Java read-only collections

Lightweight read-only collection wrappers for Java. Inspired by read-only interfaces from C#.

Usage example

import com.github.grzesiek_galezowski.collections.readonly.factory.ReadOnlyCollections;

//...

List<Integer> list = ...;
ReadOnlyList<Integer> readOnlyVersion = readOnly(list);
someone.doSomething(readOnlyVersion);

Read-only vs unmodifiable

• Unmodifiable collections contain modifying operations, but throw exceptions when they are invoked. Read-only collections do not contain modifying operations. In other words, unmodifiable exceptions prohibit change during runtime, while read-only collections prohibit change during compile time (but only to those that hold a read-only wrapper - holders of the original will be able to modify at will).

Read-only vs immutable (e.g. Vavr)

• Immutable collections contain methods such as add, but instead of modifying the data, they return new collection. Read-only collections do not directly contain such operations (although if someone wants, it can be achieved with streams). When someone is not used to immutable collections, they may invoke the add method believing that it modifies the collection state and ignoring the returned value (this is especially true of Vavr which has some collections named exactly like their java.util mutable counterparts).
• Immutable collections have the guarantee that they cannot change. A read-only collection is merely a view on a collection that can be changed by whoever holds the non-read-only reference.