Why String objects are immutable in java?

Question

It is often the case that programmers would want to manipulate String objects. The way String objects in java work is that it creates a new object every time a String is manipulated. This is very time consuming. I know there is a Stringbuffer class that allows for mutable strings but I am trying to understand why Java suggests that Strings should be immutable? and is this a common thing among other programming/scripting languages as well?

Answer 1

Here is a nice article on the advantages of using immutable object in general http://www.javapractices.com/topic/TopicAction.do?Id=29

Benefits of using immutable object:

• are simple to construct, test, and use
• are automatically thread-safe and have no synchronization issues
• don't need a copy constructor
• don't need an implementation of clone
• allow hashCode to use lazy initialization, and to cache its return value
• don't need to be copied defensively when used as a field
• make good Map keys and Set elements (these objects must not change state while in the collection)
• have their class invariant established once upon construction, and it never needs to be checked again
• always have "failure atomicity" (a term used by Joshua Bloch): if an immutable object throws an exception, it's never left in an undesirable or indeterminate state

Answer 2

In languages immutability has several useful advantages. They can be freely shared; no copying overhead, etc. An immutable object has exactly one state. Many other languages (such as Python, C#) use immutable strings.