String of Java

• String  is immutable in Java. An immutable class is simply a class whose instances cannot be modified. All information in an instance is initialized when the instance is created and the information can not be modified. In  fact none  of methods defined in the String class modify  the object's own value . They all create new String objects.

                            ex :-    String   newString  =  "Game" ;
                                       newString.replace('a', 'A');
                                       System.out.println(newString) ; // Will print Game  
 
                 Due to strings  are immutable  we  can achieve

• Security             - String is widely used as a parameter for many java classes, e.g. network connection, opening files, etc. Were String not immutable, a connection or file would be changed and this can lead to a serious security threat. The method thought it was connecting to one machine, but was not. Mutable strings could cause a security problem in Reflection too, as the parameters are strings.
• Safe in threads   - immutable objects can not be changed, they can be shared among multiple threads freely.

           

•  String Pool  -  When  string  is  created  and  if  the  string already existing in the  pool  without  using  key  word  new  ,then reference of  existing  string will  be  return , instead of  creating  new object.  

  ex :-   String  newStingOne =  "ABAC" ;

            String  newStingTwo =  "ABAC" ;  

  Above code will create only one string object in the heap.

• If a string is going to remain constant throughout the program, then use String class object because a String object is immutable.                                                                                                                                                                     You should use StringBuilder class when we  have larger strings or modifying the  contents of a string  often .Doing that will  increase   performance.If a string can change (example: lots of logic and operations in the construction of the string) and will only be accessed from a single thread, using a StringBuilder is good enough.                                 If a string can change, and will be accessed from multiple threads, use a StringBuffer because StringBuffer is synchronous so you have thread-safety.
• Class StringBuffer  provides  same functionality  StringBuilder  provides  minus the additional feature of synchronized methods
  
  
  
  
  
  References Used  :-  why-string-is-immutable-in-java
                               :-   OCA Java SE 8  Programer  1 Guide  by   Mala Gupta