In the given example only one object will be created. Firstly JVM will not find any string object with the value “Welcome” in the string

Outline
▪ What is string ?
▪ How to createString object?
▪ Some important operations of strings
▪ Some important string class methods
▪ StringBuffer class & StringBuilder class
▪ Difference between String andStringBuffer
▪ Difference between StringBuffer andStringBuilder

What is String ?
▪ Strings, which are widely used in Java
programming, are a sequence of characters. In
Java programming language, strings are
treated as objects.
▪ The Java platform provides the String class to
create and manipulate strings.

Important Notes about String
▪ String – Object or Primitive?
- Strings could be considered a primitive type in Java, but in fact they are not.
As a String is actually made up of an array of char primitives.
▪ String objects are immutable!
-That means once a string object is created it cannot be altered. For mutable
string, you can use StringBuffer and StringBuilder classes.
[An object whose state cannot be changed after it is created is known as an
Immutable object. String, Integer, Byte, Short, Float, Double and all other wrapper
class's objects are immutable.]

How to createString object?
There are two ways to createString object:
1.By string literal
For Example:
String s="welcome";
2.By new keyword
For Example:
String s=newString("Welcome");

Java String Example
Output :
java
strings
example

Some important operations of strings
▪ StringConcatenation
▪ StringComparison
▪ Substring
▪ Length ofString etc.

String Concatenation
▪ There are 2 methods to concatenate two or more string.
Concatenate
two or more
string.
Using
concat()
method
Using +
operator

String Comparison
▪ String comparison can be done in 3 ways.
String
Comparison
Using
equals()
method
Using ==
operator
By
CompareTo()
method

Substring in Java
▪ A part of string is called substring. In other words, substring is a subset of another string.
▪ We can get substring from the given string object by one of the two methods:
1. publicString substring(int startIndex):
2. publicString substring(int startIndex, int endIndex):

Length of String
finds the length of the string. It returns count of total
▪ The java string length() method
number of characters.

Some more string class methods
▪ The java.lang.String class provides a lot of methods to work on string. By the help of
these methods, we can perform operations on strings.
▪ Here we will learn about the following methods :
1. charAt()
2. contains()
3. getChars()
4. indexOf()
5. replace()
6. toCharArray()
7. toLowerCase()
8. toUpperCase()

charAt() & contains()
 charAt() = returns a char value at the given index number.The index number starts from 0.
 contains() = searches the sequence of characters in this string. It returns true if sequence of char values
are found in this string otherwise returns false.

getChars()
 getChars() = copies the content of this string into specified char array.There are 4
arguments passed in getChars() method. It throws StringIndexOutOfBoundsException
if beginIndex is greater than endIndex.

indexOf()
 indexOf() = returns index
of given character value
or substring. If it is not
found, it returns -1. The
index counter starts from
zero.

replace()
 replace() = returns a string replacing all the old char orCharSequence to new char or
CharSequence.

toCharArray()
 toCharArray() = converts this string into character array.

toLowerCase() & toUpperCase()
 toLowerCase() = returns the string in lowercase letter. In other words, it converts all
characters of the string into lower case letter.
 toUpperCase() =returns the string in uppercase letter. In other words, it converts all
characters of the string into upper case letter.

Java StringBuffer class
▪ Java StringBuffer class is used to created mutable (modifiable) string.
▪ ImportantConstructors of StringBuffer class:
 StringBuffer(): creates an empty string buffer with the initial capacity of 16.
 StringBuffer(String str): creates a string buffer with the specified string.
 StringBuffer(int capacity): creates an empty string buffer with the specified capacity as length.
▪ Important methods of StringBuffer class:
 append(String s): is used to append the specified string with this string.The append() method is
overloaded like append(char), append(boolean), append(int), append(float), append(double) etc.
 insert(int offset, String s): is used to insert the specified string with this string at the specified position.
The insert() method is overloaded like insert(int, char), insert(int, boolean), insert(int, int), insert(int,
float), insert(int, double) etc.
 replace(int startIndex, int endIndex,String str): is used to replace the string from specified startIndex
and endIndex.
 delete(int startIndex, int endIndex): is used to delete the string from specified startIndex and endIndex.
 reverse(): is used to reverse the string.
 capacity(): is used to return the current capacity.

Java StringBuilder class
▪ Java StringBuilder class is used to create mutable (modifiable)
string.TheJavaStringBuilder class is same as StringBuffer class
except that it is non-synchronized.

Example of using StringBuffer & StringBuilder class

Difference between String and StringBuffer
No. String StringBuffer
1) String class is immutable. StringBuffer class is mutable.
2) String is slow and consumes more memory when
you concat too many strings because every time
it creates new instance.
StringBuffer is fast and consumes less memory
when you cancat strings.
3) String class overrides the equals() method of
Object class. So you can compare the contents of
two strings by equals() method.
StringBuffer class doesn't override the equals()
method of Object class.

Difference between StringBuffer and StringBuilder
No. StringBuffer StringBuilder
1) StringBuffer is synchronized i.e. thread safe. It
means two threads can't call the methods of
StringBuffer simultaneously.
StringBuilder is non-synchronized i.e. not
thread safe. It means two threads can call the
methods of StringBuilder simultaneously.
2) StringBuffer is less efficient thanStringBuilder. StringBuilder
StringBuffer.
is more efficient than

In the given example only one object will be created. Firstly JVM will not find any string object with the value “Welcome” in the string

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