immutability

Is there an immutable alternative to the primitive arrays in Java? Making a primitive array final doesn't actually prevent one from doing something like final int[] array = new int[] {0, 1, 2, 3}; array[0] = 42; I want the elements of the array to be unchangeable. Not with primitive arrays. You'll need to use a List or some other data structure: List<Integer> items = Collections.unmodifiableList(Arrays.asList(0,1,2,3)); ColinD My recommendation is to not use an array or an unmodifiableList but to use Guava 's ImmutableList , which exists for this purpose. ImmutableList<Integer> values =

Although I have never needed this, it just struck me that making an immutable object in Python could be slightly tricky. You can't just override __setattr__ , because then you can't even set attributes in the __init__ . Subclassing a tuple is a trick that works: class Immutable(tuple): def __new__(cls, a, b): return tuple.__new__(cls, (a, b)) @property def a(self): return self[0] @property def b(self): return self[1] def __str__(self): return "<Immutable {0}, {1}>".format(self.a, self.b) def __setattr__(self, *ignored): raise NotImplementedError def __delattr__(self, *ignored): raise

We all know that String is immutable in Java, but check the following code: String s1 = "Hello World"; String s2 = "Hello World"; String s3 = s1.substring(6); System.out.println(s1); // Hello World System.out.println(s2); // Hello World System.out.println(s3); // World Field field = String.class.getDeclaredField("value"); field.setAccessible(true); char[] value = (char[])field.get(s1); value[6] = 'J'; value[7] = 'a'; value[8] = 'v'; value[9] = 'a'; value[10] = '!'; System.out.println(s1); // Hello Java! System.out.println(s2); // Hello Java! System.out.println(s3); // World Why does this