StringBuffer.

Methods of StringBuffer class

A. reverse()

reverse(): This method is used to reverse the given string and also the new value is replaced by the old string.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("java code");

System.out.println(sb.reverse());

}

}

Output

edoc avaj

B. insert()

insert(): This method is used to insert either string or character or integer or real constant or boolean value at a specific index value of given string.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("this is my java code");

System.out.println(sb.insert(11, "first "));

}

}

Output

this is my first java code

C. append()

append(): This method is used to add the new string at the end of original string.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("java is easy");

System.out.println(sb.append(" to learn"));

}

}

Output

java is easy to learn

D. replace()

replace() This method is used to replace any old string with new string based on index value.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("This is my code");

System.out.println(sb.replace(8, 10, "java"));

}

}

Output

This is java code

Explanation: In above example java string is replaced with old string (my) which is available between 8 to 10 index value.

E. deleteCharAt()

deleteCharAt(): This method is used to delete a character at given index value.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("java");

System.out.println(sb.deleteCharAt(3));

}

}

Output

java

F. delete()

delete(): This method is used to delete string form given string based on index value.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("java is easy to learn");

StringBuffer s;

s=sb.delete(8, 13);

System.out.println(sb);

}

}

Output

java is to learn

Explanation: In above example string will be deleted which is existing between 8 and 13 index value.

G. toString()

toString(): This method is used to convert mutable string value into immutable string.

Example

class StringHandling

{

public static void main(String arg[])

{

StringBuffer sb=new StringBuffer("java");

String s=sb.toString();

System.out.println(s);

s.concat("code");

}

}

Output

java

 

String Compare

There are three way to compare string object in java:

  • By equals() method
  • By == operator
  • By compreTo() method

By equals() method

equals() method always used to comparing contents of both source and destination String. It return true if both string are same in meaning and case otherwise it returns false. It is case sensitive method.

 

Example

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="Raddy";

String s3="Hitesh";

System.out.println("Compare String: "+s1.equals(s2));

System.out.println("Compare String: "+s1.equals(s3));

}

}

Output

Compare String: false

Compare String: true

By == Operator

== Operator is always used for comparing references of both source and destination objects but not their contents.

 

Example

class StringHandling

{

public static void main(String arg[])

{

String s1=new String("java");

String s2=new String("java");

if(s1==s2)

{

System.out.println("Strings are same");

}

else

{

System.out.println("Strings are not same");

}

}

}

Output

Strings are not same

compareTo()

comapreTo() method can be used to compare two string by taking Unicode values. It returns 0 if the string are same otherwise returns either +ve or -ve integer.

Example

class StringHandling

{

public static void main(String arg[])

{

String s1="Hitesh";

String s2="Raddy";

int i;

i=s1.compareTo(s2);

if(i==0)

{

System.out.println("Strings are same");

}

else

{

System.out.println("Strings are not same");

}

}

}

Output

Strings are not same

Difference between equals() method and == operator

equals() method always used to comparing contents of both source and destination String.

== Operator is always used for comparing references of both source and destination objects but not their contents.

 

String Concatenation

There are two way to concat string object in java:

·         By + (string concatenation) operator

·         By concat() method

By + operator

Using Java string concatenation operator (+) you can combined two or more strings.

Example

class StringHandling

{

public static void main(String arg[])

{

String s= "Java" + "Code";

System.out.println(s);

}

}

Output

JavaCode

By concat() method

concat() method is used to combined two strings.

Example

class StringHandling

{

public static void main(String arg[])

{

String s1="Java";

String s2="Code";

String s3=s1.concat(s2);

System.out.println(s3);

}

}

Output

JavaCode

 

3. StringBuilder

It is a predefined class in java.lang package can be used to handle the String. StringBuilder class is almost similar to to StringBuffer class. It is also a mutable object.
The main difference StringBuffer and StringBuilder class is StringBuffer is thread safe that means only one threads allowed at a time to work on the String whereas StringBuilder is not thread safe that means multiple threads can work on same String value.

Difference between StringBuffer and StringBuilder

All the things between StringBuffer and StringBuilder are same only difference is StringBuffer is synchronized and StringBuilder is not synchronized. Synchronized means one thread is allow at a time so it thread safe. Not synchronized means multiple threads are allow at a time so it not thread safe.

  StringBuffer StringBuilder
1 It is thread safe. It is not thread safe.
2 Its methods are synchronized and provide thread safety. Its methods are not synchronized and unable to provide thread safety.
3 Relatively performance is low because thread need to wait until previous process is complete. Relatively performance is high because no need to wait any thread it allows multiple thread at a time.
1 Introduced in 1.0 version. Introduced in 1.5 version.

When we use String, StringBuffer and StringBuilder

  • If the content is fixed and would not change frequently then we use String.
  • If content is not fixed and keep on changing but thread safety is required then we use StringBuffer
  • If content is not fixed and keep on changing and thread safety is not required then we use StringBuilder

 

 

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