Why is String Immutable

  1. Immutable – Unchangeable. Once initialized the values cannot be changed
  2. When tried to change it will create a new object
    1. String s= new String( ” Zoo “) ;s = s + “Keeper”;  The JVM will create 2 objects on the heap.  Once to store “Zoo” and another to store “Zoo Keeper”
  3. Primitive datatypes like int,long etc can also be made immutable by declaring it “final”
  4. They are thread-safe implicitly. Since threads cannot change the value no need to perform synchronization.
  5. Suitable to act as a “key” to HashMap  etc
  6. Immutable class can be created by
    1. Declaring the class final
    2. Or Use Static and define private Constructor
    3. Do not provide any method for changing the state of the object
  7. Hashcode of the String will always be the same and hence it can cached
  8. Strings are used in DB connection , Networking etc. If it is not mutable then it would lead to serious issue not connecting to the right DB etc
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