Why string is immutable or final in java? What are the benefits of immutable object?

security reasons:

for opening network connections,you can pass host name,url as string

you can open any file in java by passing name of file as argument to File I/O classes.if string is not immutable this would lead serious security threat , I mean some one can access to any file for which he has authorization, and then can change the file name either deliberately or accidentally and gain access of those file.

Some of the important reasons are:

1. Security: for example, openning a file by name takes string argument for the file name. If string is not immutable, a person who has access to a certain file name, can gain access to other files by changing the name string.
2. Immutable objects are simple since they only have1 state to represent.
3. Immutable object are thread-safe inherintly, so they don't nead synchornization in multi-threaded programs