Difference Between String , StringBuilder And StringBuffer Classes With Example : Java

Today we are going to understand the difference between String
, StringBuilder and StringBuffer . As you will find that there are minor differences between the above mentioned classes.

String

String is immutable  (
once created can not be changed )object  . The object created as a String is stored in the  Constant String Pool 
. 
Every immutable object in Java is thread safe ,that implies String is also thread safe . String can not be used by two threads simultaneously.
String  once assigned can not be changed.

String  demo = " hello " ;
// The above object is stored in constant string pool and its value can not be modified.

demo="Bye" ;     //new "Bye" string is created in constant pool and referenced by the demo variable            
 // "hello" string still exists in string constant pool and its value is not overrided but we lost reference to the  "hello"string  

StringBuffer

StringBuffer is
mutable means one can change the value of the object . The object created through StringBuffer is stored in the heap . StringBuffer  has the same methods as the StringBuilder , but each
method in StringBuffer is synchronizedthat is StringBuffer
is thread safe . 

Due to this it does not allow  two threads to simultaneously access the same method . Each method can be accessed by one thread at a time .

But being thread safe has disadvantages too as the performance of the StringBuffer hits due to thread safe property . Thus  StringBuilder is faster than the
StringBuffer when calling the same methods of each class.

StringBuffer value can be changed , it means it can be assigned to the new value . Nowadays its a most common interview question ,the differences between the
above classes .
String Buffer can be converted to the string by using 
toString()
method.

StringBuffer demo1 = new StringBuffer("Hello") ;
// The above object stored in heap and its value can be changed .

demo1=new StringBuffer("Bye");
// Above statement is right as it modifies the value which is allowed in the StringBuffer

StringBuilder

StringBuilder  is same as the StringBuffer , that is it stores the object in heap and it can also be modified . The main difference between the StringBuffer
and StringBuilder is that StringBuilder is also not thread safe. 
StringBuilder is fast as it is not thread safe .  

StringBuilder demo2= new StringBuilder("Hello");
// The above object too is stored in the heap and its value can be modified
demo2=new StringBuilder("Bye"); 
// Above statement is right as it modifies the value which is allowed in the StringBuilder

----------------------------------------------------------------------------------------------------
                                    String
                   StringBuffer  
      StringBuilder
----------------------------------------------------------------------------------------------------           
Storage Area | Constant String Pool          
Heap                       Heap 
Modifiable     |  No (immutable)            Yes(
mutable )          Yes( mutable )
Thread Safe   |           Yes                
                 Yes                              No
 Performance |         Fast                  
             Very slow                    Fast
---------------------------------------------------------------------------------------------------

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