Do autoboxing and unboxing behave differently in Java and C#
autoboxing, c#, java
Solution
In your C# example there is no boxing or unboxing (and autoboxing) happening. `double` is just an alias for the `struct` `Double`.
In Java, the boxing is necessary. Because of type erasure, you can't create a `List<double>`, only `List<Double>`. At compile time, `List<?>` becomes `List<Object>` and boxing/unboxing will need to take place so you can add a native type variable to a `List<Object>` or assign a native variable to an element of the List.
Problem
I am manually converting code from Java (1.6) to C# and finding some difficulty with the behaviour of primitives (int and double). In C# it appears that almost all conversions happen automatically ``` List<double> list1 = new List<double>(); // legal, C# double d0 = 3.0; list1.Add(d0); // legal, C# Double dd = 2.3f; // legal, C# list1.Add(dd); // legal, C# List<Double> list2 = new List<Double>(); // legal, C# double d1 = 3.0; list2.Add(d1); // legal, C# list2.Add(2.0); // legal, C# double d2 = list2.get(0); // legal, C# ``` but in Java only some are allowed ``` List<double> list1 = new ArrayList<double>(); // illegal, Java List<Double> list2 = new ArrayList<Double>(); // legal, Java double d1 = 3.0; list2.add(d1); // legal, Java list2.add(2.0); // legal, Java double d2 = list2.get(0); // legal, Java ``` I'd be grateful for a systematic analysis of the differences and any underlying rationale.