Immutability of Strings in Java

Question

Consider the following example.

String str = new String();

str  = \"Hello\";
System.out.println(str);  //Prints Hello

str = \"Help!\";
System.out.println(s         


        

Answer 1

String in Java in Immutable and Final just mean it can't be changed or modified:

Case 1:

class TestClass{  
 public static void main(String args[]){  
   String str = "ABC";  
   str.concat("DEF");  
   System.out.println(str);  
 }  
} 

Output: ABC

Reason: The object reference str is not changed in fact a new object "DEF" is created which is in the pool and have no reference at all (i.e lost).

Case 2:

class TestClass{  
 public static void main(String args[]){  
   String str="ABC";  
   str=str.concat("DEF");  
   System.out.println(str);  
 }  
}  

Output: ABCDEF

Reason: In this case str is now referring to a new object "ABCDEF" hence it prints ABCDEF i.e. previous str object "ABC" is lost in pool with no reference.